Cleanup linker unwinder integration
The linker shouldn't throw exceptions, but because it links with
libc++_static.a, there are code paths that could throw an exception. On
those code paths, the unwinder needs to lookup EH information for the
linker binary, and the linker had two inconsistent ways of doing this:
* dl_iterate_phdr (for libgcc): dlfcn.cpp defined a linker-internal
version of this API that forwarded to __loader_dl_iterate_phdr
* __gnu_Unwind_Find_exidx (for arm32 libgcc): linker_exidx_static.c was
an old, broken copy of exidx_static.c that used
__exidx_start/__exidx_end symbols. (The file should have used the
addresses of the symbols rather than their contents.)
The linker's data structures might be in an inconsistent state at a point
where exceptions are thrown, so it seems better to limit its unwinder to
just the linker binary's EH info. Rather than forward the dl* EH APIs,
link in the static-binary versions from libc_unwind_static.a. That library
is already part of libc_nomalloc.a, but include it directly with
whole_static_libs so that __gnu_Unwind_Find_exidx is defined when we're
using libgcc on arm32.
Try to link in libunwind_llvm.a into the arm32 linker binary so we're
using the same unwinder as normal arm32 binaries. I'm not sure the library
will appear in the right order, but maybe it doesn't matter given LLD's
unconventional archive linking semantics.
Test: bionic unit tests
Test: "readelf --dyn-syms linker" reports no UNDEF symbols
Test: "readelf -r linker" reports only relative relocations
Bug: none
Change-Id: I5982ec830ba0f15d066536de24f6cd7e9503498b
Merged-In: I5982ec830ba0f15d066536de24f6cd7e9503498b
diff --git a/linker/Android.bp b/linker/Android.bp
index 18f2527..bb9d26d 100644
--- a/linker/Android.bp
+++ b/linker/Android.bp
@@ -96,7 +96,6 @@
name: "linker_sources_arm",
srcs: [
"arch/arm/begin.S",
- "linker_exidx_static.c",
],
}
@@ -233,6 +232,7 @@
arm: {
srcs: [ ":linker_sources_arm" ],
version_script: ":linker_version_script_arm",
+ static_libs: ["libunwind_llvm"],
},
arm64: {
srcs: [":linker_sources_arm64"],
@@ -276,6 +276,17 @@
"liblinker_malloc",
],
+ // Ensure that if the linker needs __gnu_Unwind_Find_exidx, then the linker will have a
+ // definition of the symbol. The linker links against libgcc.a, whose arm32 unwinder has a weak
+ // reference to __gnu_Unwind_Find_exidx, which isn't sufficient to pull in the strong definition
+ // of __gnu_Unwind_Find_exidx from libc. An unresolved weak reference would create a
+ // non-relative dynamic relocation in the linker binary, which complicates linker startup.
+ //
+ // This line should be unnecessary because the linker's dependency on libunwind_llvm.a should
+ // override libgcc.a, but this line provides a simpler guarantee. It can be removed once the
+ // linker stops linking against libgcc.a's arm32 unwinder.
+ whole_static_libs: ["libc_unwind_static"],
+
name: "linker",
symlinks: ["linker_asan"],
recovery_available: true,
diff --git a/linker/dlfcn.cpp b/linker/dlfcn.cpp
index 18301e0..228e30a 100644
--- a/linker/dlfcn.cpp
+++ b/linker/dlfcn.cpp
@@ -31,6 +31,7 @@
#include "linker_globals.h"
#include "linker_dlwarning.h"
+#include <link.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
@@ -193,11 +194,6 @@
return do_dl_iterate_phdr(cb, data);
}
-// This function is needed by libgcc.a
-int dl_iterate_phdr(int (*cb)(dl_phdr_info* info, size_t size, void* data), void* data) {
- return __loader_dl_iterate_phdr(cb, data);
-}
-
#if defined(__arm__)
_Unwind_Ptr __loader_dl_unwind_find_exidx(_Unwind_Ptr pc, int* pcount) {
ScopedPthreadMutexLocker locker(&g_dl_mutex);
diff --git a/linker/linker_exidx_static.c b/linker/linker_exidx_static.c
deleted file mode 100644
index b38ef17..0000000
--- a/linker/linker_exidx_static.c
+++ /dev/null
@@ -1,46 +0,0 @@
-/*
- * Copyright (C) 2008 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * * Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in
- * the documentation and/or other materials provided with the
- * distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <link.h>
-
-/* Find the .ARM.exidx section (which in the case of a static executable
- * can be identified through its start and end symbols), and return its
- * beginning and numbe of entries to the caller. Note that for static
- * executables we do not need to use the value of the PC to find the
- * EXIDX section.
- */
-
-extern unsigned __exidx_end;
-extern unsigned __exidx_start;
-
-_Unwind_Ptr __gnu_Unwind_Find_exidx(_Unwind_Ptr pc __unused,
- int* pcount)
-{
- *pcount = (__exidx_end-__exidx_start)/8;
- return __exidx_start;
-}