main/gcc: disable -fsplit-stack on non-glibc targets

The -fsplit-stack option requires specific fields at hardcoded offsets
in the pthread_t TCB, musl does not have these fields. Therefore,
enabling this compiler option on musl causes silent memory corruptions
in the pthread_t TCB. gcc-go enables this option by default if it is
available (x86 and s390x). This commit fixes bootstrapping of Google's
Go implementation with gcc-go on s390x (see !27944).

See https://www.openwall.com/lists/musl/2012/10/16/12

main/gcc/0042-Disable-fsplit-stack-support-on-non-glibc-targets.patch

+From 5b7b256eafc888a3be2dcee1e01f8dc6a814d1a6 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?S=C3=B6ren=20Tempel?= <soeren+git@soeren-tempel.net>
+Date: Wed, 15 Dec 2021 00:14:19 +0100
+Subject: [PATCH] Disable -fsplit-stack support on non-glibc targets
+
+The -fsplit-stack option requires the pthread_t TCB definition in the
+libc to provide certain struct fields at specific hardcoded offsets. As
+far as I know, only glibc provides these fields at the required offsets.
+Most notably, musl libc does not have these fields. However, since gcc
+accesses the fields using a fixed offset this does not cause a
+compile-time error but instead results in a silent memory corruption at
+run-time. For example, on s390x libgcc's __stack_split_initialize CTOR
+will overwrite the cancel field in the pthread_t TCB on musl.
+
+The -fsplit-stack option is used within the gcc code base by gcc-go by
+default. On musl based systems with split-stack support (e.g. s390x or
+x86) this causes Go programs compiled with gcc-go to misbehave at
+run-time.
+
+This patch fixes gcc-go on musl by disabling -fsplit-stack in gcc itself
+since it is not supported on non-glibc targets anyhow. This is achieved
+by checking if TARGET_GLIBC_MAJOR is defined to a non-zero value (it
+defaults to zero on non-glibc systems). The check has been added for x86
+and s390x, the rs6000 config already checks for TARGET_GLIBC_MAJOR. With
+this patch applied, the gcc-go configure script will detect that
+-fsplit-stack support is not available and will not use it.
+
+This patch has been tested on Alpine Linux Edge on the s390x
+architecture by bootstrapping Google's Go implementation with gcc-go.
+
+See https://www.openwall.com/lists/musl/2012/10/16/12
+---
+ gcc/common/config/s390/s390-common.c | 9 ++++++++-
+ gcc/config/i386/gnu-user-common.h    | 5 +++--
+ gcc/config/i386/gnu.h                | 6 +++++-
+ 3 files changed, 16 insertions(+), 4 deletions(-)
+
+diff --git a/gcc/common/config/s390/s390-common.c b/gcc/common/config/s390/s390-common.c
+index b6bc8501742..afbd8d3fe66 100644
+--- a/gcc/common/config/s390/s390-common.c
++++ b/gcc/common/config/s390/s390-common.c
+@@ -116,13 +116,20 @@ s390_handle_option (struct gcc_options *opts ATTRIBUTE_UNUSED,
+ 
+ /* -fsplit-stack uses a field in the TCB, available with glibc-2.23.
+    We don't verify it, since earlier versions just have padding at
+-   its place, which works just as well.  */
++   its place, which works just as well. For other libc implementations
++   we disable the feature entirely to avoid corrupting the TCB.  */
+ 
+ static bool
+ s390_supports_split_stack (bool report ATTRIBUTE_UNUSED,
+ 			   struct gcc_options *opts ATTRIBUTE_UNUSED)
+ {
++#if TARGET_GLIBC_MAJOR
+   return true;
++#else
++  if (report)
++    error("%<-fsplit-stack%> currently only supported on GNU/Linux");
++  return false;
++#endif
+ }
+ 
+ #undef TARGET_DEFAULT_TARGET_FLAGS
+diff --git a/gcc/config/i386/gnu-user-common.h b/gcc/config/i386/gnu-user-common.h
+index 00226f5a455..554e146dbbe 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 and
++   uses glibc.  */
++#if HAVE_GAS_CFI_PERSONALITY_DIRECTIVE && TARGET_GLIBC_MAJOR
+ #define TARGET_CAN_SPLIT_STACK
+ #endif
+diff --git a/gcc/config/i386/gnu.h b/gcc/config/i386/gnu.h
+index 25fbc07f58c..895a7369816 100644
+--- a/gcc/config/i386/gnu.h
++++ b/gcc/config/i386/gnu.h
+@@ -35,7 +35,11 @@ along with GCC.  If not, see <http://www.gnu.org/licenses/>.
+    crti.o%s %{static:crtbeginT.o%s;shared|pie:crtbeginS.o%s;:crtbegin.o%s}"
+ #endif
+ 
+-#ifdef TARGET_LIBC_PROVIDES_SSP
++/* -fsplit-stack uses a field in the TCB at a fixed offset. This
++   field is only available for glibc. Disable -fsplit-stack for
++   other libc implementation to avoid silent TCB corruptions.  */
++
++#if defined (TARGET_LIBC_PROVIDES_SSP) && TARGET_GLIBC_MAJOR
+ 
+ /* i386 glibc provides __stack_chk_guard in %gs:0x14.  */
+ #define TARGET_THREAD_SSP_OFFSET        0x14

main/gcc/APKBUILD

@@ -8,7 +8,7 @@ pkgver=11.2.1_git20211128
 [ "$CHOST" != "$CTARGET" ] && _target="-$CTARGET_ARCH" || _target=""
 
 pkgname="$pkgname$_target"
-pkgrel=2
+pkgrel=3
 pkgdesc="The GNU Compiler Collection"
 url="https://gcc.gnu.org"
 arch="all"
@@ -220,6 +220,7 @@ source="https://dev.alpinelinux.org/~nenolod/gcc-${pkgver}.tar.xz
 	0039-Fix-attempt-to-use-poisoned-calloc-error-in-libgccji.patch
 	0040-stddef.h-add-support-for-musl-typedef-macro-guards.patch
 	0041-gcc-go-Use-int64-type-as-offset-argument-for-mmap.patch
+	0042-Disable-fsplit-stack-support-on-non-glibc-targets.patch
 	"
 
 # we build out-of-tree
@@ -726,4 +727,5 @@ ca185b3e0644dab6a87bf524042c72069ffda0cde578e803bd59a9c5e40ba4d7d6f0be49836bc3aa
 2c5edf9e3fe6822a322c1dc75218062afb56799c304aa583c4e1e80136c6262cbd9bb950843f167b40639c6623a33a0475990c4452e03307af434dc8760d437d  0039-Fix-attempt-to-use-poisoned-calloc-error-in-libgccji.patch
 8e44678fc77094a2c0cbc78575759ee51d50ea53189cf4d651c8501eb1b46210bb6d5969b81f5f63532914320971e7a1e2e80b32cb679ab41af86f21742b4c19  0040-stddef.h-add-support-for-musl-typedef-macro-guards.patch
 e4d2466191b4acde115917506c285b617d6210bf3603e705ca3d905e4e28b12e399b16898f6ab9996b1d4fbfa3aed554e86931ed7f13fc13a9459af7f29f4393  0041-gcc-go-Use-int64-type-as-offset-argument-for-mmap.patch
+5e04b9a6d39b708daedcef494e4aed59b1a97d2052ed7eb8d1e3da5faa70dc5e1fa3ee249c685e820109d5605ee2b66154856b0ffccf7b8a49af1a1da9350ebf  0042-Disable-fsplit-stack-support-on-non-glibc-targets.patch
 "