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.

1 files changed, 6 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index d290d60..4a71643 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2017-12-18  Sergei Trofimovich  <slyfox@gentoo.org>
+
+	[BZ #22624]
+	* sysdeps/mips/mips64/setjmp_aux.c (__sigsetjmp_aux): Use
+	inhibit_stack_protector.
+
 2017-12-18  Dmitry V. Levin  <ldv@altlinux.org>
 
 	[BZ #22627]