diff mbox series

ldconfig/x86: Store ISA level in cache and aux cache

Message ID CAMe9rOpqXMsxjO79Ejio12yb76KJMcgjMptuoiJfRR9LyoVYLA@mail.gmail.com
State Superseded
Delegated to: Adhemerval Zanella Netto
Headers
Series ldconfig/x86: Store ISA level in cache and aux cache |

Commit Message

H.J. Lu Dec. 9, 2020, 3:27 a.m. UTC 
  On Tue, Dec 8, 2020 at 7:31 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Tue, Dec 8, 2020 at 7:16 AM Florian Weimer <fweimer@redhat.com> wrote:
> >
> > * H. J. Lu:
> >
> > >> > For each file entry for a shared object, the hwcap field has been used by
> > >> > DL_CACHE_HWCAP_EXTENSION for glibc-hwcaps.  Are you suggesting
> > >> > to add another file entry for the same shared object to store ISA level
> > >> > requirement?
> > >>
> > >> It's a 64-bit field.  We do this:
> > >>
> > >> /* This bit in the hwcap field of struct file_entry_new indicates that
> > >>    the lower 32 bits contain an index into the
> > >>    cache_extension_tag_glibc_hwcaps section.  Older glibc versions do
> > >>    not know about this HWCAP bit, so they will ignore these
> > >>    entries.  */
> > >> #define DL_CACHE_HWCAP_EXTENSION (1ULL << 62)
> > >>
> > >> /* Return true if the ENTRY->hwcap value indicates that
> > >>    DL_CACHE_HWCAP_EXTENSION is used.  */
> > >> static inline bool
> > >> dl_cache_hwcap_extension (struct file_entry_new *entry)
> > >> {
> > >>   /* If DL_CACHE_HWCAP_EXTENSION is set, but other bits as well, this
> > >>      is a different kind of extension.  */
> > >>   return (entry->hwcap >> 32) == (DL_CACHE_HWCAP_EXTENSION >> 32);
> > >> }
> > >>
> > >> So we can use a different bit pattern involving DL_CACHE_HWCAP_EXTENSION
> > >> to express something else.  In particular, only the lower 32 bits are
> > >> currently used as an index.
> > >
> > > So bits 33-47 can be used for ISA level requirement.  This should support
> > > 65536 ISA levels.
> >
> > The question is whether the ISA levels and the glibc-hwcaps name are
> > used in parallel.  If not, we can use  (1ULL << 62) | (1ULL << 32) as
> > the marker bits and a 32-bit index in the lower half.
> >
> > (I do not think this is necessarily relevant for levels, but it could be
> > used for locating objects according to other criteria.)
> >
>
> I think ISA level and glibc-hwcaps should go together.
>

Here is the patch to store ISA level in the portion of the unused
upper 32 bits of the hwcaps field in cache and the unused pad
field in aux cache.

Comments

Adhemerval Zanella Jan. 12, 2021, 4:25 p.m. UTC | #1 
On 09/12/2020 00:27, H.J. Lu via Libc-alpha wrote:
> On Tue, Dec 8, 2020 at 7:31 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>>
>> On Tue, Dec 8, 2020 at 7:16 AM Florian Weimer <fweimer@redhat.com> wrote:
>>>
>>> * H. J. Lu:
>>>
>>>>>> For each file entry for a shared object, the hwcap field has been used by
>>>>>> DL_CACHE_HWCAP_EXTENSION for glibc-hwcaps.  Are you suggesting
>>>>>> to add another file entry for the same shared object to store ISA level
>>>>>> requirement?
>>>>>
>>>>> It's a 64-bit field.  We do this:
>>>>>
>>>>> /* This bit in the hwcap field of struct file_entry_new indicates that
>>>>>    the lower 32 bits contain an index into the
>>>>>    cache_extension_tag_glibc_hwcaps section.  Older glibc versions do
>>>>>    not know about this HWCAP bit, so they will ignore these
>>>>>    entries.  */
>>>>> #define DL_CACHE_HWCAP_EXTENSION (1ULL << 62)
>>>>>
>>>>> /* Return true if the ENTRY->hwcap value indicates that
>>>>>    DL_CACHE_HWCAP_EXTENSION is used.  */
>>>>> static inline bool
>>>>> dl_cache_hwcap_extension (struct file_entry_new *entry)
>>>>> {
>>>>>   /* If DL_CACHE_HWCAP_EXTENSION is set, but other bits as well, this
>>>>>      is a different kind of extension.  */
>>>>>   return (entry->hwcap >> 32) == (DL_CACHE_HWCAP_EXTENSION >> 32);
>>>>> }
>>>>>
>>>>> So we can use a different bit pattern involving DL_CACHE_HWCAP_EXTENSION
>>>>> to express something else.  In particular, only the lower 32 bits are
>>>>> currently used as an index.
>>>>
>>>> So bits 33-47 can be used for ISA level requirement.  This should support
>>>> 65536 ISA levels.
>>>
>>> The question is whether the ISA levels and the glibc-hwcaps name are
>>> used in parallel.  If not, we can use  (1ULL << 62) | (1ULL << 32) as
>>> the marker bits and a 32-bit index in the lower half.
>>>
>>> (I do not think this is necessarily relevant for levels, but it could be
>>> used for locating objects according to other criteria.)
>>>
>>
>> I think ISA level and glibc-hwcaps should go together.
>>
> 
> Here is the patch to store ISA level in the portion of the unused
> upper 32 bits of the hwcaps field in cache and the unused pad
> field in aux cache.
> 
> 
> From f5053fabd1e8a5567b487ef4054793e043a7b817 Mon Sep 17 00:00:00 2001
> From: "H.J. Lu" <hjl.tools@gmail.com>
> Date: Sat, 5 Dec 2020 07:01:58 -0800
> Subject: [PATCH] ldconfig/x86: Store ISA level in cache and aux cache
> 
> Store ISA level in the portion of the unused upper 32 bits of the hwcaps
> field in cache and the unused pad field in aux cache.  ISA level is stored
> and checked only for shared objects in glibc-hwcaps subdirectories.  The
> shared objects in the default directories aren't checked since there are
> no fallbacks for these shared objects.

Some comments below, most minor changes and code organization.  The main
change I would like is to improve test coverage, as for the first patch.

> ---
>  elf/cache.c                                   | 34 +++++---
>  elf/dl-cache.c                                |  4 +
>  elf/ldconfig.c                                | 18 +++--
>  elf/readelflib.c                              | 81 ++++++++++++++++++-
>  elf/readlib.c                                 |  7 +-
>  elf/tst-glibc-hwcaps-2-cache.c                | 45 +++++++++++
>  .../etc/ld.so.conf                            |  2 +
>  .../postclean.req                             |  0
>  elf/tst-glibc-hwcaps-2-cache.script           |  6 ++
>  sysdeps/generic/dl-cache.h                    | 15 +++-
>  sysdeps/generic/dl-isa-level.h                | 26 ++++++
>  sysdeps/generic/ldconfig.h                    | 22 +++--
>  sysdeps/generic/read-prop.h                   | 35 ++++++++
>  sysdeps/unix/sysv/linux/arm/readelflib.c      | 22 ++---
>  sysdeps/unix/sysv/linux/ia64/readelflib.c     | 22 ++---
>  sysdeps/unix/sysv/linux/mips/readelflib.c     | 22 ++---
>  sysdeps/unix/sysv/linux/powerpc/readelflib.c  | 22 ++---
>  sysdeps/unix/sysv/linux/riscv/readelflib.c    | 22 ++---
>  sysdeps/unix/sysv/linux/s390/readelflib.c     | 22 ++---
>  sysdeps/unix/sysv/linux/sparc/readelflib.c    | 22 ++---
>  sysdeps/unix/sysv/linux/x86/read-prop.h       | 61 ++++++++++++++
>  sysdeps/unix/sysv/linux/x86/readelflib.c      | 23 +++---
>  sysdeps/unix/sysv/linux/x86_64/Makefile       | 31 +++++++
>  .../sysv/linux/x86_64/tst-glibc-hwcaps-2.c    | 61 ++++++++++++++
>  .../linux/x86_64/x86-64-isa-level-VALUE.c     |  4 +
>  sysdeps/x86/dl-isa-level.h                    | 32 ++++++++
>  26 files changed, 550 insertions(+), 111 deletions(-)
>  create mode 100644 elf/tst-glibc-hwcaps-2-cache.c
>  create mode 100644 elf/tst-glibc-hwcaps-2-cache.root/etc/ld.so.conf
>  create mode 100644 elf/tst-glibc-hwcaps-2-cache.root/postclean.req
>  create mode 100644 elf/tst-glibc-hwcaps-2-cache.script
>  create mode 100644 sysdeps/generic/dl-isa-level.h
>  create mode 100644 sysdeps/generic/read-prop.h
>  create mode 100644 sysdeps/unix/sysv/linux/x86/read-prop.h
>  create mode 100644 sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c
>  create mode 100644 sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
>  create mode 100644 sysdeps/x86/dl-isa-level.h
> 
> diff --git a/elf/cache.c b/elf/cache.c
> index b03c5319f8..91a72381ae 100644
> --- a/elf/cache.c
> +++ b/elf/cache.c
> @@ -145,6 +145,7 @@ struct cache_entry
>    struct stringtable_entry *path; /* Path to find library.  */
>    int flags;			/* Flags to indicate kind of library.  */
>    unsigned int osversion;	/* Required OS version.  */
> +  unsigned int isa_level;	/* Required ISAL level.  */

Maybe a typo here 'ISAL'?

>    uint64_t hwcap;		/* Important hardware capabilities.  */
>    int bits_hwcap;		/* Number of bits set in hwcap.  */
>  
> @@ -660,8 +661,14 @@ save_cache (const char *cache_name)
>  	  if (entry->hwcaps == NULL)
>  	    file_entries_new->libs[idx_new].hwcap = entry->hwcap;
>  	  else
> -	    file_entries_new->libs[idx_new].hwcap
> -	      = DL_CACHE_HWCAP_EXTENSION | entry->hwcaps->section_index;
> +	    {
> +	      if (entry->isa_level > (1 << DL_CACHE_HWCAP_ISA_LEVEL_COUNT))

Maybe wrap this on a macro at dl-cache.h? It already does it for
DL_CACHE_HWCAP_ISA_LEVEL_MASK.

> +		abort ();

Maybe use 'error (...)' to print a proper error message?

> +	      file_entries_new->libs[idx_new].hwcap
> +		= (DL_CACHE_HWCAP_EXTENSION
> +		   | (((uint64_t) entry->isa_level) << 32)
> +		   | entry->hwcaps->section_index);
> +	    }

Would be better to wrap this on a inline function at dl-cache.h?

 static inline unsigned int dl_cache_hwcap_isa_level (struct file_entry_new *entry)
 {
   return DL_CACHE_HWCAP_EXTENSION 
          | ((uint64_t) entry->isa_level << 32)
          | entry->hwcaps->sections_index;
 }

>  	  file_entries_new->libs[idx_new].key
>  	    = str_offset + entry->lib->offset;
>  	  file_entries_new->libs[idx_new].value
> @@ -776,7 +783,8 @@ save_cache (const char *cache_name)
>  /* Add one library to the cache.  */
>  void
>  add_to_cache (const char *path, const char *filename, const char *soname,
> -	      int flags, unsigned int osversion, uint64_t hwcap,
> +	      int flags, unsigned int osversion,
> +	      unsigned int isa_level, uint64_t hwcap,
>  	      struct glibc_hwcaps_subdirectory *hwcaps)
>  {
>    struct cache_entry *new_entry = xmalloc (sizeof (*new_entry));
> @@ -794,6 +802,7 @@ add_to_cache (const char *path, const char *filename, const char *soname,
>    new_entry->path = path_interned;
>    new_entry->flags = flags;
>    new_entry->osversion = osversion;
> +  new_entry->isa_level = isa_level;
>    new_entry->hwcap = hwcap;
>    new_entry->hwcaps = hwcaps;
>    new_entry->bits_hwcap = 0;

Ok.

