[gcc r13-625] x86: Fix -fsplit-stack feature detection via TARGET_CAN_SPLIT_STACK

[gcc r13-625] x86: Fix -fsplit-stack feature detection via TARGET_CAN_SPLIT_STACK

[Uros Bizjak]

https://gcc.gnu.org/g:c86b726c048eddc1be320c0bf64a897658bee13d

commit r13-625-gc86b726c048eddc1be320c0bf64a897658bee13d
Author: Uros Bizjak <ubizjak@gmail.com>
Date:   Wed May 18 20:03:26 2022 +0200

    x86: Fix -fsplit-stack feature detection via  TARGET_CAN_SPLIT_STACK
    
    Since commit c163647ffbc9a20c8feb6e079dbecccfe016c82e -fsplit-stack
    is only supported on glibc targets. However, this original commit
    required some fixups. As part of the fixup, the changes to the
    gnu-user-common.h and gnu.h were partially reverted in commit
    60953a23d57b13a672f751bec0c6eefc059eb1ab thus causing TARGET_CAN_SPLIT_STACK
    to be defined for non-glibc targets even though -fsplit-stack is
    actually not supported and attempting to use it causes a runtime error.
    
    This causes gcc internal code, such as ./gcc/go/gospec.c to not
    correctly detect that -fsplit-stack is not supported and thus causes
    gccgo to fail compilation on non-glibc targets.
    
    This commit ensures that TARGET_CAN_SPLIT_STACK is only set if the
    default libc is glibc. It is presently unclear to me if there is a
    better way to detect glibc at pre-processor time.
    
    The proposed changes have been tested on x86 and x86_64 Alpine Linux
    (which uses musl libc) and fix compilation of gccgo for this target.
    
    Signed-off-by: Sören Tempel <soeren@soeren-tempel.net>
    
    gcc/ChangeLog:
    
            * config/i386/gnu-user-common.h (defined): Only define
            TARGET_CAN_SPLIT_STACK for glibc targets.
            * config/i386/gnu.h (defined): Ditto.

Diff:
---
 gcc/config/i386/gnu-user-common.h | 5 +++--
 gcc/config/i386/gnu.h             | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/gcc/config/i386/gnu-user-common.h b/gcc/config/i386/gnu-user-common.h
index 23b54c5be52..cab9be2bfb7 100644
--- a/gcc/config/i386/gnu-user-common.h
+++ b/gcc/config/i386/gnu-user-common.h
@@ -66,7 +66,8 @@ along with GCC; see the file COPYING3.  If not see
 #define STACK_CHECK_STATIC_BUILTIN 1
 
 /* We only build the -fsplit-stack support in libgcc if the
-   assembler has full support for the CFI directives.  */
-#if HAVE_GAS_CFI_PERSONALITY_DIRECTIVE
+   assembler has full support for the CFI directives.  Also
+   we only support -fsplit-stack on glibc targets.  */
+#if (DEFAULT_LIBC == LIBC_GLIBC) && HAVE_GAS_CFI_PERSONALITY_DIRECTIVE
 #define TARGET_CAN_SPLIT_STACK
 #endif
diff --git a/gcc/config/i386/gnu.h b/gcc/config/i386/gnu.h
index 401e60c9a02..fb8d69a97d8 100644
--- a/gcc/config/i386/gnu.h
+++ b/gcc/config/i386/gnu.h
@@ -41,8 +41,9 @@ along with GCC.  If not, see <http://www.gnu.org/licenses/>.
 #define TARGET_THREAD_SSP_OFFSET        0x14
 
 /* We only build the -fsplit-stack support in libgcc if the
-   assembler has full support for the CFI directives.  */
-#if HAVE_GAS_CFI_PERSONALITY_DIRECTIVE
+   assembler has full support for the CFI directives.  Also
+   we only support -fsplit-stack on glibc targets.  */
+#if (DEFAULT_LIBC == LIBC_GLIBC) && HAVE_GAS_CFI_PERSONALITY_DIRECTIVE
 #define TARGET_CAN_SPLIT_STACK
 #endif
 /* We steal the last transactional memory word.  */