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/dl-support.c b/elf/dl-support.c
index d2aa52d78a..a9d63ffe46 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -43,6 +43,7 @@
 #include <dl-vdso.h>
 #include <dl-vdso-setup.h>
 #include <dl-auxv.h>
+#include <dl-find_object.h>
 
 extern char *__progname;
 char **_dl_argv = &__progname;	/* This is checked for some error messages.  */
@@ -417,6 +418,8 @@ _dl_non_dynamic_init (void)
 	  break;
 	}
 
+  call_function_static_weak (_dl_find_object_init);
+
   /* Setup relro on the binary itself.  */
   if (_dl_main_map.l_relro_size != 0)
     _dl_protect_relro (&_dl_main_map);