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Disable -fsplit-stack support on non-glibc targets

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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 with musl libc. 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 itself by
gcc-go (if available). On musl-based systems with split-stack support
(i.e. 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 gcc targets a glibc-based system. This check has been
added for x86 and s390x, the rs6000 config already checks for
TARGET_GLIBC_MAJOR. Other architectures do not have split-stack
support. With this patch applied, the gcc-go configure script will
detect that -fsplit-stack support is not available and will not use it.

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

This patch was written under the assumption that glibc is the only libc
implementation which supports the required fields at the required
offsets in the pthread_t TCB. The patch has been tested on Alpine Linux
Edge on the s390x and x86 architectures by bootstrapping Google's Go
implementation with gcc-go.

Signed-off-by: Sören Tempel <soeren@soeren-tempel.net>

gcc/ChangeLog:

	* common/config/s390/s390-common.cc (s390_supports_split_stack):
	Only support split-stack on glibc targets.
	* config/i386/gnu-user-common.h (STACK_CHECK_STATIC_BUILTIN): Ditto.
	* config/i386/gnu.h (defined): Ditto.
This commit is contained in:
Sören Tempel 2022-01-21 19:22:46 +00:00 committed by Richard Sandiford
parent afe91e2566
commit c163647ffb
3 changed files with 17 additions and 7 deletions
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14
gcc/common/config/s390/s390-common.cc
View File

@ -116,13 +116,19 @@ 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)
s390_supports_split_stack (bool report,
struct gcc_options *opts)
{
return true;
if (opts->x_linux_libc == LIBC_GLIBC)
return true;
if (report)
error ("%<-fsplit-stack%> currently only supported on GNU/Linux");
return false;
}
#undef TARGET_DEFAULT_TARGET_FLAGS

5
gcc/config/i386/gnu-user-common.h
View File

@ -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
targets glibc. */
#if HAVE_GAS_CFI_PERSONALITY_DIRECTIVE && OPTION_GLIBC
#define TARGET_CAN_SPLIT_STACK
#endif

5
gcc/config/i386/gnu.h
View File

@ -35,7 +35,10 @@ 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 implementations to avoid silent TCB corruptions. */
#if defined (TARGET_LIBC_PROVIDES_SSP) && OPTION_GLIBC
/* i386 glibc provides __stack_chk_guard in %gs:0x14. */
#define TARGET_THREAD_SSP_OFFSET 0x14