ARM: memset: clean up unwind annotations

The memset implementation carves up the code in different sections, each
covered with their own unwind info. In this case, it is done in a way
similar to how the compiler might do it, to disambiguate between parts
where the return address is in LR and the SP is unmodified, and parts
where a stack frame is live, and the unwinder needs to know the size of
the stack frame and the location of the return address within it.

Only the placement of the unwind directives is slightly odd: the stack
pushes are placed in the wrong sections, which may confuse the unwinder
when attempting to unwind with PC pointing at the stack push in
question.

So let's fix this up, by reordering the directives and instructions as
appropriate.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Keith Packard <keithpac@amazon.com>
Tested-by: Marc Zyngier <maz@kernel.org>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M

diff --git a/arch/arm/lib/memset.S b/arch/arm/lib/memset.S
index 9817cb2..d71ab61 100644 (file)
--- a/arch/arm/lib/memset.S
+++ b/arch/arm/lib/memset.S
@@ -28,16 +28,16 @@ UNWIND( .fnstart         )
        mov     r3, r1
 7:     cmp     r2, #16
        blt     4f
+UNWIND( .fnend              )
 
 #if ! CALGN(1)+0
 
 /*
  * We need 2 extra registers for this loop - use r8 and the LR
  */
-       stmfd   sp!, {r8, lr}
-UNWIND( .fnend              )
 UNWIND( .fnstart            )
 UNWIND( .save {r8, lr}      )
+       stmfd   sp!, {r8, lr}
        mov     r8, r1
        mov     lr, r3
 
@@ -66,10 +66,9 @@ UNWIND( .fnend              )
  * whole cache lines at once.
  */
 
-       stmfd   sp!, {r4-r8, lr}
-UNWIND( .fnend                 )
 UNWIND( .fnstart               )
 UNWIND( .save {r4-r8, lr}      )
+       stmfd   sp!, {r4-r8, lr}
        mov     r4, r1
        mov     r5, r3
        mov     r6, r1