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, 2 insertions, 0 deletions

diff --git a/include/dlfcn.h b/include/dlfcn.h
index e73294b0af..ae25f05303 100644
--- a/include/dlfcn.h
+++ b/include/dlfcn.h
@@ -4,6 +4,8 @@
 #include <link.h>		/* For ElfW.  */
 #include <stdbool.h>
 
+rtld_hidden_proto (_dl_find_object)
+
 /* Internally used flag.  */
 #define __RTLD_DLOPEN	0x80000000
 #define __RTLD_SPROF	0x40000000