95 lines
4.1 KiB
Diff
95 lines
4.1 KiB
Diff
From 5b7b256eafc888a3be2dcee1e01f8dc6a814d1a6 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?S=C3=B6ren=20Tempel?= <soeren+git@soeren-tempel.net>
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Date: Wed, 15 Dec 2021 00:14:19 +0100
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Subject: [PATCH] Disable -fsplit-stack support on non-glibc targets
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The -fsplit-stack option requires the pthread_t TCB definition in the
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libc to provide certain struct fields at specific hardcoded offsets. As
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far as I know, only glibc provides these fields at the required offsets.
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Most notably, musl libc does not have these fields. However, since gcc
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accesses the fields using a fixed offset this does not cause a
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compile-time error but instead results in a silent memory corruption at
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run-time. For example, on s390x libgcc's __stack_split_initialize CTOR
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will overwrite the cancel field in the pthread_t TCB on musl.
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The -fsplit-stack option is used within the gcc code base by gcc-go by
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default. On musl based systems with split-stack support (e.g. s390x or
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x86) this causes Go programs compiled with gcc-go to misbehave at
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run-time.
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This patch fixes gcc-go on musl by disabling -fsplit-stack in gcc itself
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since it is not supported on non-glibc targets anyhow. This is achieved
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by checking if TARGET_GLIBC_MAJOR is defined to a non-zero value (it
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defaults to zero on non-glibc systems). The check has been added for x86
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and s390x, the rs6000 config already checks for TARGET_GLIBC_MAJOR. With
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this patch applied, the gcc-go configure script will detect that
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-fsplit-stack support is not available and will not use it.
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This patch has been tested on Alpine Linux Edge on the s390x
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architecture by bootstrapping Google's Go implementation with gcc-go.
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See https://www.openwall.com/lists/musl/2012/10/16/12
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---
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gcc/common/config/s390/s390-common.c | 9 ++++++++-
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gcc/config/i386/gnu-user-common.h | 5 +++--
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gcc/config/i386/gnu.h | 6 +++++-
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3 files changed, 16 insertions(+), 4 deletions(-)
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diff --git a/gcc/common/config/s390/s390-common.c b/gcc/common/config/s390/s390-common.c
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index b6bc8501742..afbd8d3fe66 100644
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--- a/gcc/common/config/s390/s390-common.c
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+++ b/gcc/common/config/s390/s390-common.c
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@@ -116,13 +116,20 @@ s390_handle_option (struct gcc_options *opts ATTRIBUTE_UNUSED,
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/* -fsplit-stack uses a field in the TCB, available with glibc-2.23.
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We don't verify it, since earlier versions just have padding at
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- its place, which works just as well. */
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+ its place, which works just as well. For other libc implementations
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+ we disable the feature entirely to avoid corrupting the TCB. */
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static bool
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s390_supports_split_stack (bool report ATTRIBUTE_UNUSED,
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struct gcc_options *opts ATTRIBUTE_UNUSED)
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{
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+#if TARGET_GLIBC_MAJOR
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return true;
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+#else
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+ if (report)
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+ error("%<-fsplit-stack%> currently only supported on GNU/Linux");
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+ return false;
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+#endif
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}
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#undef TARGET_DEFAULT_TARGET_FLAGS
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diff --git a/gcc/config/i386/gnu-user-common.h b/gcc/config/i386/gnu-user-common.h
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index 00226f5a455..554e146dbbe 100644
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--- a/gcc/config/i386/gnu-user-common.h
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+++ b/gcc/config/i386/gnu-user-common.h
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@@ -66,7 +66,8 @@ along with GCC; see the file COPYING3. If not see
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#define STACK_CHECK_STATIC_BUILTIN 1
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/* We only build the -fsplit-stack support in libgcc if the
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- assembler has full support for the CFI directives. */
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-#if HAVE_GAS_CFI_PERSONALITY_DIRECTIVE
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+ assembler has full support for the CFI directives and
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+ uses glibc. */
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+#if HAVE_GAS_CFI_PERSONALITY_DIRECTIVE && TARGET_GLIBC_MAJOR
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#define TARGET_CAN_SPLIT_STACK
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#endif
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diff --git a/gcc/config/i386/gnu.h b/gcc/config/i386/gnu.h
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index 25fbc07f58c..895a7369816 100644
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--- a/gcc/config/i386/gnu.h
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+++ b/gcc/config/i386/gnu.h
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@@ -35,7 +35,11 @@ along with GCC. If not, see <http://www.gnu.org/licenses/>.
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crti.o%s %{static:crtbeginT.o%s;shared|pie:crtbeginS.o%s;:crtbegin.o%s}"
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#endif
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-#ifdef TARGET_LIBC_PROVIDES_SSP
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+/* -fsplit-stack uses a field in the TCB at a fixed offset. This
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+ field is only available for glibc. Disable -fsplit-stack for
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+ other libc implementation to avoid silent TCB corruptions. */
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+
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+#if defined (TARGET_LIBC_PROVIDES_SSP) && TARGET_GLIBC_MAJOR
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/* i386 glibc provides __stack_chk_guard in %gs:0x14. */
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#define TARGET_THREAD_SSP_OFFSET 0x14
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