[PATCH 4/4] libgcc: Use _dl_find_eh_frame in _Unwind_Find_FDE

[Florian Weimer]

* 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;