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[libunwind] unw_* alias fixes for ELF and Mach-O
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Rename the CMake option, LIBUNWIND_HERMETIC_STATIC_LIBRARY, to
LIBUNWIND_HIDE_SYMBOLS. Rename the C macro define,
_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS, to _LIBUNWIND_HIDE_SYMBOLS,
because now the macro adds a .hidden directive rather than merely
suppress visibility annotations.

For ELF, when LIBUNWIND_HIDE_SYMBOLS is enabled, mark unw_getcontext as
hidden. This symbol is the only one defined using src/assembly.h's
WEAK_ALIAS macro. Other unw_* weak aliases are defined in C++ and are
already hidden.

Mach-O doesn't support weak aliases, so remove .weak_reference and
weak_import. When LIBUNWIND_HIDE_SYMBOLS is enabled, output
.private_extern for the unw_* aliases.

In assembly.h, add missing SYMBOL_NAME macro invocations, which are
used to prefix symbol names with '_' on some targets.

Fixes PR46709.

Reviewed By: #libunwind, phosek, compnerd, steven_wu

Differential Revision: https://reviews.llvm.org/D93003
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@rprichard
rprichard committed Feb 23, 2021
1 parent 0df59f2 commit 729899f
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Showing 6 changed files with 31 additions and 17 deletions.
2 changes: 1 addition & 1 deletion clang/cmake/caches/Fuchsia-stage2.cmake
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Expand Up @@ -179,7 +179,7 @@ if(FUCHSIA_SDK)
set(RUNTIMES_${target}-unknown-fuchsia_CMAKE_SYSROOT ${FUCHSIA_${target}_SYSROOT} CACHE PATH "")
set(RUNTIMES_${target}-unknown-fuchsia_COMPILER_RT_USE_BUILTINS_LIBRARY ON CACHE BOOL "")
set(RUNTIMES_${target}-unknown-fuchsia_LIBUNWIND_USE_COMPILER_RT ON CACHE BOOL "")
set(RUNTIMES_${target}-unknown-fuchsia_LIBUNWIND_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
set(RUNTIMES_${target}-unknown-fuchsia_LIBUNWIND_HIDE_SYMBOLS ON CACHE BOOL "")
set(RUNTIMES_${target}-unknown-fuchsia_LIBUNWIND_INSTALL_STATIC_LIBRARY OFF CACHE BOOL "")
set(RUNTIMES_${target}-unknown-fuchsia_LIBCXXABI_USE_COMPILER_RT ON CACHE BOOL "")
set(RUNTIMES_${target}-unknown-fuchsia_LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
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4 changes: 2 additions & 2 deletions libunwind/CMakeLists.txt
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Expand Up @@ -102,7 +102,7 @@ elseif(LIBUNWIND_BUILD_32_BITS)
message(FATAL_ERROR "LIBUNWIND_BUILD_32_BITS=ON is not supported on this platform.")
endif()

option(LIBUNWIND_HERMETIC_STATIC_LIBRARY
option(LIBUNWIND_HIDE_SYMBOLS
"Do not export any symbols from the static library." OFF)

#===============================================================================
Expand Down Expand Up @@ -321,7 +321,7 @@ endif()

# Disable DLL annotations on Windows for static builds.
if (WIN32 AND LIBUNWIND_ENABLE_STATIC AND NOT LIBUNWIND_ENABLE_SHARED)
add_definitions(-D_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS)
add_definitions(-D_LIBUNWIND_HIDE_SYMBOLS)
endif()

if (LIBUNWIND_HAS_COMMENT_LIB_PRAGMA)
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4 changes: 2 additions & 2 deletions libunwind/src/CMakeLists.txt
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Expand Up @@ -164,11 +164,11 @@ if (LIBUNWIND_ENABLE_STATIC)
LINKER_LANGUAGE C
OUTPUT_NAME "unwind")

if(LIBUNWIND_HERMETIC_STATIC_LIBRARY)
if(LIBUNWIND_HIDE_SYMBOLS)
append_flags_if_supported(UNWIND_STATIC_LIBRARY_FLAGS -fvisibility=hidden)
append_flags_if_supported(UNWIND_STATIC_LIBRARY_FLAGS -fvisibility-global-new-delete-hidden)
target_compile_options(unwind_static PRIVATE ${UNWIND_STATIC_LIBRARY_FLAGS})
target_compile_definitions(unwind_static PRIVATE _LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS)
target_compile_definitions(unwind_static PRIVATE _LIBUNWIND_HIDE_SYMBOLS)
endif()

list(APPEND LIBUNWIND_BUILD_TARGETS "unwind_static")
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25 changes: 17 additions & 8 deletions libunwind/src/assembly.h
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Expand Up @@ -70,12 +70,15 @@
#if defined(__APPLE__)