> @@ -850,6 +859,7 @@ struct aux_cache_entry
>    struct aux_cache_entry_id id;
>    int flags;
>    unsigned int osversion;
> +  unsigned int isa_level;
>    int used;
>    char *soname;
>    struct aux_cache_entry *next;
> @@ -863,7 +873,7 @@ struct aux_cache_file_entry
>    int32_t flags;		/* This is 1 for an ELF library.  */
>    uint32_t soname;		/* String table indice.  */
>    uint32_t osversion;		/* Required OS version.	 */
> -  int32_t pad;
> +  uint32_t isa_level;		/* Required ISA level.	 */
>  };
>  

I think it would be good to have a _Static_assert with the
expected aux_cache_entry size.

>  /* ldconfig maintains an auxiliary cache file that allows
> @@ -914,7 +924,8 @@ init_aux_cache (void)
>  
>  int
>  search_aux_cache (struct stat64 *stat_buf, int *flags,
> -		  unsigned int *osversion, char **soname)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname)
>  {
>    struct aux_cache_entry_id id;
>    id.ino = (uint64_t) stat_buf->st_ino;
> @@ -932,6 +943,7 @@ search_aux_cache (struct stat64 *stat_buf, int *flags,
>        {
>  	*flags = entry->flags;
>  	*osversion = entry->osversion;
> +	*isa_level = entry->isa_level;
>  	if (entry->soname != NULL)
>  	  *soname = xstrdup (entry->soname);
>  	else

Ok.

> @@ -945,7 +957,8 @@ search_aux_cache (struct stat64 *stat_buf, int *flags,
>  
>  static void
>  insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
> -		     unsigned int osversion, const char *soname, int used)
> +		     unsigned int osversion, unsigned int isa_level,
> +		     const char *soname, int used)
>  {
>    size_t hash = aux_cache_entry_id_hash (id) % aux_hash_size;
>    struct aux_cache_entry *entry;
> @@ -961,6 +974,7 @@ insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
>    entry->id = *id;
>    entry->flags = flags;
>    entry->osversion = osversion;
> +  entry->isa_level = isa_level;
>    entry->used = used;
>    if (soname != NULL)
>      entry->soname = memcpy ((char *) (entry + 1), soname, len);

Ok.

> @@ -972,14 +986,15 @@ insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
>  
>  void
>  add_to_aux_cache (struct stat64 *stat_buf, int flags,
> -		  unsigned int osversion, const char *soname)
> +		  unsigned int osversion, unsigned int isa_level,
> +		  const char *soname)
>  {
>    struct aux_cache_entry_id id;
>    id.ino = (uint64_t) stat_buf->st_ino;
>    id.ctime = (uint64_t) stat_buf->st_ctime;
>    id.size = (uint64_t) stat_buf->st_size;
>    id.dev = (uint64_t) stat_buf->st_dev;
> -  insert_to_aux_cache (&id, flags, osversion, soname, 1);
> +  insert_to_aux_cache (&id, flags, osversion, isa_level, soname, 1);
>  }
>  
>  /* Load auxiliary cache to search for unchanged entries.   */
> @@ -1025,6 +1040,7 @@ load_aux_cache (const char *aux_cache_name)
>      insert_to_aux_cache (&aux_cache->libs[i].id,
>  			 aux_cache->libs[i].flags,
>  			 aux_cache->libs[i].osversion,
> +			 aux_cache->libs[i].isa_level,
>  			 aux_cache->libs[i].soname == 0
>  			 ? NULL : aux_cache_data + aux_cache->libs[i].soname,
>  			 0);
> @@ -1093,7 +1109,7 @@ save_aux_cache (const char *aux_cache_name)
>  	      str_offset += len;
>  	    }
>  	  file_entries->libs[idx].osversion = entry->osversion;
> -	  file_entries->libs[idx++].pad = 0;
> +	  file_entries->libs[idx++].isa_level = entry->isa_level;
>  	}
>  
>    /* Write out auxiliary cache file.  */

Ok.

> diff --git a/elf/dl-cache.c b/elf/dl-cache.c
> index 97093bb700..edeff7ccc1 100644
> --- a/elf/dl-cache.c
> +++ b/elf/dl-cache.c
> @@ -25,6 +25,7 @@
>  #include <stdint.h>
>  #include <_itoa.h>
>  #include <dl-hwcaps.h>
> +#include <dl-isa-level.h>
>  
>  #ifndef _DL_PLATFORMS_COUNT
>  # define _DL_PLATFORMS_COUNT 0
> @@ -284,6 +285,9 @@ search_cache (const char *string_table, uint32_t string_table_size,
>  
>  #ifdef SHARED
>  			  named_hwcap = dl_cache_hwcap_extension (libnew);
> +			  if (named_hwcap
> +			      && !dl_cache_hwcap_isa_level_compatible (libnew))
> +			    continue;
>  #endif
>  
>  			  /* The entries with named/extension hwcaps

Ok, so it skips non compatible ISA shared libraries.

> diff --git a/elf/ldconfig.c b/elf/ldconfig.c
> index 10927a8c7f..9dceac38aa 100644
> --- a/elf/ldconfig.c
> +++ b/elf/ldconfig.c
> @@ -655,6 +655,7 @@ manual_link (char *library)
>    struct stat64 stat_buf;
>    int flag;
>    unsigned int osversion;
> +  unsigned int isa_level;
>  
>    /* Prepare arguments for create_links call.  Split library name in
>       directory and filename first.  Since path is allocated, we've got
> @@ -721,7 +722,7 @@ manual_link (char *library)
>      }
>  
>    if (process_file (real_library, library, libname, &flag, &osversion,
> -		    &soname, 0, &stat_buf))
> +		    &isa_level, &soname, 0, &stat_buf))
>      {
>        error (0, 0, _("No link created since soname could not be found for %s"),
>  	     library);
> @@ -768,6 +769,7 @@ struct dlib_entry
>    int flag;
>    int is_link;
>    unsigned int osversion;
> +  unsigned int isa_level;
>    struct dlib_entry *next;
>  };
>  

Ok.

> @@ -980,17 +982,21 @@ search_dir (const struct dir_entry *entry)
>  	 library already and it's not changed.  */
>        char *soname;
>        unsigned int osversion;
> -      if (!search_aux_cache (&lstat_buf, &flag, &osversion, &soname))
> +      unsigned int isa_level;
> +      if (!search_aux_cache (&lstat_buf, &flag, &osversion, &isa_level,
> +			     &soname))
>  	{
>  	  if (process_file (real_name, file_name, direntry->d_name, &flag,
> -			    &osversion, &soname, is_link, &lstat_buf))
> +			    &osversion, &isa_level, &soname, is_link,
> +			    &lstat_buf))
>  	    {
>  	      if (real_name != real_file_name)
>  		free (real_name);
>  	      continue;
>  	    }
>  	  else if (opt_build_cache)
> -	    add_to_aux_cache (&lstat_buf, flag, osversion, soname);
> +	    add_to_aux_cache (&lstat_buf, flag, osversion, isa_level,
> +			      soname);
>  	}
>  
>        if (soname == NULL)

Ok.

> @@ -1096,6 +1102,7 @@ search_dir (const struct dir_entry *entry)
>  		  dlib_ptr->name = xstrdup (direntry->d_name);
>  		  dlib_ptr->is_link = is_link;
>  		  dlib_ptr->osversion = osversion;
> +		  dlib_ptr->isa_level = isa_level;
>  		}
>  	      /* Don't add this library, abort loop.  */
>  	      /* Also free soname, since it's dynamically allocated.  */
> @@ -1112,6 +1119,7 @@ search_dir (const struct dir_entry *entry)
>  	  dlib_ptr->flag = flag;
>  	  dlib_ptr->is_link = is_link;
>  	  dlib_ptr->osversion = osversion;
> +	  dlib_ptr->isa_level = isa_level;
>  	  /* Add at head of list.  */
>  	  dlib_ptr->next = dlibs;
>  	  dlibs = dlib_ptr;
> @@ -1149,7 +1157,7 @@ search_dir (const struct dir_entry *entry)
>        if (opt_build_cache)
>  	add_to_cache (entry->path, filename, dlib_ptr->soname,
>  		      dlib_ptr->flag, dlib_ptr->osversion,
> -		      hwcap, entry->hwcaps);
> +		      dlib_ptr->isa_level, hwcap, entry->hwcaps);
>      }
>  
>    /* Free all resources.  */

Ok.

> diff --git a/elf/readelflib.c b/elf/readelflib.c
> index 5905f6d344..abb1ac61fa 100644
> --- a/elf/readelflib.c
> +++ b/elf/readelflib.c
> @@ -17,6 +17,8 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> +#include <read-prop.h>
> +
>  /* This code is a heavily simplified version of the readelf program
>     that's part of the current binutils development version.  For architectures
>     which need to handle both 32bit and 64bit ELF libraries,  this file is
> @@ -40,8 +42,8 @@ do								\
>  /* Returns 0 if everything is ok, != 0 in case of error.  */
>  int
>  process_elf_file (const char *file_name, const char *lib, int *flag,
> -		  unsigned int *osversion, char **soname, void *file_contents,
> -		  size_t file_length)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname, void *file_contents, size_t file_length)
>  {
>    int i;
>    unsigned int j;
> @@ -86,6 +88,9 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
>       libc5/libc6.  */
>    *flag = FLAG_ELF;
>  
> +  /* The default ISA level is 0.  */
> +  *isa_level = 0;
> +
>    dynamic_addr = 0;
>    dynamic_size = 0;
>    program_interpreter = NULL;
> @@ -164,6 +169,78 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
>  	    }
>  	  break;
>  
> +	case PT_GNU_PROPERTY:
> +	  /* The NT_GNU_PROPERTY_TYPE_0 note must be aligned to 4 bytes
> +	     in 32-bit objects and to 8 bytes in 64-bit objects.  Skip
> +	     notes with incorrect alignment.  */
> +	  if (segment->p_align == (__ELF_NATIVE_CLASS / 8))
> +	    {
> +	      const ElfW(Nhdr) *note = (const void *) (file_contents
> +						       + segment->p_offset);
> +	      const ElfW(Addr) size = segment->p_filesz;
> +	      const ElfW(Addr) align = segment->p_align;
> +
> +	      const ElfW(Addr) start = (ElfW(Addr)) (uintptr_t) note;
> +	      unsigned int last_type = 0;
> +
> +	      while ((ElfW(Addr)) (uintptr_t) (note + 1) - start < size)
> +		{
> +		  /* Find the NT_GNU_PROPERTY_TYPE_0 note.  */
> +		  if (note->n_namesz == 4
> +		      && note->n_type == NT_GNU_PROPERTY_TYPE_0
> +		      && memcmp (note + 1, "GNU", 4) == 0)
> +		    {
> +		      /* Check for invalid property.  */
> +		      if (note->n_descsz < 8
> +			  || (note->n_descsz % sizeof (ElfW(Addr))) != 0)
> +			goto done;
> +
> +		      /* Start and end of property array.  */
> +		      unsigned char *ptr = (unsigned char *) (note + 1) + 4;
> +		      unsigned char *ptr_end = ptr + note->n_descsz;
> +
> +		      do
> +			{
> +			  unsigned int type = *(unsigned int *) ptr;
> +			  unsigned int datasz = *(unsigned int *) (ptr + 4);
> +
> +			  /* Property type must be in ascending order.  */
> +			  if (type < last_type)
> +			    goto done;
> +
> +			  ptr += 8;
> +			  if ((ptr + datasz) > ptr_end)
> +			    goto done;
> +
> +			  last_type = type;
> +
> +			  /* Target specific property processing.
> +			     Return value:
> +			       false: Continue processing the properties.
> +			       true : Stop processing the properties.
> +			   */
> +			  if (read_gnu_property (isa_level, type,
> +						 datasz, ptr))
> +			    goto done;
> +
> +			  /* Check the next property item.  */
> +			  ptr += ALIGN_UP (datasz, sizeof (ElfW(Addr)));
> +			}
> +		      while ((ptr_end - ptr) >= 8);
> +
> +		      /* Only handle one NT_GNU_PROPERTY_TYPE_0.  */
> +		      goto done;
> +		    }
> +
> +		  note = ((const void *) note
> +			  + ELF_NOTE_NEXT_OFFSET (note->n_namesz,
> +						  note->n_descsz,
> +						  align));
> +		}
> +	    }
> +done:
> +	  break;
> +
>  	default:
>  	  break;
>  	}

Ok, although this is quite similar to the _dl_process_pt_gnu_property
(maybe a future work to try refactor both to use a common code).

