[4/4] libgcc: Use _dl_find_eh_frame in _Unwind_Find_FDE

  libgcc/ChangeLog

	* unwind-dw2-fde-dip.c (USE_DL_FIND_EH_FRAME)
	(DL_FIND_EH_FRAME_CONDITION): New macros.
	[__GLIBC__ && !DL_FIND_EH_FRAME_DBASE] (_dl_find_eh_frame):
	Declare weak function.
	(_Unwind_Find_FDE): Call _dl_find_eh_frame if available.
---
 libgcc/unwind-dw2-fde-dip.c | 50 +++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
  

On Wed, Nov 03, 2021 at 05:28:55PM +0100, Florian Weimer wrote:
> --- a/libgcc/unwind-dw2-fde-dip.c
> +++ b/libgcc/unwind-dw2-fde-dip.c
> @@ -129,6 +129,30 @@ unw_eh_callback_data_dbase (const struct unw_eh_callback_data *data
>  #endif
>  }
>  
> +#ifdef DL_FIND_EH_FRAME_DBASE
> +#if DL_FIND_EH_FRAME_DBASE != NEED_DBASE_MEMBER
> +#error "DL_FIND_EH_FRAME_DBASE != NEED_DBASE_MEMBER"

Instead of #error just don't define USE_DL_FIND_EH_FRAME?
I.e.
#ifdef DL_FIND_EH_FRAME_DBASE
#if DL_FIND_EH_FRAME_DBASE == NEED_DBASE_MEMBER
> +#define USE_DL_FIND_EH_FRAME 1
> +#define DL_FIND_EH_FRAME_CONDITION 1
> +#endif
?
Is it a good idea to have different arguments of the function for
i386/nios2/frv/bfind vs. the rest, wouldn't just always passing void **__dbase
argument be cleaner?
Internally it is fine to differentiate based on NEED_DBASE_MEMBER, but doing
that on a public interface?

> +/* Fallback declaration for old glibc headers.  DL_FIND_EH_FRAME_DBASE is used
> +   as a proxy to determine if <dlfcn.h> declares _dl_find_eh_frame.  */
> +#if defined __GLIBC__ && !defined DL_FIND_EH_FRAME_DBASE
> +#if NEED_DBASE_MEMBER
> +void *_dl_find_eh_frame (void *__pc, void **__dbase) __attribute__ ((weak));
> +#else
> +void *_dl_find_eh_frame (void *__pc) __attribute__ ((weak));
> +#endif
> +#define USE_DL_FIND_EH_FRAME 1
> +#define DL_FIND_EH_FRAME_CONDITION (_dl_find_eh_frame != NULL)
> +#endif

I'd prefer not to do this.  If we find glibc with the support in the
headers, let's use it, otherwise let's keep using what we were doing before.

> +#if NEED_DBASE_MEMBER
> +      eh_frame = _dl_find_eh_frame (pc, &dbase);
> +#else
> +      dbase = NULL;
> +      eh_frame = _dl_find_eh_frame (pc);
> +#endif
> +      if (eh_frame == NULL)
> +	return NULL;
> +
> +      struct find_fde_tail_result result
> +	= find_fde_tail ((_Unwind_Ptr) pc, eh_frame, (_Unwind_Ptr) dbase);
> +      if (result.entry != NULL)
> +	{
> +	  bases->tbase = NULL;
> +	  bases->dbase = (void *) dbase;
> +	  bases->func = result.func;
> +	}
> +      return result.entry;
> +    }
> +#endif
> +
>    data.pc = (_Unwind_Ptr) pc;
>  #if NEED_DBASE_MEMBER
>    data.dbase = NULL;
> -- 
> 2.31.1

Otherwise LGTM.

