[Bug libc/22624] MIPS setjmp() saves incorrect 'o0' register in --enable-stack-protector=all

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https://sourceware.org/bugzilla/show_bug.cgi?id=22624

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=368b6c8da9f8ae453f5d70f8a62dbf3f1b6d5995

commit 368b6c8da9f8ae453f5d70f8a62dbf3f1b6d5995
Author: Sergei Trofimovich <slyfox@gentoo.org>
Date:   Mon Dec 18 17:23:02 2017 +0000

    mips64: fix clobbering s0 in setjmp() [BZ #22624]

    When configured as --enable-stack-protector=all glibc
    inserts stack checking canary into every function
    including __sigsetjmp_aux(). Stack checking code
    ends up using s0 register to temporary hold address
    of global canary value.

    Unfortunately __sigsetjmp_aux assumes no caller' caller-save
    registers should be clobbered as it stores them as-is.

    The fix is to disable stack protection of __sigsetjmp_aux.

    Tested on the following test:

        #include <setjmp.h>
        #include <stdio.h>

        int main() {
            jmp_buf jb;
            volatile register long s0 asm ("$s0");
            s0 = 1234;
            if (setjmp(jb) == 0)
                longjmp(jb, 1);
            printf ("$s0 = %lu\n", s0);
        }

    Without the fix:
        $ qemu-mipsn32 -L . ./mips-longjmp-bug
        $s0 = 1082346228

    With the fix:
        $ qemu-mipsn32 -L . ./mips-longjmp-bug
        $s0 = 1234

        [BZ #22624]
        * sysdeps/mips/mips64/setjmp_aux.c (__sigsetjmp_aux): Use
        inhibit_stack_protector.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                        |    6 ++++++
 sysdeps/mips/mips64/setjmp_aux.c |    5 +++++
 2 files changed, 11 insertions(+), 0 deletions(-)

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