Move dl_unwind_find_exidx from libdl.a to libc.a

arm32 has two special APIs to find exidx exception handling info,
dl_unwind_find_exidx and __gnu_Unwind_Find_exdix. The two functions have
identical behavior and function prototypes. libgcc's arm32 unwinder calls
__gnu_Unwind_Find_exdix, whereas LLVM's libunwind previously called
__gnu_Unwind_Find_exdix, but switched to dl_unwind_find_exidx as a result
of three patches (D30306, D30681, D39468).

In Bionic, for dynamic linking, __gnu_Unwind_Find_exdix in libc.so calls
dl_unwind_find_exidx in libdl.so.

For static executables, though, __gnu_Unwind_Find_exdix in libc.a used the
__exidx_* symbols, while dl_unwind_find_exidx in libdl.a(libdl_static.o)
was a return-0 no-op.

To fix the LLVM unwinder, replace the no-op dl_unwind_find_exidx in
libdl.a with a real function in libc.a(exidx_static.o), and have the GNU
function call the dl function for more consistency with dynamic linking.

dl_iterate_phdr follows a similar pattern, where the function exists in
libc.a and libdl.so (not libc.so or libdl.a).

This change makes unwinding work with an updated libunwind_llvm on arm32,
and it helps to allow unwinding in static executables without libdl.a.

Bug: https://github.com/android/ndk/issues/1094
Bug: http://b/141485154
Test: NDK tests, bionic unit tests
Change-Id: Ieeeb9b39a0e28544e21f9afe6fe51ef10d7c828c

1 files changed, 0 insertions, 6 deletions

diff --git a/libdl/libdl_static.cpp b/libdl/libdl_static.cpp
index 0a36e6f16..3bbf96329 100644
--- a/libdl/libdl_static.cpp
+++ b/libdl/libdl_static.cpp
@@ -41,9 +41,3 @@ int dladdr(const void* /*addr*/, Dl_info* /*info*/) {
 int dlclose(void* /*handle*/) {
   return -1;
 }
-
-#if defined(__arm__)
-_Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr /*pc*/, int* /*pcount*/) {
-  return 0;
-}
-#endif