[libunwind] Try to add --unwindlib=none while configuring and building libunwind
If Clang is set up to link directly against libunwind (via the
--unwindlib option, or the corresponding builtin default option),
configuring libunwind will fail while bootstrapping (before the
initial libunwind is built), because every cmake test will
fail due to -lunwind not being found, and linking the shared library
will fail similarly.
Check if --unwindlib=none is supported, and add it in that case.
Using check_c_compiler_flag on its own doesn't work, because that only
adds the tested flag to the compilation command, and if -lunwind is
missing, the linking step would still fail - instead try adding it
to CMAKE_REQUIRED_FLAGS and restore the variable if it doesn't work.
This avoids having to pass --unwindlib=none while building libunwind.
Differential Revision: https://reviews.llvm.org/D112126
GitOrigin-RevId: 7af584ed87cc6eddb6adbc451c90fb8867469e06
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f16d49a..bec0d1f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,7 +23,11 @@
"Specify path to libc++ source.")
if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR OR LIBUNWIND_STANDALONE_BUILD)
- project(libunwind LANGUAGES C CXX ASM)
+ # We may have an incomplete toolchain - do language support tests without
+ # linking.
+ include(EnableLanguageNolink)
+ project(libunwind LANGUAGES NONE)
+ llvm_enable_language_nolink(C CXX ASM)
set(PACKAGE_NAME libunwind)
set(PACKAGE_VERSION 14.0.0git)
@@ -179,6 +183,14 @@
# Get required flags.
add_target_flags_if(LIBUNWIND_BUILD_32_BITS "-m32")
+# Compiler tests may be failing if the compiler implicitly links in libunwind,
+# which doesn't exist yet. This gets waived by --unwindlib=none
+# later in config-ix below, but the tests for --target etc before that may
+# be failing due to it. Only test compilation, not linking, for these
+# tests here now.
+set(CMAKE_TRY_COMPILE_TARGET_TYPE_ORIG ${CMAKE_TRY_COMPILE_TARGET_TYPE})
+set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+
if(LIBUNWIND_TARGET_TRIPLE)
add_target_flags_if_supported("--target=${LIBUNWIND_TARGET_TRIPLE}")
endif()
@@ -188,6 +200,7 @@
if(LIBUNWIND_SYSROOT)
add_target_flags_if_supported("--sysroot=${LIBUNWIND_SYSROOT}")
endif()
+set(CMAKE_TRY_COMPILE_TARGET_TYPE ${CMAKE_TRY_COMPILE_TARGET_TYPE_ORIG})
# Configure compiler.
include(config-ix)
diff --git a/cmake/config-ix.cmake b/cmake/config-ix.cmake
index 78f116c..ec10733 100644
--- a/cmake/config-ix.cmake
+++ b/cmake/config-ix.cmake
@@ -2,9 +2,18 @@
include(CheckCCompilerFlag)
include(CheckCXXCompilerFlag)
include(CheckLibraryExists)
+include(CheckLinkerFlag)
include(CheckSymbolExists)
include(CheckCSourceCompiles)
+# The compiler driver may be implicitly trying to link against libunwind, which
+# might not work if libunwind doesn't exist yet. Try to check if
+# --unwindlib=none is supported, and use that if possible.
+llvm_check_linker_flag("--unwindlib=none" LIBUNWIND_SUPPORTS_UNWINDLIB_NONE_FLAG)
+if (LIBUNWIND_SUPPORTS_UNWINDLIB_NONE_FLAG)
+ set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} --unwindlib=none")
+endif()
+
check_library_exists(c fopen "" LIBUNWIND_HAS_C_LIB)
if (NOT LIBUNWIND_USE_COMPILER_RT)
@@ -25,11 +34,11 @@
# required for the link to go through. We remove sanitizers from the
# configuration checks to avoid spurious link errors.
-check_c_compiler_flag(-nostdlib++ LIBUNWIND_SUPPORTS_NOSTDLIBXX_FLAG)
+llvm_check_linker_flag(-nostdlib++ LIBUNWIND_SUPPORTS_NOSTDLIBXX_FLAG)
if (LIBUNWIND_SUPPORTS_NOSTDLIBXX_FLAG)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdlib++")
else()
- check_c_compiler_flag(-nodefaultlibs LIBUNWIND_SUPPORTS_NODEFAULTLIBS_FLAG)
+ llvm_check_linker_flag(-nodefaultlibs LIBUNWIND_SUPPORTS_NODEFAULTLIBS_FLAG)
if (LIBUNWIND_SUPPORTS_NODEFAULTLIBS_FLAG)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nodefaultlibs")
endif()
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index ce3217f..3b20e97 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -83,6 +83,7 @@
endif()
# Setup flags.
+add_link_flags_if(LIBUNWIND_SUPPORTS_UNWINDLIB_NONE_FLAG --unwindlib=none)
if (LIBUNWIND_SUPPORTS_NOSTDLIBXX_FLAG)
add_link_flags_if_supported(-nostdlib++)
else()
