[COMMITTED] alpha: Fix signal thunk unwind info

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[COMMITTED] alpha: Fix signal thunk unwind info

Richard Henderson
---
I'm still testing this same patch applied to 2.18.  I don't plan on
backporting it further.  Gentoo can do that if it wishes, but I hope
most of their users will update all the way to the most recent.


r~


 ports/ChangeLog.alpha                              |  5 +++++
 ports/sysdeps/unix/sysv/linux/alpha/rt_sigaction.S | 18 ++++++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/ports/ChangeLog.alpha b/ports/ChangeLog.alpha
index 07f5dfb..8f97951 100644
--- a/ports/ChangeLog.alpha
+++ b/ports/ChangeLog.alpha
@@ -1,3 +1,8 @@
+2013-11-16  Richard Henderson  <[hidden email]>
+
+ * sysdeps/unix/sysv/linux/alpha/rt_sigaction.S: Include a nop
+ before each signal thunk.
+
 2013-10-30  Mike Frysinger  <[hidden email]>
 
  * sysdeps/alpha/configure.in: Moved to ...
diff --git a/ports/sysdeps/unix/sysv/linux/alpha/rt_sigaction.S b/ports/sysdeps/unix/sysv/linux/alpha/rt_sigaction.S
index 3d291fd..6efa738 100644
--- 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
--
1.8.3.1