> diff --git a/elf/readlib.c b/elf/readlib.c
> index 994a4426a1..def0eafbeb 100644
> --- a/elf/readlib.c
> +++ b/elf/readlib.c
> @@ -75,7 +75,8 @@ is_gdb_python_file (const char *name)
>  int
>  process_file (const char *real_file_name, const char *file_name,
>  	      const char *lib, int *flag, unsigned int *osversion,
> -	      char **soname, int is_link, struct stat64 *stat_buf)
> +	      unsigned int *isa_level, char **soname, int is_link,
> +	      struct stat64 *stat_buf)
>  {
>    FILE *file;
>    struct stat64 statbuf;
> @@ -173,8 +174,8 @@ process_file (const char *real_file_name, const char *file_name,
>    /* Libraries have to be shared object files.  */
>    else if (elf_header->e_type != ET_DYN)
>      ret = 1;
> -  else if (process_elf_file (file_name, lib, flag, osversion, soname,
> -			     file_contents, statbuf.st_size))
> +  else if (process_elf_file (file_name, lib, flag, osversion, isa_level,
> +			     soname, file_contents, statbuf.st_size))
>      ret = 1;
>  
>   done:

Ok.

> diff --git a/elf/tst-glibc-hwcaps-2-cache.c b/elf/tst-glibc-hwcaps-2-cache.c
> new file mode 100644
> index 0000000000..2c30a2c911
> --- /dev/null
> +++ b/elf/tst-glibc-hwcaps-2-cache.c
> @@ -0,0 +1,45 @@
> +/* Wrapper to invoke tst-glibc-hwcaps-2 in a container to test ldconfig.
> +   Copyright (C) 2020 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* This program is just a wrapper that runs ldconfig followed by
> +   tst-glibc-hwcaps-2.  The actual test is provided via an
> +   implementation in a sysdeps subdirectory.  */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <support/support.h>
> +#include <unistd.h>
> +
> +int
> +main (int argc, char **argv)
> +{
> +  /* Run ldconfig to populate the cache.  */
> +  {
> +    char *command = xasprintf ("%s/ldconfig", support_install_rootsbindir);
> +    if (system (command) != 0)
> +      return 1;
> +    free (command);
> +  }

Maybe use support_capture_subprogram here?

  char *command = xasprintf ("%s/ldconfig", support_install_rootsbindir); 
  struct support_capture_subprocess result = 
    support_capture_subprogram (command,  &((char *) { NULL }));
  support_capture_subprocess_check (&result, "ldconfig", 0, sc_allow_none);
  free (command);  

> +
> +  /* Reuse tst-glibc-hwcaps.  Since this code is running in a
> +     container, we can launch it directly.  */
> +  char *path = xasprintf ("%s/elf/tst-glibc-hwcaps-2", support_objdir_root);
> +  execv (path, argv);
> +  printf ("error: execv of %s failed: %m\n", path);
> +  return 1;
> +}

Ok.

> diff --git a/elf/tst-glibc-hwcaps-2-cache.root/etc/ld.so.conf b/elf/tst-glibc-hwcaps-2-cache.root/etc/ld.so.conf
> new file mode 100644
> index 0000000000..e1e74dbda2
> --- /dev/null
> +++ b/elf/tst-glibc-hwcaps-2-cache.root/etc/ld.so.conf
> @@ -0,0 +1,2 @@
> +# This file was created to suppress a warning from ldconfig:
> +# /sbin/ldconfig: Warning: ignoring configuration file that cannot be opened: /etc/ld.so.conf: No such file or directory
> diff --git a/elf/tst-glibc-hwcaps-2-cache.root/postclean.req b/elf/tst-glibc-hwcaps-2-cache.root/postclean.req
> new file mode 100644
> index 0000000000..e69de29bb2

Ok.

> diff --git a/elf/tst-glibc-hwcaps-2-cache.script b/elf/tst-glibc-hwcaps-2-cache.script
> new file mode 100644
> index 0000000000..29ccfc3b49
> --- /dev/null
> +++ b/elf/tst-glibc-hwcaps-2-cache.script
> @@ -0,0 +1,6 @@
> +# test-container does not support scripts in sysdeps directories, so
> +# collect everything in one file.
> +
> +mkdirp 0770 $L/glibc-hwcaps/x86-64-v2

Ok.

> +cp $B/elf/libx86-64-isa-level-1.so $L/libx86-64-isa-level.so
> +cp $B/elf/libx86-64-isa-level-4.so $L/glibc-hwcaps/x86-64-v2/libx86-64-isa-level.so
> diff --git a/sysdeps/generic/dl-cache.h b/sysdeps/generic/dl-cache.h
> index 72a66b45ee..1138228e5c 100644
> --- a/sysdeps/generic/dl-cache.h
> +++ b/sysdeps/generic/dl-cache.h
> @@ -106,14 +106,23 @@ struct file_entry_new
>     entries.  */
>  #define DL_CACHE_HWCAP_EXTENSION (1ULL << 62)
>  
> +/* The number of the ISA level bits in the upper 32 bits of the hwcap
> +   field.  */
> +#define DL_CACHE_HWCAP_ISA_LEVEL_COUNT 10
> +
> +/* The mask of the ISA level bits in the hwcap field.  */
> +#define DL_CACHE_HWCAP_ISA_LEVEL_MASK \
> +  ((1 << DL_CACHE_HWCAP_ISA_LEVEL_COUNT) -1)
> +

Space after '-'.

>  /* Return true if the ENTRY->hwcap value indicates that
>     DL_CACHE_HWCAP_EXTENSION is used.  */
>  static inline bool
>  dl_cache_hwcap_extension (struct file_entry_new *entry)
>  {
> -  /* If DL_CACHE_HWCAP_EXTENSION is set, but other bits as well, this
> -     is a different kind of extension.  */
> -  return (entry->hwcap >> 32) == (DL_CACHE_HWCAP_EXTENSION >> 32);
> +  /* If DL_CACHE_HWCAP_EXTENSION is set, but other bits, except for the
> +     ISA level bits, as well, this is a different kind of extension.  */
> +  return (((entry->hwcap >> 32) & ~DL_CACHE_HWCAP_ISA_LEVEL_MASK)
> +	  == (DL_CACHE_HWCAP_EXTENSION >> 32));
>  }
>  
>  /* See flags member of struct cache_file_new below.  */

The comment sounds confusing.

> diff --git a/sysdeps/generic/dl-isa-level.h b/sysdeps/generic/dl-isa-level.h
> new file mode 100644
> index 0000000000..77735775b9
> --- /dev/null
> +++ b/sysdeps/generic/dl-isa-level.h
> @@ -0,0 +1,26 @@
> +/* Support for reading ISA level in /etc/ld.so.cache files written by
> +   Linux ldconfig.  Generic version.
> +   Copyright (C) 2020 Free Software Foundation, Inc.

s/2020/2021

> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* Return true if the ISA level in ENTRY is compatible with CPU.  */
> +

My understanding is for function comment there is no need to add an
extra newline.

> +static inline bool
> +dl_cache_hwcap_isa_level_compatible (struct file_entry_new *entry)
> +{
> +  return true;
> +}

Ok.

> diff --git a/sysdeps/generic/ldconfig.h b/sysdeps/generic/ldconfig.h
> index 1ad1528890..a5ed350237 100644
> --- a/sysdeps/generic/ldconfig.h
> +++ b/sysdeps/generic/ldconfig.h
> @@ -70,8 +70,9 @@ const char *glibc_hwcaps_subdirectory_name
>    (const struct glibc_hwcaps_subdirectory *);
>  
>  extern void add_to_cache (const char *path, const char *filename,
> -			  const char *soname,
> -			  int flags, unsigned int osversion, uint64_t hwcap,
> +			  const char *soname, int flags,
> +			  unsigned int osversion, unsigned int isa_level,
> +			  uint64_t hwcap,
>  			  struct glibc_hwcaps_subdirectory *);
>  
>  extern void init_aux_cache (void);
> @@ -79,23 +80,28 @@ extern void init_aux_cache (void);
>  extern void load_aux_cache (const char *aux_cache_name);
>  
>  extern int search_aux_cache (struct stat64 *stat_buf, int *flags,
> -			     unsigned int *osversion, char **soname);
> +			     unsigned int *osversion,
> +			     unsigned int *isa_level, char **soname);
>  
>  extern void add_to_aux_cache (struct stat64 *stat_buf, int flags,
> -			      unsigned int osversion, const char *soname);
> +			      unsigned int osversion,
> +			      unsigned int isa_level, const char *soname);
>  
>  extern void save_aux_cache (const char *aux_cache_name);
>  
>  /* Declared in readlib.c.  */
>  extern int process_file (const char *real_file_name, const char *file_name,
> -			 const char *lib, int *flag, unsigned int *osversion,
> -			 char **soname, int is_link, struct stat64 *stat_buf);
> +			 const char *lib, int *flag,
> +			 unsigned int *osversion, unsigned int *isa_level,
> +			 char **soname, int is_link,
> +			 struct stat64 *stat_buf);
>  
>  extern char *implicit_soname (const char *lib, int flag);
>  
>  /* Declared in readelflib.c.  */
> -extern int process_elf_file (const char *file_name, const char *lib, int *flag,
> -			     unsigned int *osversion, char **soname,
> +extern int process_elf_file (const char *file_name, const char *lib,
> +			     int *flag, unsigned int *osversion,
> +			     unsigned int *isa_level, char **soname,
>  			     void *file_contents, size_t file_length);
>  
>  /* Declared in chroot_canon.c.  */


Ok.

> diff --git a/sysdeps/generic/read-prop.h b/sysdeps/generic/read-prop.h
> new file mode 100644
> index 0000000000..091bd2f6c1
> --- /dev/null
> +++ b/sysdeps/generic/read-prop.h

Maybe elf-read-prop.h to add more information on exactly this
file intends to?

> @@ -0,0 +1,35 @@
> +/* Support for GNU properties in ldconfig.  Generic version.
> +   Copyright (C) 2020 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _READ_PROP_H
> +#define _READ_PROP_H
> +
> +/* Called for each property in the NT_GNU_PROPERTY_TYPE_0 note of SEGMENT.
> +   Return value:
> +     false: Continue processing the properties.
> +     true : Stop processing the properties.
> + */
> +
> +static inline bool __attribute__ ((always_inline))
> +read_gnu_property (unsigned int *isal_level, uint32_t type, uint32_t
> +		   datasz, void *data)
> +{
> +  return true;
> +}
> +
> +#endif

Ok.

> diff --git a/sysdeps/unix/sysv/linux/arm/readelflib.c b/sysdeps/unix/sysv/linux/arm/readelflib.c
> index 9d03fa6405..7f444add14 100644
> --- a/sysdeps/unix/sysv/linux/arm/readelflib.c
> +++ b/sysdeps/unix/sysv/linux/arm/readelflib.c
> @@ -18,18 +18,20 @@
>     <https://www.gnu.org/licenses/>.  */
>  
>  
> -int process_elf32_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf32_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
> -int process_elf64_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf64_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
>  
>  /* Returns 0 if everything is ok, != 0 in case of error.  */
>  int
>  process_elf_file (const char *file_name, const char *lib, int *flag,
> -		  unsigned int *osversion, char **soname, void *file_contents,
> -		  size_t file_length)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname, void *file_contents, size_t file_length)
>  {
>    ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
>    int ret;
> @@ -38,8 +40,8 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
>      {
>        Elf32_Ehdr *elf32_header = (Elf32_Ehdr *) elf_header;
>  
> -      ret = process_elf32_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>  
>        if (!ret && EF_ARM_EABI_VERSION (elf32_header->e_flags) == EF_ARM_EABI_VER5)
>  	{
> @@ -57,8 +59,8 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
>      }
>    else
>      {
> -      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>        /* AArch64 libraries are always libc.so.6+.  */
>        if (!ret)
>  	*flag = FLAG_AARCH64_LIB64|FLAG_ELF_LIBC6;

Ok.

