On Sat, Dec 18, 2021 at 2:44 AM soeren--- via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > From: Sören Tempel <soeren+...@soeren-tempel.net> > > 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 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. > 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 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.c (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. > --- > 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 > }
I think it should check OPTION_MUSL at runtime instead of TARGET_GLIBC_MAJOR at compile time. or rather opts->x_linux_libc == LIBC_MUSL The others should be done similarly too. Thanks, Andrew > > #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..69f2d7415ad 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 > + targets 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
