2014-11-24 13:46:18

by Lin Yongting

Subject: [PATCH] ARM: Add unwinding support for memmove function

The memmove function never had unwinding annotations added.
Currently, when accessing invalid pointer by memmove occurs the
backtrace shown will stop at memmove or some completely unrelated
function. Add unwinding annotations in hopes of getting a more
useful backtrace in following cases:
1. die on accessing invalid pointer by memmove
2. kprobe trapped at any instruction within memmove
3. interrupted at any instruction within memmove

Signed-off-by: Lin Yongting <[email protected]>
---
arch/arm/lib/memmove.S | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)

diff --git a/arch/arm/lib/memmove.S b/arch/arm/lib/memmove.S
index d1fc0c0..69a9d47 100644
--- a/arch/arm/lib/memmove.S
+++ b/arch/arm/lib/memmove.S
@@ -12,6 +12,7 @@

#include <linux/linkage.h>
#include <asm/assembler.h>
+#include <asm/unwind.h>

.text

@@ -27,12 +28,17 @@
*/

ENTRY(memmove)
+ UNWIND( .fnstart )

subs ip, r0, r1
cmphi r2, ip
bls memcpy

stmfd sp!, {r0, r4, lr}
+ UNWIND( .fnend )
+
+ UNWIND( .fnstart )
+ UNWIND( .save {r0, r4, lr} ) @ in first stmfd block
add r1, r1, r2
add r0, r0, r2
subs r2, r2, #4
@@ -45,6 +51,11 @@ ENTRY(memmove)

1: subs r2, r2, #(28)
stmfd sp!, {r5 - r8}
+ UNWIND( .fnend )
+
+ UNWIND( .fnstart )
+ UNWIND( .save {r0, r4, lr} )
+ UNWIND( .save {r5 - r8} ) @ in second stmfd block
blt 5f

CALGN( ands ip, r0, #31 )
@@ -97,6 +108,10 @@ ENTRY(memmove)
CALGN( bcs 2b )

7: ldmfd sp!, {r5 - r8}
+ UNWIND( .fnend ) @ end of second stmfd block
+
+ UNWIND( .fnstart )
+ UNWIND( .save {r0, r4, lr} ) @ still in first stmfd block

8: movs r2, r2, lsl #31
ldrneb r3, [r1, #-1]!
@@ -124,10 +139,13 @@ ENTRY(memmove)
ldr r3, [r1, #0]
beq 17f
blt 18f
+ UNWIND( .fnend )


.macro backward_copy_shift push pull

+ UNWIND( .fnstart )
+ UNWIND( .save {r0, r4, lr} ) @ still in first stmfd block
subs r2, r2, #28
blt 14f

@@ -137,6 +155,11 @@ ENTRY(memmove)
CALGN( bcc 15f )

11: stmfd sp!, {r5 - r9}
+ UNWIND( .fnend )
+
+ UNWIND( .fnstart )
+ UNWIND( .save {r0, r4, lr} )
+ UNWIND( .save {r5 - r9} ) @ in new second stmfd block

PLD( pld [r1, #-4] )
PLD( subs r2, r2, #96 )
@@ -171,6 +194,10 @@ ENTRY(memmove)
PLD( bge 13b )

ldmfd sp!, {r5 - r9}
+ UNWIND( .fnend ) @ end of the second stmfd block
+
+ UNWIND( .fnstart )
+ UNWIND( .save {r0, r4, lr} ) @ still in first stmfd block

14: ands ip, r2, #28
beq 16f
@@ -186,6 +213,7 @@ ENTRY(memmove)

16: add r1, r1, #(\pull / 8)
b 8b
+ UNWIND( .fnend )

.endm

--
1.7.9.5

2014-11-25 11:45:59

by Russell King - ARM Linux

Subject: Re: [PATCH] ARM: Add unwinding support for memmove function

On Mon, Nov 24, 2014 at 09:45:56PM +0800, Lin Yongting wrote:
> @@ -27,12 +28,17 @@
> */
>
> ENTRY(memmove)
> + UNWIND( .fnstart )
>
> subs ip, r0, r1
> cmphi r2, ip
> bls memcpy
>
> stmfd sp!, {r0, r4, lr}
> + UNWIND( .fnend )
> +
> + UNWIND( .fnstart )
> + UNWIND( .save {r0, r4, lr} ) @ in first stmfd block

This is pretty horrid, but I guess it's necessary due to how the unwinder
works. If no one has any objections, please drop it in the patch system
and I'll queue it for the next merge window.

Thanks.

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