On Fri, Jan 21, 2022 at 11:23 AM Richard Sandiford via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > soe...@soeren-tempel.net writes: > > From: Sören Tempel <soe...@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 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 <soe...@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. > > Thanks, pushed to trunk.
This broke GCC bootstrap on Linux/i686: https://gcc.gnu.org/pipermail/gcc-regression/2022-January/076271.html > Richard > > > --- > > This version of the patch fixes a few codingstyle violations pointed out > > to me by Richard Sandiford, it does not include any functional changes > > compared to previous versions of this patch. > > > > gcc/common/config/s390/s390-common.cc | 14 ++++++++++---- > > gcc/config/i386/gnu-user-common.h | 5 +++-- > > gcc/config/i386/gnu.h | 5 ++++- > > 3 files changed, 17 insertions(+), 7 deletions(-) > > > > diff --git a/gcc/common/config/s390/s390-common.cc > > b/gcc/common/config/s390/s390-common.cc > > index 6ed2f89f3d0..547b0826f93 100644 > > --- a/gcc/common/config/s390/s390-common.cc > > +++ b/gcc/common/config/s390/s390-common.cc > > @@ -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 > > diff --git a/gcc/config/i386/gnu-user-common.h > > b/gcc/config/i386/gnu-user-common.h > > index 23b54c5be52..7525f788a9c 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 && OPTION_GLIBC > > #define TARGET_CAN_SPLIT_STACK > > #endif > > diff --git a/gcc/config/i386/gnu.h b/gcc/config/i386/gnu.h > > index 401e60c9a02..daa505a5d45 100644 > > --- a/gcc/config/i386/gnu.h > > +++ b/gcc/config/i386/gnu.h > > @@ -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 -- H.J.
