elf: Add _dl_find_object function

It can be used to speed up the libgcc unwinder, and the internal
_dl_find_dso_for_object function (which is used for caller
identification in dlopen and related functions, and in dladdr).

_dl_find_object is in the internal namespace due to bug 28503.
If libgcc switches to _dl_find_object, this namespace issue will
be fixed.  It is located in libc for two reasons: it is necessary
to forward the call to the static libc after static dlopen, and
there is a link ordering issue with -static-libgcc and libgcc_eh.a
because libc.so is not a linker script that includes ld.so in the
glibc build tree (so that GCC's internal -lc after libgcc_eh.a does
not pick up ld.so).

It is necessary to do the i386 customization in the
sysdeps/x86/bits/dl_find_object.h header shared with x86-64 because
otherwise, multilib installations are broken.

The implementation uses software transactional memory, as suggested
by Torvald Riegel.  Two copies of the supporting data structures are
used, also achieving full async-signal-safety.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/elf/Versions b/elf/Versions
index bfe1aec293..a4f1e76708 100644
--- a/elf/Versions
+++ b/elf/Versions
@@ -20,6 +20,9 @@ libc {
     __register_frame_info_table_bases; _Unwind_Find_FDE;
   }
 %endif
+  GLIBC_2.35 {
+    _dl_find_object;
+  }
   GLIBC_PRIVATE {
     # functions used in other libraries
     __libc_early_init;