alpha: Fix signal thunk unwind info

2013-11-16  Richard Henderson  <rth@redhat.com>

	* sysdeps/unix/sysv/linux/alpha/rt_sigaction.S: Include a nop
	before each signal thunk.

URL: https://bugs.gentoo.org/480740
URL: https://sourceware.org/ml/libc-ports/2013-11/msg00000.html

(cherry picked from commit 027e32bd42314e17095ba39df82ef293f4a72c09)

diff --git a/ports/sysdeps/unix/sysv/linux/alpha/rt_sigaction.S b/ports/sysdeps/unix/sysv/linux/alpha/rt_sigaction.S
index 3d291fd0b4ba253cccd00b8d7900707737ccf759..6efa7386d58a9fef153ff455b76dc8093c39f2b6 100644 (file)
--- a/ports/sysdeps/unix/sysv/linux/alpha/rt_sigaction.S
+++ b/ports/sysdeps/unix/sysv/linux/alpha/rt_sigaction.S
@@ -83,14 +83,21 @@ PSEUDO_END(__syscall_rt_sigaction)
        cfi_offset (64, \base + 2 * 8)
        .endm
 
-       .align  4
-
        cfi_startproc
        cfi_return_column (64)
        .cfi_signal_frame
        SIGCONTEXT_REGS -648
-
        cfi_def_cfa_offset (648)
+
+       /* While this frame is marked as a signal frame, that only applies
+          to how this return address is handled for the outer frame.
+          The return address that arrived here, from the inner frame, is
+          not marked as a signal frame and so the unwinder still tries to
+          subtract 1 to examine the presumed call insn.  Thus we must
+          extend the unwind info to a nop before the start.  */
+       nop
+       .align 4
+
 __syscall_sigreturn:
        mov     sp, a0
        ldi     v0, __NR_sigreturn
@@ -98,8 +105,11 @@ __syscall_sigreturn:
        .size   __syscall_sigreturn, .-__syscall_sigreturn
        .type   __syscall_sigreturn, @function
 
-       .align 4
+       /* See above wrt including the nop.  */
        cfi_def_cfa_offset (176 + 648)
+       nop
+       .align 4
+
 __syscall_rt_sigreturn:
        mov     sp,a0
        ldi     v0,__NR_rt_sigreturn