> diff --git a/sysdeps/unix/sysv/linux/ia64/readelflib.c b/sysdeps/unix/sysv/linux/ia64/readelflib.c
> index d24a934351..19d37b438e 100644
> --- a/sysdeps/unix/sysv/linux/ia64/readelflib.c
> +++ b/sysdeps/unix/sysv/linux/ia64/readelflib.c
> @@ -16,29 +16,31 @@
>     <https://www.gnu.org/licenses/>.  */
>  
>  
> -int process_elf32_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf32_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
> -int process_elf64_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf64_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
>  
>  /* Returns 0 if everything is ok, != 0 in case of error.  */
>  int
>  process_elf_file (const char *file_name, const char *lib, int *flag,
> -		  unsigned int *osversion, char **soname,
> -		  void *file_contents, size_t file_length)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname, void *file_contents, size_t file_length)
>  {
>    ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
>    int ret;
>  
>    if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
> -    return process_elf32_file (file_name, lib, flag, osversion, soname,
> -			       file_contents, file_length);
> +    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
> +			       soname, file_contents, file_length);
>    else
>      {
> -      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>        /* Intel 64bit libraries are always libc.so.6+.  */
>        if (!ret)
>  	*flag = FLAG_IA64_LIB64|FLAG_ELF_LIBC6;

Ok.

> diff --git a/sysdeps/unix/sysv/linux/mips/readelflib.c b/sysdeps/unix/sysv/linux/mips/readelflib.c
> index 8363b8afcc..a3399961c9 100644
> --- a/sysdeps/unix/sysv/linux/mips/readelflib.c
> +++ b/sysdeps/unix/sysv/linux/mips/readelflib.c
> @@ -20,18 +20,20 @@
>     <https://www.gnu.org/licenses/>.  */
>  
>  
> -int process_elf32_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf32_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
> -int process_elf64_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf64_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
>  
>  /* Returns 0 if everything is ok, != 0 in case of error.  */
>  int
>  process_elf_file (const char *file_name, const char *lib, int *flag,
> -		  unsigned int *osversion, char **soname, void *file_contents,
> -		  size_t file_length)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname, void *file_contents, size_t file_length)
>  {
>    union
>      {
> @@ -45,8 +47,8 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
>    elf_header.eh = file_contents;
>    if (elf_header.eh->e_ident [EI_CLASS] == ELFCLASS32)
>      {
> -      ret = process_elf32_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>        if (!ret)
>  	{
>  	  Elf32_Word flags = elf_header.eh32->e_flags;
> @@ -62,8 +64,8 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
>      }
>    else
>      {
> -      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>        /* n64 libraries are always libc.so.6+.  */
>        if (!ret)
>  	{

Ok.

> diff --git a/sysdeps/unix/sysv/linux/powerpc/readelflib.c b/sysdeps/unix/sysv/linux/powerpc/readelflib.c
> index eb20680418..ce01658fb3 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/readelflib.c
> +++ b/sysdeps/unix/sysv/linux/powerpc/readelflib.c
> @@ -17,29 +17,31 @@
>     <https://www.gnu.org/licenses/>.  */
>  
>  
> -int process_elf32_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf32_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
> -int process_elf64_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf64_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
>  
>  /* Returns 0 if everything is ok, != 0 in case of error.  */
>  int
>  process_elf_file (const char *file_name, const char *lib, int *flag,
> -		  unsigned int *osversion, char **soname, void *file_contents,
> -		  size_t file_length)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname, void *file_contents, size_t file_length)
>  {
>    ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
>    int ret;
>  
>    if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
> -    return process_elf32_file (file_name, lib, flag, osversion, soname,
> -			       file_contents, file_length);
> +    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
> +			       soname, file_contents, file_length);
>    else
>      {
> -      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>        /* PowerPC 64bit libraries are always libc.so.6+.  */
>        if (!ret)
>  	*flag = FLAG_POWERPC_LIB64|FLAG_ELF_LIBC6;

Ok.

> diff --git a/sysdeps/unix/sysv/linux/riscv/readelflib.c b/sysdeps/unix/sysv/linux/riscv/readelflib.c
> index 1e70735cc0..98ae3c0b2b 100644
> --- a/sysdeps/unix/sysv/linux/riscv/readelflib.c
> +++ b/sysdeps/unix/sysv/linux/riscv/readelflib.c
> @@ -17,11 +17,13 @@
>     <https://www.gnu.org/licenses/>.  */
>  
>  
> -int process_elf32_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf32_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
> -int process_elf64_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf64_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
>  
>  /* The ELF flags supported by our current glibc port:
> @@ -38,8 +40,8 @@ int process_elf64_file (const char *file_name, const char *lib, int *flag,
>  /* Returns 0 if everything is ok, != 0 in case of error.  */
>  int
>  process_elf_file (const char *file_name, const char *lib, int *flag,
> -		  unsigned int *osversion, char **soname, void *file_contents,
> -		  size_t file_length)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname, void *file_contents, size_t file_length)
>  {
>    ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
>    Elf32_Ehdr *elf32_header = (Elf32_Ehdr *) elf_header;
> @@ -52,14 +54,14 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
>  
>    if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
>      {
> -      ret = process_elf32_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>        flags = elf32_header->e_flags;
>      }
>    else
>      {
> -      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>        flags = elf64_header->e_flags;
>      }
>  

Ok.

> diff --git a/sysdeps/unix/sysv/linux/s390/readelflib.c b/sysdeps/unix/sysv/linux/s390/readelflib.c
> index 1718efc9f9..6d19e351ba 100644
> --- a/sysdeps/unix/sysv/linux/s390/readelflib.c
> +++ b/sysdeps/unix/sysv/linux/s390/readelflib.c
> @@ -16,29 +16,31 @@
>     <https://www.gnu.org/licenses/>.  */
>  
>  
> -int process_elf32_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf32_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
> -int process_elf64_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf64_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
>  
>  /* Returns 0 if everything is ok, != 0 in case of error.  */
>  int
>  process_elf_file (const char *file_name, const char *lib, int *flag,
> -		  unsigned int *osversion, char **soname, void *file_contents,
> -		  size_t file_length)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname, void *file_contents, size_t file_length)
>  {
>    ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
>    int ret;
>  
>    if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
> -    return process_elf32_file (file_name, lib, flag, osversion, soname,
> -			       file_contents, file_length);
> +    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
> +			       soname, file_contents, file_length);
>    else
>      {
> -      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>        /* S/390 64bit libraries are always libc.so.6+.  */
>        if (!ret)
>  	*flag = FLAG_S390_LIB64|FLAG_ELF_LIBC6;

Ok.

> diff --git a/sysdeps/unix/sysv/linux/sparc/readelflib.c b/sysdeps/unix/sysv/linux/sparc/readelflib.c
> index e027a11a37..3768003925 100644
> --- a/sysdeps/unix/sysv/linux/sparc/readelflib.c
> +++ b/sysdeps/unix/sysv/linux/sparc/readelflib.c
> @@ -18,29 +18,31 @@
>     <https://www.gnu.org/licenses/>.  */
>  
>  
> -int process_elf32_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf32_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
> -int process_elf64_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf64_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
>  
>  /* Returns 0 if everything is ok, != 0 in case of error.  */
>  int
>  process_elf_file (const char *file_name, const char *lib, int *flag,
> -		  unsigned int *osversion, char **soname, void *file_contents,
> -		  size_t file_length)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname, void *file_contents, size_t file_length)
>  {
>    ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
>    int ret;
>  
>    if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
> -    return process_elf32_file (file_name, lib, flag, osversion, soname,
> -			       file_contents, file_length);
> +    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
> +			       soname, file_contents, file_length);
>    else
>      {
> -      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
> -				file_contents, file_length);
> +      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
> +				soname, file_contents, file_length);
>        /* Sparc 64bit libraries are always libc.so.6+.  */
>        if (!ret)
>  	*flag = FLAG_SPARC_LIB64|FLAG_ELF_LIBC6;

Ok.

> diff --git a/sysdeps/unix/sysv/linux/x86/read-prop.h b/sysdeps/unix/sysv/linux/x86/read-prop.h
> new file mode 100644
> index 0000000000..ac37fbc449
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86/read-prop.h
> @@ -0,0 +1,61 @@
> +/* Support for GNU properties in ldconfig.  x86 version.
> +   Copyright (C) 2020 Free Software Foundation, Inc.

s/2020/2021.

> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _READ_PROP_H
> +#define _READ_PROP_H
> +
> +#include <dl-cache.h>
> +
> +/* Called for each property in the NT_GNU_PROPERTY_TYPE_0 note of SEGMENT.
> +   Return value:
> +     false: Continue processing the properties.
> +     true : Stop processing the properties.
> + */
> +
> +static inline bool __attribute__ ((always_inline))
> +read_gnu_property (unsigned int *isal_level, uint32_t type,
> +		   uint32_t datasz, void *data)
> +{
> +  /* Property type must be in ascending order.  */
> +  if (type > GNU_PROPERTY_X86_ISA_1_NEEDED)
> +    return true;
> +
> +  if (type == GNU_PROPERTY_X86_ISA_1_NEEDED)
> +    {
> +      if (datasz == 4)
> +	{
> +	  /* The size of GNU_PROPERTY_X86_ISA_1_NEEDED must be 4 bytes.
> +	     There is no point to continue if this type is ill-formed.  */
> +	  unsigned int isa_1_needed = *(unsigned int *) data;
> +	  _Static_assert (((sizeof (isa_1_needed) * 8)
> +			   <= (1 << DL_CACHE_HWCAP_ISA_LEVEL_COUNT)),
> +			  "DL_CACHE_HWCAP_ISA_LEVEL_COUNT is too small");
> +	  if (isa_1_needed)

Implicit check.

> +	    {
> +	      unsigned int level;
> +	      asm ("bsr %1, %0" : "=r" (level) : "g" (isa_1_needed));
> +	      *isal_level = level;
> +	    }
> +	}
> +      return true;
> +    }
> +
> +  return false;
> +}
> +
> +#endif

Ok.

> diff --git a/sysdeps/unix/sysv/linux/x86/readelflib.c b/sysdeps/unix/sysv/linux/x86/readelflib.c
> index 3e83419f5b..716629bf10 100644
> --- a/sysdeps/unix/sysv/linux/x86/readelflib.c
> +++ b/sysdeps/unix/sysv/linux/x86/readelflib.c
> @@ -17,19 +17,20 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -
> -int process_elf32_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf32_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
> -int process_elf64_file (const char *file_name, const char *lib, int *flag,
> -			unsigned int *osversion, char **soname,
> +int process_elf64_file (const char *file_name, const char *lib,
> +			int *flag, unsigned int *osversion,
> +			unsigned int *isa_level, char **soname,
>  			void *file_contents, size_t file_length);
>  
>  /* Returns 0 if everything is ok, != 0 in case of error.  */
>  int
>  process_elf_file (const char *file_name, const char *lib, int *flag,
> -		  unsigned int *osversion, char **soname, void *file_contents,
> -		  size_t file_length)
> +		  unsigned int *osversion, unsigned int *isa_level,
> +		  char **soname, void *file_contents, size_t file_length)
>  {
>    ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
>    int ret, file_flag = 0;
> @@ -68,11 +69,11 @@ failed:
>      }
>  
>    if (elf_header->e_ident[EI_CLASS] == ELFCLASS32)
> -    ret = process_elf32_file (file_name, lib, flag, osversion, soname,
> -			      file_contents, file_length);
> +    ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
> +			      soname, file_contents, file_length);
>    else
> -    ret = process_elf64_file (file_name, lib, flag, osversion, soname,
> -			      file_contents, file_length);
> +    ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
> +			      soname, file_contents, file_length);
>  
>    if (!ret && file_flag)
>      *flag = file_flag;

Ok.

