[v2,3/3] elf: Remove LD_USE_LOAD_BIAS

  It is solely for prelink with PIE exectuables [1].

[1] https://sourceware.org/legacy-ml/libc-hacker/2003-11/msg00127.html
---
 NEWS                        |  3 +++
 elf/dl-map-segments.h       |  3 +--
 elf/dl-support.c            |  1 -
 elf/rtld.c                  | 13 -------------
 sysdeps/generic/ldsodefs.h  |  5 -----
 sysdeps/generic/unsecvars.h |  1 -
 6 files changed, 4 insertions(+), 22 deletions(-)
  

On 04/02/2022 00:27, Adhemerval Zanella via Libc-alpha wrote:
> It is solely for prelink with PIE exectuables [1].
> 
> [1] https://sourceware.org/legacy-ml/libc-hacker/2003-11/msg00127.html

LGTM.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

> ---
>   NEWS                        |  3 +++
>   elf/dl-map-segments.h       |  3 +--
>   elf/dl-support.c            |  1 -
>   elf/rtld.c                  | 13 -------------
>   sysdeps/generic/ldsodefs.h  |  5 -----
>   sysdeps/generic/unsecvars.h |  1 -
>   6 files changed, 4 insertions(+), 22 deletions(-)
> 
> diff --git a/NEWS b/NEWS
> index f9c4589037..b1540ba583 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -196,6 +196,9 @@ Deprecated and removed features, and other changes affecting compatibility:
>     functionality to obtain the program mapping address can be achieved by
>     using LD_TRACE_LOADED_OBJECTS to value of 2.
>   
> +* The LD_USE_LOAD_BIAS has been removed.  The variable was mainly used to
> +  support prelink PIE binaries.
> +
>   Changes to build and runtime requirements:
>   
>   * The audit module interface version LAV_CURRENT is increased to enable
> diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
> index 172692b120..b3513e7909 100644
> --- a/elf/dl-map-segments.h
> +++ b/elf/dl-map-segments.h
> @@ -94,8 +94,7 @@ _dl_map_segments (struct link_map *l, int fd,
>            prefer to map such objects at; but this is only a preference,
>            the OS can do whatever it likes. */
>         ElfW(Addr) mappref
> -        = (ELF_PREFERRED_ADDRESS (loader, maplength,
> -                                  c->mapstart & GLRO(dl_use_load_bias))
> +        = (ELF_PREFERRED_ADDRESS (loader, maplength, c->mapstart)
>              - MAP_BASE_ADDR (l));
>   
>         /* Remember which part of the address space this object uses.  */
> diff --git a/elf/dl-support.c b/elf/dl-support.c
> index fb64765537..6d2c4baf81 100644
> --- a/elf/dl-support.c
> +++ b/elf/dl-support.c
> @@ -54,7 +54,6 @@ size_t _dl_platformlen;
>   
>   int _dl_debug_mask;
>   int _dl_lazy;
> -ElfW(Addr) _dl_use_load_bias = -2;
>   int _dl_dynamic_weak;
>   
>   /* If nonzero print warnings about problematic situations.  */
> diff --git a/elf/rtld.c b/elf/rtld.c
> index aa18256d86..19e328f89e 100644
> --- a/elf/rtld.c
> +++ b/elf/rtld.c
> @@ -365,7 +365,6 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
>       ._dl_sysinfo = DL_SYSINFO_DEFAULT,
>   #endif
>       ._dl_debug_fd = STDERR_FILENO,
> -    ._dl_use_load_bias = -2,
>       ._dl_correct_cache_id = _DL_CACHE_DEFAULT_ID,
>   #if !HAVE_TUNABLES
>       ._dl_hwcap_mask = HWCAP_IMPORTANT,
> @@ -1742,12 +1741,6 @@ dl_main (const ElfW(Phdr) *phdr,
>     ++GL(dl_ns)[LM_ID_BASE]._ns_nloaded;
>     ++GL(dl_load_adds);
>   
> -  /* If LD_USE_LOAD_BIAS env variable has not been seen, default
> -     to not using bias for non-prelinked PIEs and libraries
> -     and using it for executables or prelinked PIEs or libraries.  */
> -  if (GLRO(dl_use_load_bias) == (ElfW(Addr)) -2)
> -    GLRO(dl_use_load_bias) = main_map->l_addr == 0 ? -1 : 0;
> -
>     /* Starting from binutils-2.23, the linker will define the magic symbol
>        __ehdr_start to point to our own ELF header if it is visible in a
>        segment that also includes the phdrs.  If that's not available, we use
> @@ -2657,12 +2650,6 @@ process_envvars (struct dl_main_state *state)
>   #ifdef EXTRA_LD_ENVVARS_13
>   	  EXTRA_LD_ENVVARS_13
>   #endif
> -	  if (!__libc_enable_secure
> -	      && memcmp (envline, "USE_LOAD_BIAS", 13) == 0)
> -	    {
> -	      GLRO(dl_use_load_bias) = envline[14] == '1' ? -1 : 0;
> -	      break;
> -	    }
>   	  break;
>   
>   	case 14:
> diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
> index d1c6cd902b..9878e7e87e 100644
> --- a/sysdeps/generic/ldsodefs.h
> +++ b/sysdeps/generic/ldsodefs.h
> @@ -628,11 +628,6 @@ struct rtld_global_ro
>     /* Location of the binary.  */
>     EXTERN const char *_dl_origin_path;
>   
> -  /* -1 if the dynamic linker should honor library load bias,
> -     0 if not, -2 use the default (honor biases for normal
> -     binaries, don't honor for PIEs).  */
> -  EXTERN ElfW(Addr) _dl_use_load_bias;
> -
>     /* Size of the static TLS block.  */
>     EXTERN size_t _dl_tls_static_size;
>   
> diff --git a/sysdeps/generic/unsecvars.h b/sysdeps/generic/unsecvars.h
> index 5ea8a4a259..b50331b50f 100644
> --- a/sysdeps/generic/unsecvars.h
> +++ b/sysdeps/generic/unsecvars.h
> @@ -22,7 +22,6 @@
>     "LD_PRELOAD\0"							      \
>     "LD_PROFILE\0"							      \
>     "LD_SHOW_AUXV\0"							      \
> -  "LD_USE_LOAD_BIAS\0"							      \
>     "LOCALDOMAIN\0"							      \
>     "LOCPATH\0"								      \
>     "MALLOC_TRACE\0"							      \