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, 14 insertions, 0 deletions

diff --git a/include/atomic_wide_counter.h b/include/atomic_wide_counter.h
index 31f009d5e6..d1c40cd85f 100644
--- a/include/atomic_wide_counter.h
+++ b/include/atomic_wide_counter.h
@@ -31,6 +31,12 @@ __atomic_wide_counter_load_relaxed (__atomic_wide_counter *c)
 }
 
 static inline uint64_t
+__atomic_wide_counter_load_acquire (__atomic_wide_counter *c)
+{
+  return atomic_load_acquire (&c->__value64);
+}
+
+static inline uint64_t
 __atomic_wide_counter_fetch_add_relaxed (__atomic_wide_counter *c,
                                          unsigned int val)
 {
@@ -64,6 +70,14 @@ __atomic_wide_counter_fetch_xor_release (__atomic_wide_counter *c,
 uint64_t __atomic_wide_counter_load_relaxed (__atomic_wide_counter *c)
   attribute_hidden;
 
+static inline uint64_t
+__atomic_wide_counter_load_acquire (__atomic_wide_counter *c)
+{
+  uint64_t r = __atomic_wide_counter_load_relaxed (c);
+  atomic_thread_fence_acquire ();
+  return r;
+}
+
 uint64_t __atomic_wide_counter_fetch_add_relaxed (__atomic_wide_counter *c,
                                                   unsigned int op)
   attribute_hidden;