> diff --git a/sysdeps/unix/sysv/linux/x86_64/Makefile b/sysdeps/unix/sysv/linux/x86_64/Makefile
> index 9b82155393..9a7b3cd8e5 100644
> --- a/sysdeps/unix/sysv/linux/x86_64/Makefile
> +++ b/sysdeps/unix/sysv/linux/x86_64/Makefile
> @@ -13,3 +13,34 @@ endif
>  ifeq ($(subdir),misc)
>  gen-as-const-headers += sigaltstack-offsets.sym
>  endif
> +
> +ifeq ($(subdir),elf)
> +ifeq (yesyes,$(enable-x86-isa-level)$(config-cflags-skylake-avx512))

As for first patch, I think we should extend the test coverage to check not
only for config-cflags-skylake-avx512.  It means to build at least one
shared object with different ISA levels and run the ldconfig and check the
output against the system supported ISA level.

> +tests += tst-glibc-hwcaps-2
> +ifeq (no,$(build-hardcoded-path-in-tests))
> +# This is an ld.so.cache test, and RPATH/RUNPATH in the executable
> +# interferes with its test objectives.
> +tests-container += tst-glibc-hwcaps-2-cache
> +endif
> +modules-names += libx86-64-isa-level-1 libx86-64-isa-level-4
> +
> +$(objpfx)tst-glibc-hwcaps-2: $(objpfx)libx86-64-isa-level.so
> +
> +$(objpfx)tst-glibc-hwcaps-2.out: \
> +  $(objpfx)glibc-hwcaps/x86-64-v4/libx86-64-isa-level.so
> +$(objpfx)glibc-hwcaps/x86-64-v4/libx86-64-isa-level.so: \
> +  $(objpfx)libx86-64-isa-level-4.so
> +	cp $< $@
> +
> +CFLAGS-libx86-64-isa-level-1.os += -march=x86-64
> +CFLAGS-libx86-64-isa-level-4.os += -march=skylake-avx512
> +
> +# The test modules are parameterized by preprocessor macros.
> +LDFLAGS-libx86-64-isa-level-1.so += -Wl,-soname,libx86-64-isa-level.so
> +LDFLAGS-libx86-64-isa-level-4.so += -Wl,-soname,libx86-64-isa-level.so
> +$(objpfx)libx86-64-isa-level%.os: $(..)/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
> +	$(compile-command.c) -DVALUE=$(lastword $(subst -, ,$*))
> +$(objpfx)libx86-64-isa-level.so: $(objpfx)libx86-64-isa-level-1.so
> +	cp $< $@
> +endif
> +endif # $(subdir) == elf
> diff --git a/sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c b/sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c
> new file mode 100644
> index 0000000000..8d6b17d658
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c
> @@ -0,0 +1,61 @@
> +/* Check ISA level on shared object in glibc-hwcaps subdirectories.
> +   Copyright (C) 2020 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <stdlib.h>
> +#include <stdio.h>
> +#include <elf.h>
> +#include <get-isa-level.h>
> +#include <support/check.h>
> +#include <support/test-driver.h>
> +
> +extern int dso_isa_level (void);
> +
> +static int
> +do_test (void)
> +{
> +  const struct cpu_features *cpu_features
> +    = __x86_get_cpu_features (COMMON_CPUID_INDEX_MAX);
> +  unsigned int isa_level = get_isa_level (cpu_features);
> +  int level = dso_isa_level ();
> +  int ret;
> +  switch (level)
> +    {
> +    case 1:
> +      /* The default libx86-64-isa-level.so should be used.  */
> +      printf ("The default shared library is used.\n");
> +      if ((isa_level & GNU_PROPERTY_X86_ISA_1_V4) != 0)
> +	ret = EXIT_FAILURE;
> +      else
> +	ret = EXIT_SUCCESS;
> +      break;
> +    case 4:
> +      /* libx86-64-isa-level.so marked as x86-64 ISA level 4 needed in
> +	 x86-64-v2 should be ignored on lesser CPU.  */
> +      printf ("x86-64 ISA level 4 shared library in x86-64-v2 is used.\n");
> +      if ((isa_level & GNU_PROPERTY_X86_ISA_1_V4) != 0)
> +	ret = EXIT_SUCCESS;
> +      else
> +	ret = EXIT_FAILURE;
> +      break;
> +    default:
> +      abort ();
> +    }
> +  return ret;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c b/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
> new file mode 100644
> index 0000000000..2813d627cc
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
> @@ -0,0 +1,4 @@
> +#define INCLUDE_X86_ISA_LEVEL
> +#define MARKER dso_isa_level
> +#include <isa-level.c>
> +#include <markermodMARKER-VALUE.c>
> diff --git a/sysdeps/x86/dl-isa-level.h b/sysdeps/x86/dl-isa-level.h
> new file mode 100644
> index 0000000000..c6ed8fb9d2
> --- /dev/null
> +++ b/sysdeps/x86/dl-isa-level.h
> @@ -0,0 +1,32 @@
> +/* Support for reading ISA level in /etc/ld.so.cache files written by
> +   Linux ldconfig.  x86 version.
> +   Copyright (C) 2020 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <sys/platform/x86.h>
> +
> +/* Return true if the ISA level in ENTRY is compatible with CPU.  */
> +
> +static inline bool
> +dl_cache_hwcap_isa_level_compatible (struct file_entry_new *entry)
> +{
> +  const struct cpu_features *cpu_features = __get_cpu_features ();
> +  unsigned int isa_level
> +    = 1 << ((entry->hwcap >> 32) & DL_CACHE_HWCAP_ISA_LEVEL_MASK);
> +
> +  return (isa_level & cpu_features->isa_1) == isa_level;
> +}

Ok.

> -- 
> 2.29.2
Florian Weimer Jan. 28, 2021, 8:20 p.m. UTC | #2 
* H. J. Lu via Libc-alpha:

> Subject: [PATCH] ldconfig/x86: Store ISA level in cache and aux cache
>
> Store ISA level in the portion of the unused upper 32 bits of the hwcaps
> field in cache and the unused pad field in aux cache.  ISA level is stored
> and checked only for shared objects in glibc-hwcaps subdirectories.  The
> shared objects in the default directories aren't checked since there are
> no fallbacks for these shared objects.

Why is it necessary to duplicate the ISA levels in the cache when they
are implied by the subdirectory name?

I would have expected to store the ISA levels in the cache for DSOs
*not* in glibc-hwcaps subdirectories.  The redundancy does not make
sense to me.

ldconfig checking for matches between ISA levels and subdirectory names
makes sense too.

Thanks,
Florian
H.J. Lu Jan. 28, 2021, 8:43 p.m. UTC | #3 
On Thu, Jan 28, 2021 at 12:20 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu via Libc-alpha:
>
> > Subject: [PATCH] ldconfig/x86: Store ISA level in cache and aux cache
> >
> > Store ISA level in the portion of the unused upper 32 bits of the hwcaps
> > field in cache and the unused pad field in aux cache.  ISA level is stored
> > and checked only for shared objects in glibc-hwcaps subdirectories.  The
> > shared objects in the default directories aren't checked since there are
> > no fallbacks for these shared objects.
>
> Why is it necessary to duplicate the ISA levels in the cache when they
> are implied by the subdirectory name?
>
> I would have expected to store the ISA levels in the cache for DSOs
> *not* in glibc-hwcaps subdirectories.  The redundancy does not make
> sense to me.
>
> ldconfig checking for matches between ISA levels and subdirectory names
> makes sense too.
>

A v4 DSO may be placed in v2 subdirectory by mistake.
Florian Weimer Jan. 29, 2021, 8:56 a.m. UTC | #4 
* H. J. Lu:

> A v4 DSO may be placed in v2 subdirectory by mistake.

Right, and makes sense for ldconfig to warn about that.  But I don't see
why this data has to be stored in the cache separately, when it's
already implied by the subdirectory name.

Thanks,
Florian
H.J. Lu Jan. 29, 2021, 12:44 p.m. UTC | #5 
On Fri, Jan 29, 2021 at 12:56 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > A v4 DSO may be placed in v2 subdirectory by mistake.
>
> Right, and makes sense for ldconfig to warn about that.  But I don't see
> why this data has to be stored in the cache separately, when it's
> already implied by the subdirectory name.
>

With this patch:

diff --git a/elf/cache.c b/elf/cache.c
index c01d302072..ad644dae58 100644
--- a/elf/cache.c
+++ b/elf/cache.c
@@ -810,7 +810,7 @@ add_to_cache (const char *path, const char
*filename, const char *soname,
   new_entry->path = path_interned;
   new_entry->flags = flags;
   new_entry->osversion = osversion;
-  new_entry->isa_level = isa_level;
+  new_entry->isa_level = isa_level && 0;
   new_entry->hwcap = hwcap;
   new_entry->hwcaps = hwcaps;
   new_entry->bits_hwcap = 0;
@@ -982,7 +982,7 @@ insert_to_aux_cache (struct aux_cache_entry_id
*id, int flags,
   entry->id = *id;
   entry->flags = flags;
   entry->osversion = osversion;
-  entry->isa_level = isa_level;
+  entry->isa_level = isa_level && 0;
   entry->used = used;
   if (soname != NULL)
     entry->soname = memcpy ((char *) (entry + 1), soname, len);

I got

FAIL: elf/tst-glibc-hwcaps-2-cache

on Coffee Lake since the misplaced DSO is used.
diff mbox series

Patch

From f5053fabd1e8a5567b487ef4054793e043a7b817 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Sat, 5 Dec 2020 07:01:58 -0800
Subject: [PATCH] ldconfig/x86: Store ISA level in cache and aux cache

Store ISA level in the portion of the unused upper 32 bits of the hwcaps
field in cache and the unused pad field in aux cache.  ISA level is stored
and checked only for shared objects in glibc-hwcaps subdirectories.  The
shared objects in the default directories aren't checked since there are
no fallbacks for these shared objects.
---
 elf/cache.c                                   | 34 +++++---
 elf/dl-cache.c                                |  4 +
 elf/ldconfig.c                                | 18 +++--
 elf/readelflib.c                              | 81 ++++++++++++++++++-
 elf/readlib.c                                 |  7 +-
 elf/tst-glibc-hwcaps-2-cache.c                | 45 +++++++++++
 .../etc/ld.so.conf                            |  2 +
 .../postclean.req                             |  0
 elf/tst-glibc-hwcaps-2-cache.script           |  6 ++
 sysdeps/generic/dl-cache.h                    | 15 +++-
 sysdeps/generic/dl-isa-level.h                | 26 ++++++
 sysdeps/generic/ldconfig.h                    | 22 +++--
 sysdeps/generic/read-prop.h                   | 35 ++++++++
 sysdeps/unix/sysv/linux/arm/readelflib.c      | 22 ++---
 sysdeps/unix/sysv/linux/ia64/readelflib.c     | 22 ++---
 sysdeps/unix/sysv/linux/mips/readelflib.c     | 22 ++---
 sysdeps/unix/sysv/linux/powerpc/readelflib.c  | 22 ++---
 sysdeps/unix/sysv/linux/riscv/readelflib.c    | 22 ++---
 sysdeps/unix/sysv/linux/s390/readelflib.c     | 22 ++---
 sysdeps/unix/sysv/linux/sparc/readelflib.c    | 22 ++---
 sysdeps/unix/sysv/linux/x86/read-prop.h       | 61 ++++++++++++++
 sysdeps/unix/sysv/linux/x86/readelflib.c      | 23 +++---
 sysdeps/unix/sysv/linux/x86_64/Makefile       | 31 +++++++
 .../sysv/linux/x86_64/tst-glibc-hwcaps-2.c    | 61 ++++++++++++++
 .../linux/x86_64/x86-64-isa-level-VALUE.c     |  4 +
 sysdeps/x86/dl-isa-level.h                    | 32 ++++++++
 26 files changed, 550 insertions(+), 111 deletions(-)
 create mode 100644 elf/tst-glibc-hwcaps-2-cache.c
 create mode 100644 elf/tst-glibc-hwcaps-2-cache.root/etc/ld.so.conf
 create mode 100644 elf/tst-glibc-hwcaps-2-cache.root/postclean.req
 create mode 100644 elf/tst-glibc-hwcaps-2-cache.script
 create mode 100644 sysdeps/generic/dl-isa-level.h
 create mode 100644 sysdeps/generic/read-prop.h
 create mode 100644 sysdeps/unix/sysv/linux/x86/read-prop.h
 create mode 100644 sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c
 create mode 100644 sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
 create mode 100644 sysdeps/x86/dl-isa-level.h

diff --git a/elf/cache.c b/elf/cache.c
index b03c5319f8..91a72381ae 100644
--- a/elf/cache.c
+++ b/elf/cache.c
@@ -145,6 +145,7 @@  struct cache_entry
   struct stringtable_entry *path; /* Path to find library.  */
   int flags;			/* Flags to indicate kind of library.  */
   unsigned int osversion;	/* Required OS version.  */
+  unsigned int isa_level;	/* Required ISAL level.  */
   uint64_t hwcap;		/* Important hardware capabilities.  */
   int bits_hwcap;		/* Number of bits set in hwcap.  */
 
