From c86b726c048eddc1be320c0bf64a897658bee13d Mon Sep 17 00:00:00 2001
From: Uros Bizjak <ubizjak@gmail.com>
Date: Wed, 18 May 2022 20:03:26 +0200
Subject: [PATCH] x86: Fix -fsplit-stack feature detection via 
 TARGET_CAN_SPLIT_STACK
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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.
---
 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.  */
