[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>

arch/i386/kernel/vsyscall-sigreturn.S

@@ -44,7 +44,7 @@ __kernel_rt_sigreturn:
 .LSTARTCIEDLSI1:
 	.long 0			/* CIE ID */
 	.byte 1			/* Version number */
-	.string "zR"		/* NUL-terminated augmentation string */
+	.string "zRS"		/* NUL-terminated augmentation string */
 	.uleb128 1		/* Code alignment factor */
 	.sleb128 -4		/* Data alignment factor */
 	.byte 8			/* Return address register column */

arch/powerpc/kernel/vdso32/sigtramp.S

@@ -261,7 +261,7 @@ V_FUNCTION_END(__kernel_sigtramp_rt32)
 .Lcie_start:
 	.long 0			/* CIE ID */
 	.byte 1			/* Version number */
-	.string "zR"		/* NUL-terminated augmentation string */
+	.string "zRS"		/* NUL-terminated augmentation string */
 	.uleb128 4		/* Code alignment factor */
 	.sleb128 -4		/* Data alignment factor */
 	.byte 67		/* Return address register column, ap */

arch/powerpc/kernel/vdso64/sigtramp.S

@@ -263,7 +263,7 @@ V_FUNCTION_END(__kernel_sigtramp_rt64)
 .Lcie_start:
 	.long 0			/* CIE ID */
 	.byte 1			/* Version number */
-	.string "zR"		/* NUL-terminated augmentation string */
+	.string "zRS"		/* NUL-terminated augmentation string */
 	.uleb128 4		/* Code alignment factor */
 	.sleb128 -8		/* Data alignment factor */
 	.byte 67		/* Return address register column, ap */

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