@@ -660,8 +661,14 @@  save_cache (const char *cache_name)
 	  if (entry->hwcaps == NULL)
 	    file_entries_new->libs[idx_new].hwcap = entry->hwcap;
 	  else
-	    file_entries_new->libs[idx_new].hwcap
-	      = DL_CACHE_HWCAP_EXTENSION | entry->hwcaps->section_index;
+	    {
+	      if (entry->isa_level > (1 << DL_CACHE_HWCAP_ISA_LEVEL_COUNT))
+		abort ();
+	      file_entries_new->libs[idx_new].hwcap
+		= (DL_CACHE_HWCAP_EXTENSION
+		   | (((uint64_t) entry->isa_level) << 32)
+		   | entry->hwcaps->section_index);
+	    }
 	  file_entries_new->libs[idx_new].key
 	    = str_offset + entry->lib->offset;
 	  file_entries_new->libs[idx_new].value
@@ -776,7 +783,8 @@  save_cache (const char *cache_name)
 /* Add one library to the cache.  */
 void
 add_to_cache (const char *path, const char *filename, const char *soname,
-	      int flags, unsigned int osversion, uint64_t hwcap,
+	      int flags, unsigned int osversion,
+	      unsigned int isa_level, uint64_t hwcap,
 	      struct glibc_hwcaps_subdirectory *hwcaps)
 {
   struct cache_entry *new_entry = xmalloc (sizeof (*new_entry));
@@ -794,6 +802,7 @@  add_to_cache (const char *path, const char *filename, const char *soname,
   new_entry->path = path_interned;
   new_entry->flags = flags;
   new_entry->osversion = osversion;
+  new_entry->isa_level = isa_level;
   new_entry->hwcap = hwcap;
   new_entry->hwcaps = hwcaps;
   new_entry->bits_hwcap = 0;
@@ -850,6 +859,7 @@  struct aux_cache_entry
   struct aux_cache_entry_id id;
   int flags;
   unsigned int osversion;
+  unsigned int isa_level;
   int used;
   char *soname;
   struct aux_cache_entry *next;
@@ -863,7 +873,7 @@  struct aux_cache_file_entry
   int32_t flags;		/* This is 1 for an ELF library.  */
   uint32_t soname;		/* String table indice.  */
   uint32_t osversion;		/* Required OS version.	 */
-  int32_t pad;
+  uint32_t isa_level;		/* Required ISA level.	 */
 };
 
 /* ldconfig maintains an auxiliary cache file that allows
@@ -914,7 +924,8 @@  init_aux_cache (void)
 
 int
 search_aux_cache (struct stat64 *stat_buf, int *flags,
-		  unsigned int *osversion, char **soname)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname)
 {
   struct aux_cache_entry_id id;
   id.ino = (uint64_t) stat_buf->st_ino;
@@ -932,6 +943,7 @@  search_aux_cache (struct stat64 *stat_buf, int *flags,
       {
 	*flags = entry->flags;
 	*osversion = entry->osversion;
+	*isa_level = entry->isa_level;
 	if (entry->soname != NULL)
 	  *soname = xstrdup (entry->soname);
 	else
@@ -945,7 +957,8 @@  search_aux_cache (struct stat64 *stat_buf, int *flags,
 
 static void
 insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
-		     unsigned int osversion, const char *soname, int used)
+		     unsigned int osversion, unsigned int isa_level,
+		     const char *soname, int used)
 {
   size_t hash = aux_cache_entry_id_hash (id) % aux_hash_size;
   struct aux_cache_entry *entry;
@@ -961,6 +974,7 @@  insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
   entry->id = *id;
   entry->flags = flags;
   entry->osversion = osversion;
+  entry->isa_level = isa_level;
   entry->used = used;
   if (soname != NULL)
     entry->soname = memcpy ((char *) (entry + 1), soname, len);
@@ -972,14 +986,15 @@  insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
 
 void
 add_to_aux_cache (struct stat64 *stat_buf, int flags,
-		  unsigned int osversion, const char *soname)
+		  unsigned int osversion, unsigned int isa_level,
+		  const char *soname)
 {
   struct aux_cache_entry_id id;
   id.ino = (uint64_t) stat_buf->st_ino;
   id.ctime = (uint64_t) stat_buf->st_ctime;
   id.size = (uint64_t) stat_buf->st_size;
   id.dev = (uint64_t) stat_buf->st_dev;
-  insert_to_aux_cache (&id, flags, osversion, soname, 1);
+  insert_to_aux_cache (&id, flags, osversion, isa_level, soname, 1);
 }
 
 /* Load auxiliary cache to search for unchanged entries.   */
@@ -1025,6 +1040,7 @@  load_aux_cache (const char *aux_cache_name)
     insert_to_aux_cache (&aux_cache->libs[i].id,
 			 aux_cache->libs[i].flags,
 			 aux_cache->libs[i].osversion,
+			 aux_cache->libs[i].isa_level,
 			 aux_cache->libs[i].soname == 0
 			 ? NULL : aux_cache_data + aux_cache->libs[i].soname,
 			 0);
@@ -1093,7 +1109,7 @@  save_aux_cache (const char *aux_cache_name)
 	      str_offset += len;
 	    }
 	  file_entries->libs[idx].osversion = entry->osversion;
-	  file_entries->libs[idx++].pad = 0;
+	  file_entries->libs[idx++].isa_level = entry->isa_level;
 	}
 
   /* Write out auxiliary cache file.  */
diff --git a/elf/dl-cache.c b/elf/dl-cache.c
index 97093bb700..edeff7ccc1 100644
--- a/elf/dl-cache.c
+++ b/elf/dl-cache.c
@@ -25,6 +25,7 @@ 
 #include <stdint.h>
 #include <_itoa.h>
 #include <dl-hwcaps.h>
+#include <dl-isa-level.h>
 
 #ifndef _DL_PLATFORMS_COUNT
 # define _DL_PLATFORMS_COUNT 0
@@ -284,6 +285,9 @@  search_cache (const char *string_table, uint32_t string_table_size,
 
 #ifdef SHARED
 			  named_hwcap = dl_cache_hwcap_extension (libnew);
+			  if (named_hwcap
+			      && !dl_cache_hwcap_isa_level_compatible (libnew))
+			    continue;
 #endif
 
 			  /* The entries with named/extension hwcaps
diff --git a/elf/ldconfig.c b/elf/ldconfig.c
index 10927a8c7f..9dceac38aa 100644
--- a/elf/ldconfig.c
+++ b/elf/ldconfig.c
@@ -655,6 +655,7 @@  manual_link (char *library)
   struct stat64 stat_buf;
   int flag;
   unsigned int osversion;
+  unsigned int isa_level;
 
   /* Prepare arguments for create_links call.  Split library name in
      directory and filename first.  Since path is allocated, we've got
@@ -721,7 +722,7 @@  manual_link (char *library)
     }
 
   if (process_file (real_library, library, libname, &flag, &osversion,
-		    &soname, 0, &stat_buf))
+		    &isa_level, &soname, 0, &stat_buf))
     {
       error (0, 0, _("No link created since soname could not be found for %s"),
 	     library);
@@ -768,6 +769,7 @@  struct dlib_entry
   int flag;
   int is_link;
   unsigned int osversion;
+  unsigned int isa_level;
   struct dlib_entry *next;
 };
 
@@ -980,17 +982,21 @@  search_dir (const struct dir_entry *entry)
 	 library already and it's not changed.  */
       char *soname;
       unsigned int osversion;
-      if (!search_aux_cache (&lstat_buf, &flag, &osversion, &soname))
+      unsigned int isa_level;
+      if (!search_aux_cache (&lstat_buf, &flag, &osversion, &isa_level,
+			     &soname))
 	{
 	  if (process_file (real_name, file_name, direntry->d_name, &flag,
-			    &osversion, &soname, is_link, &lstat_buf))
+			    &osversion, &isa_level, &soname, is_link,
+			    &lstat_buf))
 	    {
 	      if (real_name != real_file_name)
 		free (real_name);
 	      continue;
 	    }
 	  else if (opt_build_cache)
-	    add_to_aux_cache (&lstat_buf, flag, osversion, soname);
+	    add_to_aux_cache (&lstat_buf, flag, osversion, isa_level,
+			      soname);
 	}
 
       if (soname == NULL)
@@ -1096,6 +1102,7 @@  search_dir (const struct dir_entry *entry)
 		  dlib_ptr->name = xstrdup (direntry->d_name);
 		  dlib_ptr->is_link = is_link;
 		  dlib_ptr->osversion = osversion;
+		  dlib_ptr->isa_level = isa_level;
 		}
 	      /* Don't add this library, abort loop.  */
 	      /* Also free soname, since it's dynamically allocated.  */
@@ -1112,6 +1119,7 @@  search_dir (const struct dir_entry *entry)
 	  dlib_ptr->flag = flag;
 	  dlib_ptr->is_link = is_link;
 	  dlib_ptr->osversion = osversion;
+	  dlib_ptr->isa_level = isa_level;
 	  /* Add at head of list.  */
 	  dlib_ptr->next = dlibs;
 	  dlibs = dlib_ptr;
@@ -1149,7 +1157,7 @@  search_dir (const struct dir_entry *entry)
       if (opt_build_cache)
 	add_to_cache (entry->path, filename, dlib_ptr->soname,
 		      dlib_ptr->flag, dlib_ptr->osversion,
-		      hwcap, entry->hwcaps);
+		      dlib_ptr->isa_level, hwcap, entry->hwcaps);
     }
 
   /* Free all resources.  */
diff --git a/elf/readelflib.c b/elf/readelflib.c
index 5905f6d344..abb1ac61fa 100644
--- a/elf/readelflib.c
+++ b/elf/readelflib.c
@@ -17,6 +17,8 @@ 
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+#include <read-prop.h>
+
 /* This code is a heavily simplified version of the readelf program
    that's part of the current binutils development version.  For architectures
    which need to handle both 32bit and 64bit ELF libraries,  this file is
@@ -40,8 +42,8 @@  do								\
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname, void *file_contents, size_t file_length)
 {
   int i;
   unsigned int j;
@@ -86,6 +88,9 @@  process_elf_file (const char *file_name, const char *lib, int *flag,
      libc5/libc6.  */
   *flag = FLAG_ELF;
 
+  /* The default ISA level is 0.  */
+  *isa_level = 0;
+
   dynamic_addr = 0;
   dynamic_size = 0;
   program_interpreter = NULL;
@@ -164,6 +169,78 @@  process_elf_file (const char *file_name, const char *lib, int *flag,
 	    }
 	  break;
 
