[libunwind] [libunwind] Pass -Wl,--export-dynamic on all supported platforms (PR #67205)

[Alexander Richardson via cfe-commits]

https://github.com/arichardson created https://github.com/llvm/llvm-project/pull/67205

I was trying to run the tests on FreeBSD and noticed that we weren't printing symbol names. It turns out this is because of the missing -Wl,--export dynamic flag. Instead of hardcoding the name of the flag and only passing it for Linux hosts, use a pre-existing CMake variable instead. I was not aware of this flag, but it appears to have been supported for the past 16 years (with support for more platforms added later): https://gitlab.kitware.com/cmake/cmake/-/commit/66d1930f5674f08e09f455b3f0777f2de3e0717e

>From 6f459b7cf539c17192e765578ac9f938e4f3af3f Mon Sep 17 00:00:00 2001
From: Alex Richardson <alexrichardson at google.com>
Date: Fri, 22 Sep 2023 16:11:49 -0700
Subject: [PATCH] [libunwind] Pass -Wl,--export-dynamic on all supported
 platforms

I was trying to run the tests on FreeBSD and noticed that we weren't
printing symbol names. It turns out this is because of the missing
-Wl,--export dynamic flag. Instead of hardcoding the name of the flag
and only passing it for Linux hosts, use a pre-existing CMake variable
instead. I was not aware of this flag, but it appears to have been
supported for the past 16 years (with support for more platforms added
later): https://gitlab.kitware.com/cmake/cmake/-/commit/66d1930f5674f08e09f455b3f0777f2de3e0717e
---
 libunwind/test/configs/llvm-libunwind-merged.cfg.in | 6 ++++--
 libunwind/test/configs/llvm-libunwind-shared.cfg.in | 6 ++++--
 libunwind/test/configs/llvm-libunwind-static.cfg.in | 6 ++++--
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/libunwind/test/configs/llvm-libunwind-merged.cfg.in b/libunwind/test/configs/llvm-libunwind-merged.cfg.in
index 10650f7edf66a2f..e6fafd1edd9756f 100644
--- a/libunwind/test/configs/llvm-libunwind-merged.cfg.in
+++ b/libunwind/test/configs/llvm-libunwind-merged.cfg.in
@@ -11,8 +11,10 @@ link_flags = []
 if @LIBUNWIND_ENABLE_CET@:
     compile_flags.append('-fcf-protection=full')
 
-if '@CMAKE_SYSTEM_NAME@' == 'Linux':
-    link_flags.append('-Wl,--export-dynamic')
+# Add -Wl,--export-dynamic if supported by the linker (this CMake variable will
+# be empty for Apple platforms).
+if len('@CMAKE_EXE_EXPORTS_CXX_FLAG@'):
+    link_flags.append('@CMAKE_EXE_EXPORTS_CXX_FLAG@')
 
 if '@CMAKE_DL_LIBS@':
     link_flags.append('-l at CMAKE_DL_LIBS@')
diff --git a/libunwind/test/configs/llvm-libunwind-shared.cfg.in b/libunwind/test/configs/llvm-libunwind-shared.cfg.in
index 97185e57234ff7f..f2e98c7a388dd32 100644
--- a/libunwind/test/configs/llvm-libunwind-shared.cfg.in
+++ b/libunwind/test/configs/llvm-libunwind-shared.cfg.in
@@ -10,8 +10,10 @@ link_flags = []
 if @LIBUNWIND_ENABLE_CET@:
     compile_flags.append('-fcf-protection=full')
 
-if '@CMAKE_SYSTEM_NAME@' == 'Linux':
-    link_flags.append('-Wl,--export-dynamic')
+# Add -Wl,--export-dynamic if supported by the linker (this CMake variable will
+# be empty for Apple platforms).
+if len('@CMAKE_EXE_EXPORTS_CXX_FLAG@'):
+    link_flags.append('@CMAKE_EXE_EXPORTS_CXX_FLAG@')
 
 if '@CMAKE_DL_LIBS@':
     link_flags.append('-l at CMAKE_DL_LIBS@')
diff --git a/libunwind/test/configs/llvm-libunwind-static.cfg.in b/libunwind/test/configs/llvm-libunwind-static.cfg.in
index fc6a18d057f3884..1fbdec249855d4a 100644
--- a/libunwind/test/configs/llvm-libunwind-static.cfg.in
+++ b/libunwind/test/configs/llvm-libunwind-static.cfg.in
@@ -13,8 +13,10 @@ if @LIBUNWIND_ENABLE_THREADS@:
 if @LIBUNWIND_ENABLE_CET@:
     compile_flags.append('-fcf-protection=full')
 
-if '@CMAKE_SYSTEM_NAME@' == 'Linux':
-    link_flags.append('-Wl,--export-dynamic')
+# Add -Wl,--export-dynamic if supported by the linker (this CMake variable will
+# be empty for Apple platforms).
+if len('@CMAKE_EXE_EXPORTS_CXX_FLAG@'):
+    link_flags.append('@CMAKE_EXE_EXPORTS_CXX_FLAG@')
 
 if '@CMAKE_DL_LIBS@':
     link_flags.append('-l at CMAKE_DL_LIBS@')