https://github.com/kraj updated https://github.com/llvm/llvm-project/pull/138077
>From e9870d6a848a95cf58f890a7e6d3a93a27e7c061 Mon Sep 17 00:00:00 2001
From: Khem Raj <raj.k...@gmail.com>
Date: Wed, 30 Apr 2025 19:51:19 -0700
Subject: [PATCH] libunwind: Do not use __attribute__((target("gcs"))) with
non-clang compilers unwindlib: Use +gcs instead of gcs target attribute
GCC-15 has added gcs intrinsics [1] but the syntax for enabling it is
slightly different. This syntax works with clang too.
With gcc15 compiler libunwind's check for this macros is succeeding and it
ends up enabling 'gcs' by using function attribute, this works with clang
but not with gcc but '+gcs' works with both
We can see this in rust compiler bootstrap for aarch64/musl when system
uses gcc15, it ends up with these errors
Building libunwind.a for aarch64-poky-linux-musl
cargo:warning=/mnt/b/yoe/master/sources/poky/build/tmp/work/cortexa57-poky-linux-musl/rust/1.85.1/rustc-1.85.1-src/src/llvm-project/libunwind/src/UnwindLevel1.c:191:1:
error: arch extension 'gcs' should be prefixed by '+'
cargo:warning= 191 | unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor,
_Unwind_Exception *exception_object) {
cargo:warning= | ^~~~~~~~~~~~~
cargo:warning=/mnt/b/yoe/master/sources/poky/build/tmp/work/cortexa57-poky-linux-musl/rust/1.85.1/rustc-1.85.1-src/src/llvm-project/libunwind/src/UnwindLevel1.c:337:22:
error: arch extension 'gcs' should be prefixed by '+'
cargo:warning= 337 | _Unwind_Stop_Fn stop, void
*stop_parameter) {
cargo:warning= | ^~~~~~~~~~~~~~~
[1] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=5a6af707f0af
Signed-off-by: Khem Raj <raj.k...@gmail.com>
---
libunwind/src/UnwindLevel1.c | 4 ++--
libunwind/src/shadow_stack_unwind.h | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/libunwind/src/UnwindLevel1.c b/libunwind/src/UnwindLevel1.c
index a258a832a9c31..ccc36fab1ee88 100644
--- a/libunwind/src/UnwindLevel1.c
+++ b/libunwind/src/UnwindLevel1.c
@@ -188,7 +188,7 @@ extern int __unw_step_stage2(unw_cursor_t *);
#if defined(_LIBUNWIND_USE_GCS)
// Enable the GCS target feature to permit gcspop instructions to be used.
-__attribute__((target("gcs")))
+__attribute__((target("+gcs")))
#endif
static _Unwind_Reason_Code
unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception
*exception_object) {
@@ -332,7 +332,7 @@ unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor,
_Unwind_Exception *except
#if defined(_LIBUNWIND_USE_GCS)
// Enable the GCS target feature to permit gcspop instructions to be used.
-__attribute__((target("gcs")))
+__attribute__((target("+gcs")))
#endif
static _Unwind_Reason_Code
unwind_phase2_forced(unw_context_t *uc, unw_cursor_t *cursor,
diff --git a/libunwind/src/shadow_stack_unwind.h
b/libunwind/src/shadow_stack_unwind.h
index 1f229d8317116..ece49d028e5db 100644
--- a/libunwind/src/shadow_stack_unwind.h
+++ b/libunwind/src/shadow_stack_unwind.h
@@ -42,7 +42,7 @@
#include <arm_acle.h>
// We can only use GCS if arm_acle.h defines the GCS intrinsics.
-#ifdef _CHKFEAT_GCS
+#if defined(_CHKFEAT_GCS)
#define _LIBUNWIND_USE_GCS 1
#endif
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