+	case PT_GNU_PROPERTY:
+	  /* The NT_GNU_PROPERTY_TYPE_0 note must be aligned to 4 bytes
+	     in 32-bit objects and to 8 bytes in 64-bit objects.  Skip
+	     notes with incorrect alignment.  */
+	  if (segment->p_align == (__ELF_NATIVE_CLASS / 8))
+	    {
+	      const ElfW(Nhdr) *note = (const void *) (file_contents
+						       + segment->p_offset);
+	      const ElfW(Addr) size = segment->p_filesz;
+	      const ElfW(Addr) align = segment->p_align;
+
+	      const ElfW(Addr) start = (ElfW(Addr)) (uintptr_t) note;
+	      unsigned int last_type = 0;
+
+	      while ((ElfW(Addr)) (uintptr_t) (note + 1) - start < size)
+		{
+		  /* Find the NT_GNU_PROPERTY_TYPE_0 note.  */
+		  if (note->n_namesz == 4
+		      && note->n_type == NT_GNU_PROPERTY_TYPE_0
+		      && memcmp (note + 1, "GNU", 4) == 0)
+		    {
+		      /* Check for invalid property.  */
+		      if (note->n_descsz < 8
+			  || (note->n_descsz % sizeof (ElfW(Addr))) != 0)
+			goto done;
+
+		      /* Start and end of property array.  */
+		      unsigned char *ptr = (unsigned char *) (note + 1) + 4;
+		      unsigned char *ptr_end = ptr + note->n_descsz;
+
+		      do
+			{
+			  unsigned int type = *(unsigned int *) ptr;
+			  unsigned int datasz = *(unsigned int *) (ptr + 4);
+
+			  /* Property type must be in ascending order.  */
+			  if (type < last_type)
+			    goto done;
+
+			  ptr += 8;
+			  if ((ptr + datasz) > ptr_end)
+			    goto done;
+
+			  last_type = type;
+
+			  /* Target specific property processing.
+			     Return value:
+			       false: Continue processing the properties.
+			       true : Stop processing the properties.
+			   */
+			  if (read_gnu_property (isa_level, type,
+						 datasz, ptr))
+			    goto done;
+
+			  /* Check the next property item.  */
+			  ptr += ALIGN_UP (datasz, sizeof (ElfW(Addr)));
+			}
+		      while ((ptr_end - ptr) >= 8);
+
+		      /* Only handle one NT_GNU_PROPERTY_TYPE_0.  */
+		      goto done;
+		    }
+
+		  note = ((const void *) note
+			  + ELF_NOTE_NEXT_OFFSET (note->n_namesz,
+						  note->n_descsz,
+						  align));
+		}
+	    }
+done:
+	  break;
+
 	default:
 	  break;
 	}
diff --git a/elf/readlib.c b/elf/readlib.c
index 994a4426a1..def0eafbeb 100644
--- a/elf/readlib.c
+++ b/elf/readlib.c
@@ -75,7 +75,8 @@  is_gdb_python_file (const char *name)
 int
 process_file (const char *real_file_name, const char *file_name,
 	      const char *lib, int *flag, unsigned int *osversion,
-	      char **soname, int is_link, struct stat64 *stat_buf)
+	      unsigned int *isa_level, char **soname, int is_link,
+	      struct stat64 *stat_buf)
 {
   FILE *file;
   struct stat64 statbuf;
@@ -173,8 +174,8 @@  process_file (const char *real_file_name, const char *file_name,
   /* Libraries have to be shared object files.  */
   else if (elf_header->e_type != ET_DYN)
     ret = 1;
-  else if (process_elf_file (file_name, lib, flag, osversion, soname,
-			     file_contents, statbuf.st_size))
+  else if (process_elf_file (file_name, lib, flag, osversion, isa_level,
+			     soname, file_contents, statbuf.st_size))
     ret = 1;
 
  done:
diff --git a/elf/tst-glibc-hwcaps-2-cache.c b/elf/tst-glibc-hwcaps-2-cache.c
new file mode 100644
index 0000000000..2c30a2c911
--- /dev/null
+++ b/elf/tst-glibc-hwcaps-2-cache.c
@@ -0,0 +1,45 @@ 
+/* Wrapper to invoke tst-glibc-hwcaps-2 in a container to test ldconfig.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* This program is just a wrapper that runs ldconfig followed by
+   tst-glibc-hwcaps-2.  The actual test is provided via an
+   implementation in a sysdeps subdirectory.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/support.h>
+#include <unistd.h>
+
+int
+main (int argc, char **argv)
+{
+  /* Run ldconfig to populate the cache.  */
+  {
+    char *command = xasprintf ("%s/ldconfig", support_install_rootsbindir);
+    if (system (command) != 0)
+      return 1;
+    free (command);
+  }
+
+  /* Reuse tst-glibc-hwcaps.  Since this code is running in a
+     container, we can launch it directly.  */
+  char *path = xasprintf ("%s/elf/tst-glibc-hwcaps-2", support_objdir_root);
+  execv (path, argv);
+  printf ("error: execv of %s failed: %m\n", path);
+  return 1;
+}
diff --git a/elf/tst-glibc-hwcaps-2-cache.root/etc/ld.so.conf b/elf/tst-glibc-hwcaps-2-cache.root/etc/ld.so.conf
new file mode 100644
index 0000000000..e1e74dbda2
--- /dev/null
+++ b/elf/tst-glibc-hwcaps-2-cache.root/etc/ld.so.conf
@@ -0,0 +1,2 @@ 
+# This file was created to suppress a warning from ldconfig:
+# /sbin/ldconfig: Warning: ignoring configuration file that cannot be opened: /etc/ld.so.conf: No such file or directory
diff --git a/elf/tst-glibc-hwcaps-2-cache.root/postclean.req b/elf/tst-glibc-hwcaps-2-cache.root/postclean.req
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/elf/tst-glibc-hwcaps-2-cache.script b/elf/tst-glibc-hwcaps-2-cache.script
new file mode 100644
index 0000000000..29ccfc3b49
--- /dev/null
+++ b/elf/tst-glibc-hwcaps-2-cache.script
@@ -0,0 +1,6 @@ 
+# test-container does not support scripts in sysdeps directories, so
+# collect everything in one file.
+
+mkdirp 0770 $L/glibc-hwcaps/x86-64-v2
+cp $B/elf/libx86-64-isa-level-1.so $L/libx86-64-isa-level.so
+cp $B/elf/libx86-64-isa-level-4.so $L/glibc-hwcaps/x86-64-v2/libx86-64-isa-level.so
diff --git a/sysdeps/generic/dl-cache.h b/sysdeps/generic/dl-cache.h
index 72a66b45ee..1138228e5c 100644
--- a/sysdeps/generic/dl-cache.h
+++ b/sysdeps/generic/dl-cache.h
@@ -106,14 +106,23 @@  struct file_entry_new
    entries.  */
 #define DL_CACHE_HWCAP_EXTENSION (1ULL << 62)
 
+/* The number of the ISA level bits in the upper 32 bits of the hwcap
+   field.  */
+#define DL_CACHE_HWCAP_ISA_LEVEL_COUNT 10
+
+/* The mask of the ISA level bits in the hwcap field.  */
+#define DL_CACHE_HWCAP_ISA_LEVEL_MASK \
+  ((1 << DL_CACHE_HWCAP_ISA_LEVEL_COUNT) -1)
+
 /* Return true if the ENTRY->hwcap value indicates that
    DL_CACHE_HWCAP_EXTENSION is used.  */
 static inline bool
 dl_cache_hwcap_extension (struct file_entry_new *entry)
 {
-  /* If DL_CACHE_HWCAP_EXTENSION is set, but other bits as well, this
-     is a different kind of extension.  */
-  return (entry->hwcap >> 32) == (DL_CACHE_HWCAP_EXTENSION >> 32);
+  /* If DL_CACHE_HWCAP_EXTENSION is set, but other bits, except for the
+     ISA level bits, as well, this is a different kind of extension.  */
+  return (((entry->hwcap >> 32) & ~DL_CACHE_HWCAP_ISA_LEVEL_MASK)
+	  == (DL_CACHE_HWCAP_EXTENSION >> 32));
 }
 
 /* See flags member of struct cache_file_new below.  */
diff --git a/sysdeps/generic/dl-isa-level.h b/sysdeps/generic/dl-isa-level.h
new file mode 100644
index 0000000000..77735775b9
--- /dev/null
+++ b/sysdeps/generic/dl-isa-level.h
@@ -0,0 +1,26 @@ 
+/* Support for reading ISA level in /etc/ld.so.cache files written by
+   Linux ldconfig.  Generic version.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* Return true if the ISA level in ENTRY is compatible with CPU.  */
+
+static inline bool
+dl_cache_hwcap_isa_level_compatible (struct file_entry_new *entry)
+{
+  return true;
+}
diff --git a/sysdeps/generic/ldconfig.h b/sysdeps/generic/ldconfig.h
index 1ad1528890..a5ed350237 100644
--- a/sysdeps/generic/ldconfig.h
+++ b/sysdeps/generic/ldconfig.h
@@ -70,8 +70,9 @@  const char *glibc_hwcaps_subdirectory_name
   (const struct glibc_hwcaps_subdirectory *);
 
 extern void add_to_cache (const char *path, const char *filename,
-			  const char *soname,
-			  int flags, unsigned int osversion, uint64_t hwcap,
+			  const char *soname, int flags,
+			  unsigned int osversion, unsigned int isa_level,
+			  uint64_t hwcap,
 			  struct glibc_hwcaps_subdirectory *);
 
 extern void init_aux_cache (void);
@@ -79,23 +80,28 @@  extern void init_aux_cache (void);
 extern void load_aux_cache (const char *aux_cache_name);
 
 extern int search_aux_cache (struct stat64 *stat_buf, int *flags,
-			     unsigned int *osversion, char **soname);
+			     unsigned int *osversion,
+			     unsigned int *isa_level, char **soname);
 
 extern void add_to_aux_cache (struct stat64 *stat_buf, int flags,
-			      unsigned int osversion, const char *soname);
+			      unsigned int osversion,
+			      unsigned int isa_level, const char *soname);
 
 extern void save_aux_cache (const char *aux_cache_name);
 
 /* Declared in readlib.c.  */
 extern int process_file (const char *real_file_name, const char *file_name,
-			 const char *lib, int *flag, unsigned int *osversion,
-			 char **soname, int is_link, struct stat64 *stat_buf);
+			 const char *lib, int *flag,
+			 unsigned int *osversion, unsigned int *isa_level,
+			 char **soname, int is_link,
+			 struct stat64 *stat_buf);
 
 extern char *implicit_soname (const char *lib, int flag);
 
 /* Declared in readelflib.c.  */
-extern int process_elf_file (const char *file_name, const char *lib, int *flag,
-			     unsigned int *osversion, char **soname,
+extern int process_elf_file (const char *file_name, const char *lib,
+			     int *flag, unsigned int *osversion,
+			     unsigned int *isa_level, char **soname,
 			     void *file_contents, size_t file_length);
 
 /* Declared in chroot_canon.c.  */
diff --git a/sysdeps/generic/read-prop.h b/sysdeps/generic/read-prop.h
new file mode 100644
index 0000000000..091bd2f6c1
--- /dev/null
+++ b/sysdeps/generic/read-prop.h
@@ -0,0 +1,35 @@ 
+/* Support for GNU properties in ldconfig.  Generic version.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _READ_PROP_H
+#define _READ_PROP_H
+
+/* Called for each property in the NT_GNU_PROPERTY_TYPE_0 note of SEGMENT.
+   Return value:
+     false: Continue processing the properties.
+     true : Stop processing the properties.
+ */
+
+static inline bool __attribute__ ((always_inline))
+read_gnu_property (unsigned int *isal_level, uint32_t type, uint32_t
+		   datasz, void *data)
+{
+  return true;
+}
+
+#endif
diff --git a/sysdeps/unix/sysv/linux/arm/readelflib.c b/sysdeps/unix/sysv/linux/arm/readelflib.c
index 9d03fa6405..7f444add14 100644
--- a/sysdeps/unix/sysv/linux/arm/readelflib.c
+++ b/sysdeps/unix/sysv/linux/arm/readelflib.c
@@ -18,18 +18,20 @@ 
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
@@ -38,8 +40,8 @@  process_elf_file (const char *file_name, const char *lib, int *flag,
     {
       Elf32_Ehdr *elf32_header = (Elf32_Ehdr *) elf_header;
 
