[PATCH] Mark unwind info for signal trampolines in vDSOs

Mark unwind info for signal trampolines using the new S augmentation flag
introduced in: http://gcc.gnu.org/PR26208.

GCC 4.2 (or patched earlier GCC) will be able to special case unwinding
through frames right above signal trampolines.  As the augmentations start
with z flag and S is at the very end of the augmentation string, older GCCs
will just skip the S flag as unknown (that's why an augmentation flag was
chosen over say a new CFA opcode).

Signed-off-by: Jakub Jelinek <jakub@redhat.com>
Cc: Andi Kleen <ak@muc.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 21 insertions, 2 deletions

diff --git a/arch/x86_64/ia32/vsyscall-sigreturn.S b/arch/x86_64/ia32/vsyscall-sigreturn.S
index d90321fe9bba..1384367cdbe1 100644
--- a/arch/x86_64/ia32/vsyscall-sigreturn.S
+++ b/arch/x86_64/ia32/vsyscall-sigreturn.S
@@ -32,9 +32,28 @@ __kernel_rt_sigreturn:
         .size __kernel_rt_sigreturn,.-.LSTART_rt_sigreturn
 
         .section .eh_frame,"a",@progbits
+.LSTARTFRAMES:
+        .long .LENDCIES-.LSTARTCIES
+.LSTARTCIES:
+        .long 0                 /* CIE ID */
+        .byte 1                 /* Version number */
+        .string "zRS"           /* NUL-terminated augmentation string */
+        .uleb128 1              /* Code alignment factor */
+        .sleb128 -4             /* Data alignment factor */
+        .byte 8                 /* Return address register column */
+        .uleb128 1              /* Augmentation value length */
+        .byte 0x1b              /* DW_EH_PE_pcrel|DW_EH_PE_sdata4. */
+        .byte 0x0c              /* DW_CFA_def_cfa */
+        .uleb128 4
+        .uleb128 4
+        .byte 0x88              /* DW_CFA_offset, column 0x8 */
+        .uleb128 1
+        .align 4
+.LENDCIES:
+
         .long .LENDFDE2-.LSTARTFDE2     /* Length FDE */
 .LSTARTFDE2:
-        .long .LSTARTFDE2-.LSTARTFRAME  /* CIE pointer */
+        .long .LSTARTFDE2-.LSTARTFRAMES /* CIE pointer */
         /* HACK: The dwarf2 unwind routines will subtract 1 from the
            return address to get an address in the middle of the
            presumed call instruction.  Since we didn't get here via
@@ -97,7 +116,7 @@ __kernel_rt_sigreturn:
 
         .long .LENDFDE3-.LSTARTFDE3     /* Length FDE */
 .LSTARTFDE3:
-        .long .LSTARTFDE3-.LSTARTFRAME  /* CIE pointer */
+        .long .LSTARTFDE3-.LSTARTFRAMES /* CIE pointer */
         /* HACK: See above wrt unwind library assumptions.  */
         .long .LSTART_rt_sigreturn-1-.  /* PC-relative start address */
         .long .LEND_rt_sigreturn-.LSTART_rt_sigreturn+1