#define SYMBOL_IS_FUNC(name)
#define EXPORT_SYMBOL(name)
#define HIDDEN_SYMBOL(name) .private_extern name
#define WEAK_SYMBOL(name) .weak_reference name
#if defined(_LIBUNWIND_HIDE_SYMBOLS)
#define EXPORT_SYMBOL(name) HIDDEN_SYMBOL(name)
#else
#define EXPORT_SYMBOL(name)
#endif
#define WEAK_ALIAS(name, aliasname) \
.globl SYMBOL_NAME(aliasname) SEPARATOR \
WEAK_SYMBOL(aliasname) SEPARATOR \
EXPORT_SYMBOL(SYMBOL_NAME(aliasname)) SEPARATOR \
SYMBOL_NAME(aliasname) = SYMBOL_NAME(name)

#define NO_EXEC_STACK_DIRECTIVE
Expand All @@ -87,17 +90,23 @@
#else
#define SYMBOL_IS_FUNC(name) .type name,@function
#endif
#define EXPORT_SYMBOL(name)
#define HIDDEN_SYMBOL(name) .hidden name
#if defined(_LIBUNWIND_HIDE_SYMBOLS)
#define EXPORT_SYMBOL(name) HIDDEN_SYMBOL(name)
#else
#define EXPORT_SYMBOL(name)
#endif
#define WEAK_SYMBOL(name) .weak name

#if defined(__hexagon__)
#define WEAK_ALIAS(name, aliasname) \
WEAK_SYMBOL(aliasname) SEPARATOR \
#define WEAK_ALIAS(name, aliasname) \
EXPORT_SYMBOL(SYMBOL_NAME(aliasname)) SEPARATOR \
WEAK_SYMBOL(SYMBOL_NAME(aliasname)) SEPARATOR \
.equiv SYMBOL_NAME(aliasname), SYMBOL_NAME(name)
#else
#define WEAK_ALIAS(name, aliasname) \
WEAK_SYMBOL(aliasname) SEPARATOR \
EXPORT_SYMBOL(SYMBOL_NAME(aliasname)) SEPARATOR \
WEAK_SYMBOL(SYMBOL_NAME(aliasname)) SEPARATOR \
SYMBOL_NAME(aliasname) = SYMBOL_NAME(name)
#endif

Expand All @@ -119,7 +128,7 @@
.section .drectve,"yn" SEPARATOR \
.ascii "-export:", #name, "\0" SEPARATOR \
.text
#if defined(_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS)
#if defined(_LIBUNWIND_HIDE_SYMBOLS)
#define EXPORT_SYMBOL(name)
#else
#define EXPORT_SYMBOL(name) EXPORT_SYMBOL2(name)
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11 changes: 8 additions & 3 deletions libunwind/src/config.h
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Expand Up @@ -52,7 +52,8 @@
#endif
#endif

#if defined(_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS)
#if defined(_LIBUNWIND_HIDE_SYMBOLS)
// The CMake file passes -fvisibility=hidden to control ELF/Mach-O visibility.
#define _LIBUNWIND_EXPORT
#define _LIBUNWIND_HIDDEN
#else
Expand All @@ -70,11 +71,15 @@
#define SYMBOL_NAME(name) XSTR(__USER_LABEL_PREFIX__) #name

#if defined(__APPLE__)
#if defined(_LIBUNWIND_HIDE_SYMBOLS)
#define _LIBUNWIND_ALIAS_VISIBILITY(name) __asm__(".private_extern " name)
#else
#define _LIBUNWIND_ALIAS_VISIBILITY(name)
#endif
#define _LIBUNWIND_WEAK_ALIAS(name, aliasname) \
__asm__(".globl " SYMBOL_NAME(aliasname)); \
__asm__(SYMBOL_NAME(aliasname) " = " SYMBOL_NAME(name)); \
extern "C" _LIBUNWIND_EXPORT __typeof(name) aliasname \
__attribute__((weak_import));
_LIBUNWIND_ALIAS_VISIBILITY(SYMBOL_NAME(aliasname));
#elif defined(__ELF__)
#define _LIBUNWIND_WEAK_ALIAS(name, aliasname) \
extern "C" _LIBUNWIND_EXPORT __typeof(name) aliasname \
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2 changes: 1 addition & 1 deletion llvm/utils/gn/secondary/libunwind/src/BUILD.gn
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Expand Up @@ -111,7 +111,7 @@ if (libunwind_enable_static) {
if (!invoker.export) {
cflags = [ "-fvisibility=hidden" ]
cflags_cc = [ "-fvisibility-global-new-delete-hidden" ]
defines = [ "_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS" ]
defines = [ "_LIBUNWIND_HIDE_SYMBOLS" ]
}
deps = [ "//compiler-rt/lib/builtins" ]
configs += [ ":unwind_config" ]
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