	Jakub
  

* Jakub Jelinek:

>> +/* Fallback declaration for old glibc headers.  DL_FIND_EH_FRAME_DBASE is used
>> +   as a proxy to determine if <dlfcn.h> declares _dl_find_eh_frame.  */
>> +#if defined __GLIBC__ && !defined DL_FIND_EH_FRAME_DBASE
>> +#if NEED_DBASE_MEMBER
>> +void *_dl_find_eh_frame (void *__pc, void **__dbase) __attribute__ ((weak));
>> +#else
>> +void *_dl_find_eh_frame (void *__pc) __attribute__ ((weak));
>> +#endif
>> +#define USE_DL_FIND_EH_FRAME 1
>> +#define DL_FIND_EH_FRAME_CONDITION (_dl_find_eh_frame != NULL)
>> +#endif
>
> I'd prefer not to do this.  If we find glibc with the support in the
> headers, let's use it, otherwise let's keep using what we were doing before.

I've included a simplified version below, based on the _dl_find_object
patch for glibc.

This is a bit difficult to test, but I ran a full toolchain bootstrap
with GCC + glibc on all glibc-supported architectures (except Hurd and
one m68k variant; they do not presnetly build, see Joseph's testers).

I also tested this by copying the respective GCC-built libgcc_s into a
glibc build tree for run-time testing on i686-linux-gnu and
x86_64-linux-gnu.  There weren't any issues.  There are a buch of
unwinder tests in glibc, giving at least some coverage.

Thanks,
Florian

Subject: libgcc: Use _dl_find_object in _Unwind_Find_FDE

libgcc/ChangeLog:

	* unwind-dw2-fde-dip.c (_Unwind_Find_FDE): Call _dl_find_object
	if available.

---
 libgcc/unwind-dw2-fde-dip.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/libgcc/unwind-dw2-fde-dip.c b/libgcc/unwind-dw2-fde-dip.c
index fbb0fbdebb9..b837d8e4904 100644
--- a/libgcc/unwind-dw2-fde-dip.c
+++ b/libgcc/unwind-dw2-fde-dip.c
@@ -504,6 +504,24 @@ _Unwind_Find_FDE (void *pc, struct dwarf_eh_bases *bases)
   if (ret != NULL)
     return ret;
 
+  /* Use DLFO_STRUCT_HAS_EH_DBASE as a proxy for the existence of a glibc-style
+     _dl_find_object function.  */
+#ifdef DLFO_STRUCT_HAS_EH_DBASE
+  {
+    struct dl_find_object dlfo;
+    if (_dl_find_object (pc, &dlfo) == 0)
+      return find_fde_tail ((_Unwind_Ptr) pc, dlfo.dlfo_eh_frame,
+# if DLFO_STRUCT_HAS_EH_DBASE
+			    (_Unwind_Ptr) dlfo.dlfo_eh_dbase,
+# else
+			    NULL,
+# endif
+			    bases);
+    else
+      return NULL;
+    }
+#endif /* DLFO_STRUCT_HAS_EH_DBASE */
+
   data.pc = (_Unwind_Ptr) pc;
 #if NEED_DBASE_MEMBER
   data.dbase = NULL;
  

On Thu, Nov 25, 2021 at 09:42:53PM +0100, Florian Weimer wrote:
> I've included a simplified version below, based on the _dl_find_object
> patch for glibc.
> 
> This is a bit difficult to test, but I ran a full toolchain bootstrap
> with GCC + glibc on all glibc-supported architectures (except Hurd and
> one m68k variant; they do not presnetly build, see Joseph's testers).
> 
> I also tested this by copying the respective GCC-built libgcc_s into a
> glibc build tree for run-time testing on i686-linux-gnu and
> x86_64-linux-gnu.  There weren't any issues.  There are a buch of
> unwinder tests in glibc, giving at least some coverage.

See the comment I've just sent on this patch.
If the DLFO_STRUCT_HAS_EH_DBASE and DLFO_STRUCT_HAS_EH_COUNT
macros are gone, we'd need to use __GLIBC_PREREQ or configure test
or combination of the two.

Otherwise LGTM.

> Subject: libgcc: Use _dl_find_object in _Unwind_Find_FDE
> 
> libgcc/ChangeLog:
> 
> 	* unwind-dw2-fde-dip.c (_Unwind_Find_FDE): Call _dl_find_object
> 	if available.

	Jakub