-      ret = process_elf32_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
 
       if (!ret && EF_ARM_EABI_VERSION (elf32_header->e_flags) == EF_ARM_EABI_VER5)
 	{
@@ -57,8 +59,8 @@  process_elf_file (const char *file_name, const char *lib, int *flag,
     }
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* AArch64 libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_AARCH64_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/ia64/readelflib.c b/sysdeps/unix/sysv/linux/ia64/readelflib.c
index d24a934351..19d37b438e 100644
--- a/sysdeps/unix/sysv/linux/ia64/readelflib.c
+++ b/sysdeps/unix/sysv/linux/ia64/readelflib.c
@@ -16,29 +16,31 @@ 
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname,
-		  void *file_contents, size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
-    return process_elf32_file (file_name, lib, flag, osversion, soname,
-			       file_contents, file_length);
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* Intel 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_IA64_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/mips/readelflib.c b/sysdeps/unix/sysv/linux/mips/readelflib.c
index 8363b8afcc..a3399961c9 100644
--- a/sysdeps/unix/sysv/linux/mips/readelflib.c
+++ b/sysdeps/unix/sysv/linux/mips/readelflib.c
@@ -20,18 +20,20 @@ 
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname, void *file_contents, size_t file_length)
 {
   union
     {
@@ -45,8 +47,8 @@  process_elf_file (const char *file_name, const char *lib, int *flag,
   elf_header.eh = file_contents;
   if (elf_header.eh->e_ident [EI_CLASS] == ELFCLASS32)
     {
-      ret = process_elf32_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       if (!ret)
 	{
 	  Elf32_Word flags = elf_header.eh32->e_flags;
@@ -62,8 +64,8 @@  process_elf_file (const char *file_name, const char *lib, int *flag,
     }
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* n64 libraries are always libc.so.6+.  */
       if (!ret)
 	{
diff --git a/sysdeps/unix/sysv/linux/powerpc/readelflib.c b/sysdeps/unix/sysv/linux/powerpc/readelflib.c
index eb20680418..ce01658fb3 100644
--- a/sysdeps/unix/sysv/linux/powerpc/readelflib.c
+++ b/sysdeps/unix/sysv/linux/powerpc/readelflib.c
@@ -17,29 +17,31 @@ 
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
-    return process_elf32_file (file_name, lib, flag, osversion, soname,
-			       file_contents, file_length);
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* PowerPC 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_POWERPC_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/riscv/readelflib.c b/sysdeps/unix/sysv/linux/riscv/readelflib.c
index 1e70735cc0..98ae3c0b2b 100644
--- a/sysdeps/unix/sysv/linux/riscv/readelflib.c
+++ b/sysdeps/unix/sysv/linux/riscv/readelflib.c
@@ -17,11 +17,13 @@ 
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* The ELF flags supported by our current glibc port:
@@ -38,8 +40,8 @@  int process_elf64_file (const char *file_name, const char *lib, int *flag,
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   Elf32_Ehdr *elf32_header = (Elf32_Ehdr *) elf_header;
@@ -52,14 +54,14 @@  process_elf_file (const char *file_name, const char *lib, int *flag,
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
     {
-      ret = process_elf32_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       flags = elf32_header->e_flags;
     }
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       flags = elf64_header->e_flags;
     }
 
diff --git a/sysdeps/unix/sysv/linux/s390/readelflib.c b/sysdeps/unix/sysv/linux/s390/readelflib.c
index 1718efc9f9..6d19e351ba 100644
--- a/sysdeps/unix/sysv/linux/s390/readelflib.c
+++ b/sysdeps/unix/sysv/linux/s390/readelflib.c
@@ -16,29 +16,31 @@ 
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
-    return process_elf32_file (file_name, lib, flag, osversion, soname,
-			       file_contents, file_length);
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* S/390 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_S390_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/sparc/readelflib.c b/sysdeps/unix/sysv/linux/sparc/readelflib.c
index e027a11a37..3768003925 100644
--- a/sysdeps/unix/sysv/linux/sparc/readelflib.c
+++ b/sysdeps/unix/sysv/linux/sparc/readelflib.c
@@ -18,29 +18,31 @@ 
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
-    return process_elf32_file (file_name, lib, flag, osversion, soname,
-			       file_contents, file_length);
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* Sparc 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_SPARC_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/x86/read-prop.h b/sysdeps/unix/sysv/linux/x86/read-prop.h
new file mode 100644
index 0000000000..ac37fbc449
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86/read-prop.h
@@ -0,0 +1,61 @@ 
+/* Support for GNU properties in ldconfig.  x86 version.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _READ_PROP_H
+#define _READ_PROP_H
+
+#include <dl-cache.h>
+
+/* Called for each property in the NT_GNU_PROPERTY_TYPE_0 note of SEGMENT.
+   Return value:
+     false: Continue processing the properties.
+     true : Stop processing the properties.
+ */
+
+static inline bool __attribute__ ((always_inline))
+read_gnu_property (unsigned int *isal_level, uint32_t type,
+		   uint32_t datasz, void *data)
+{
+  /* Property type must be in ascending order.  */
+  if (type > GNU_PROPERTY_X86_ISA_1_NEEDED)
+    return true;
+
+  if (type == GNU_PROPERTY_X86_ISA_1_NEEDED)
+    {
+      if (datasz == 4)
+	{
+	  /* The size of GNU_PROPERTY_X86_ISA_1_NEEDED must be 4 bytes.
+	     There is no point to continue if this type is ill-formed.  */
+	  unsigned int isa_1_needed = *(unsigned int *) data;
+	  _Static_assert (((sizeof (isa_1_needed) * 8)
+			   <= (1 << DL_CACHE_HWCAP_ISA_LEVEL_COUNT)),
+			  "DL_CACHE_HWCAP_ISA_LEVEL_COUNT is too small");
+	  if (isa_1_needed)
+	    {
+	      unsigned int level;
+	      asm ("bsr %1, %0" : "=r" (level) : "g" (isa_1_needed));
+	      *isal_level = level;
+	    }
+	}
+      return true;
+    }
+
+  return false;
+}
+
+#endif
diff --git a/sysdeps/unix/sysv/linux/x86/readelflib.c b/sysdeps/unix/sysv/linux/x86/readelflib.c
index 3e83419f5b..716629bf10 100644
--- a/sysdeps/unix/sysv/linux/x86/readelflib.c
+++ b/sysdeps/unix/sysv/linux/x86/readelflib.c
@@ -17,19 +17,20 @@ 
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret, file_flag = 0;
@@ -68,11 +69,11 @@  failed:
     }
 
   if (elf_header->e_ident[EI_CLASS] == ELFCLASS32)
-    ret = process_elf32_file (file_name, lib, flag, osversion, soname,
-			      file_contents, file_length);
+    ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			      soname, file_contents, file_length);
   else
-    ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-			      file_contents, file_length);
+    ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+			      soname, file_contents, file_length);
 
   if (!ret && file_flag)
     *flag = file_flag;
diff --git a/sysdeps/unix/sysv/linux/x86_64/Makefile b/sysdeps/unix/sysv/linux/x86_64/Makefile
index 9b82155393..9a7b3cd8e5 100644
--- a/sysdeps/unix/sysv/linux/x86_64/Makefile
+++ b/sysdeps/unix/sysv/linux/x86_64/Makefile
@@ -13,3 +13,34 @@  endif
 ifeq ($(subdir),misc)
 gen-as-const-headers += sigaltstack-offsets.sym
 endif
+
+ifeq ($(subdir),elf)
+ifeq (yesyes,$(enable-x86-isa-level)$(config-cflags-skylake-avx512))
+tests += tst-glibc-hwcaps-2
+ifeq (no,$(build-hardcoded-path-in-tests))
+# This is an ld.so.cache test, and RPATH/RUNPATH in the executable
+# interferes with its test objectives.
+tests-container += tst-glibc-hwcaps-2-cache
+endif
+modules-names += libx86-64-isa-level-1 libx86-64-isa-level-4
+
+$(objpfx)tst-glibc-hwcaps-2: $(objpfx)libx86-64-isa-level.so
+
+$(objpfx)tst-glibc-hwcaps-2.out: \
+  $(objpfx)glibc-hwcaps/x86-64-v4/libx86-64-isa-level.so
+$(objpfx)glibc-hwcaps/x86-64-v4/libx86-64-isa-level.so: \
+  $(objpfx)libx86-64-isa-level-4.so
+	cp $< $@
+
+CFLAGS-libx86-64-isa-level-1.os += -march=x86-64
+CFLAGS-libx86-64-isa-level-4.os += -march=skylake-avx512
+
+# The test modules are parameterized by preprocessor macros.
+LDFLAGS-libx86-64-isa-level-1.so += -Wl,-soname,libx86-64-isa-level.so
+LDFLAGS-libx86-64-isa-level-4.so += -Wl,-soname,libx86-64-isa-level.so
+$(objpfx)libx86-64-isa-level%.os: $(..)/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
+	$(compile-command.c) -DVALUE=$(lastword $(subst -, ,$*))
+$(objpfx)libx86-64-isa-level.so: $(objpfx)libx86-64-isa-level-1.so
+	cp $< $@
+endif
+endif # $(subdir) == elf
diff --git a/sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c b/sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c
new file mode 100644
index 0000000000..8d6b17d658
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c
@@ -0,0 +1,61 @@ 
+/* Check ISA level on shared object in glibc-hwcaps subdirectories.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <elf.h>
+#include <get-isa-level.h>
+#include <support/check.h>
+#include <support/test-driver.h>
+
+extern int dso_isa_level (void);
+
+static int
+do_test (void)
+{
+  const struct cpu_features *cpu_features
+    = __x86_get_cpu_features (COMMON_CPUID_INDEX_MAX);
+  unsigned int isa_level = get_isa_level (cpu_features);
+  int level = dso_isa_level ();
+  int ret;
+  switch (level)
+    {
+    case 1:
+      /* The default libx86-64-isa-level.so should be used.  */
+      printf ("The default shared library is used.\n");
+      if ((isa_level & GNU_PROPERTY_X86_ISA_1_V4) != 0)
+	ret = EXIT_FAILURE;
+      else
+	ret = EXIT_SUCCESS;
+      break;
+    case 4:
+      /* libx86-64-isa-level.so marked as x86-64 ISA level 4 needed in
+	 x86-64-v2 should be ignored on lesser CPU.  */
+      printf ("x86-64 ISA level 4 shared library in x86-64-v2 is used.\n");
+      if ((isa_level & GNU_PROPERTY_X86_ISA_1_V4) != 0)
+	ret = EXIT_SUCCESS;
+      else
+	ret = EXIT_FAILURE;
+      break;
+    default:
+      abort ();
+    }
+  return ret;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c b/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
new file mode 100644
index 0000000000..2813d627cc
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
@@ -0,0 +1,4 @@ 
+#define INCLUDE_X86_ISA_LEVEL
+#define MARKER dso_isa_level
+#include <isa-level.c>
+#include <markermodMARKER-VALUE.c>
diff --git a/sysdeps/x86/dl-isa-level.h b/sysdeps/x86/dl-isa-level.h
new file mode 100644
index 0000000000..c6ed8fb9d2
--- /dev/null
+++ b/sysdeps/x86/dl-isa-level.h
@@ -0,0 +1,32 @@ 
+/* Support for reading ISA level in /etc/ld.so.cache files written by
+   Linux ldconfig.  x86 version.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sys/platform/x86.h>
+
+/* Return true if the ISA level in ENTRY is compatible with CPU.  */
+
+static inline bool
+dl_cache_hwcap_isa_level_compatible (struct file_entry_new *entry)
+{
+  const struct cpu_features *cpu_features = __get_cpu_features ();
+  unsigned int isa_level
+    = 1 << ((entry->hwcap >> 32) & DL_CACHE_HWCAP_ISA_LEVEL_MASK);
+
+  return (isa_level & cpu_features->isa_1) == isa_level;
+}
-- 
2.29.2