diff mbox

PowerPC64 power8 strncpy cfi fixes

Message ID 20171020130627.GC27132@bubble.grove.modra.org
State Committed
Delegated to: Tulio Magno Quites Machado Filho
Headers

Commit Message

Alan Modra Oct. 20, 2017, 1:06 p.m. UTC 
  cfi info for stack adjust needs to be on the insn doing the adjust.
cfi describing register saves can be anywhere after the save insn but
before the reg is altered.  Fewer locations with cfi result in smaller
cfi programs and possibly slightly faster exception handling.  Thus
the LR cfi_offset move.

The idea behind ajusting sp after restoring regs is to break a
register dependency chain, in this case not be using r1 immediately
after it is modified.

The missing LR cfi_restore meant that code after the blr,
unaligned_lt_16 and other labels, would have cfi that said LR was at
cfa+16, but that code is reached without LR being saved.

	* sysdeps/powerpc/powerpc64/power8/strncpy.S: Move LR cfi.
	Adjust stack after restoring regs.  Add missing LR cfi_restore.

Comments

Tulio Magno Quites Machado Filho Oct. 21, 2017, 12:09 a.m. UTC | #1 
Alan Modra <amodra@gmail.com> writes:

> cfi info for stack adjust needs to be on the insn doing the adjust.
> cfi describing register saves can be anywhere after the save insn but
> before the reg is altered.  Fewer locations with cfi result in smaller
> cfi programs and possibly slightly faster exception handling.  Thus
> the LR cfi_offset move.
>
> The idea behind ajusting sp after restoring regs is to break a
> register dependency chain, in this case not be using r1 immediately
> after it is modified.
>
> The missing LR cfi_restore meant that code after the blr,
> unaligned_lt_16 and other labels, would have cfi that said LR was at
> cfa+16, but that code is reached without LR being saved.
>
> 	* sysdeps/powerpc/powerpc64/power8/strncpy.S: Move LR cfi.
> 	Adjust stack after restoring regs.  Add missing LR cfi_restore.

Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
diff mbox

Patch

diff --git a/sysdeps/powerpc/powerpc64/power8/strncpy.S b/sysdeps/powerpc/powerpc64/power8/strncpy.S
index 150290a..c55e62d 100644
--- a/sysdeps/powerpc/powerpc64/power8/strncpy.S
+++ b/sysdeps/powerpc/powerpc64/power8/strncpy.S
@@ -241,23 +241,18 @@  L(zero_pad_start_1):
 	/* Save the link register.  */
 	mflr	r0
 	std	r0,16(r1)
-	cfi_offset(lr, 16)
 
 	/* Create the stack frame.  */
 	stdu	r1,-FRAMESIZE(r1)
 	cfi_adjust_cfa_offset(FRAMESIZE)
+	cfi_offset(lr, 16)
 
 	bl	MEMSET
 #ifndef MEMSET_is_local
 	nop
 #endif
 
-	/* Restore the stack frame.  */
-	addi	r1,r1,FRAMESIZE
-	cfi_adjust_cfa_offset(-FRAMESIZE)
-	/* Restore the link register.  */
-	ld	r0,16(r1)
-	mtlr	r0
+	ld	r0,FRAMESIZE+16(r1)
 
 #ifndef USE_AS_STPNCPY
 	mr	r3,r30       /* Restore the return value of strncpy, i.e.:
@@ -266,12 +261,18 @@  L(zero_pad_start_1):
 #endif
 
 	/* Restore non-volatile registers and return.  */
-	ld	r26,-48(r1)
-	ld	r27,-40(r1)
-	ld	r28,-32(r1)
-	ld	r29,-24(r1)
-	ld	r30,-16(r1)
-	ld	r31,-8(r1)
+	ld	r26,FRAMESIZE-48(r1)
+	ld	r27,FRAMESIZE-40(r1)
+	ld	r28,FRAMESIZE-32(r1)
+	ld	r29,FRAMESIZE-24(r1)
+	ld	r30,FRAMESIZE-16(r1)
+	ld	r31,FRAMESIZE-8(r1)
+	/* Restore the stack frame.  */
+	addi	r1,r1,FRAMESIZE
+	cfi_adjust_cfa_offset(-FRAMESIZE)
+	/* Restore the link register.  */
+	mtlr	r0
+	cfi_restore(lr)
 	blr
 
 	/* The common case where [src]+16 will not cross a 4K page boundary.