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ARM: memmove: use frame pointer as unwind anchor

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The memmove routine is a bit unusual in the way it manages the stack
pointer: depending on the execution path through the function, the SP
assumes different values as different subsets of the register file are
preserved and restored again. This is problematic when it comes to EHABI
unwind info, as it is not instruction accurate, and does not allow
tracking the SP value as it changes.

Commit 207a6cb069 ("ARM: 8224/1: Add unwinding support for memmove
function") addressed this by carving up the function in different chunks
as far as the unwinder is concerned, and keeping a set of unwind
directives for each of them, each corresponding with the state of the
stack pointer during execution of the chunk in question. This not only
duplicates unwind info unnecessarily, but it also complicates unwinding
the stack upon overflow.

Instead, let's do what the compiler does when the SP is updated halfway
through a function, which is to use a frame pointer and emit the
appropriate unwind directives to communicate this to the unwinder.

Note that Thumb-2 uses R7 for this, while ARM uses R11 aka FP. So let's
avoid touching R7 in the body of the function, so that Thumb-2 can use
it as the frame pointer. R11 was not modified in the first place.

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
This commit is contained in:
Ard Biesheuvel 2021-10-04 11:29:11 +02:00
parent ba999a0402
commit ccb81601ac
1 changed files with 20 additions and 40 deletions
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60
arch/arm/lib/memmove.S
View File

@ -31,12 +31,13 @@ WEAK(memmove)
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
UNWIND( .save {r0, r4, fpreg, lr} )
stmfd sp!, {r0, r4, UNWIND(fpreg,) lr}
UNWIND( .setfp fpreg, sp )
UNWIND( mov fpreg, sp )
add r1, r1, r2
add r0, r0, r2
subs r2, r2, #4
@ -48,12 +49,7 @@ WEAK(memmove)
bne 10f
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
stmfd sp!, {r5, r6, r8, r9}
blt 5f
CALGN( ands ip, r0, #31 )
@ -72,9 +68,9 @@ WEAK(memmove)
PLD( pld [r1, #-96] )
3: PLD( pld [r1, #-128] )
4: ldmdb r1!, {r3, r4, r5, r6, r7, r8, ip, lr}
4: ldmdb r1!, {r3, r4, r5, r6, r8, r9, ip, lr}
subs r2, r2, #32
stmdb r0!, {r3, r4, r5, r6, r7, r8, ip, lr}
stmdb r0!, {r3, r4, r5, r6, r8, r9, ip, lr}
bge 3b
PLD( cmn r2, #96 )
PLD( bge 4b )
@ -88,8 +84,8 @@ WEAK(memmove)
W(ldr) r4, [r1, #-4]!
W(ldr) r5, [r1, #-4]!
W(ldr) r6, [r1, #-4]!
W(ldr) r7, [r1, #-4]!
W(ldr) r8, [r1, #-4]!
W(ldr) r9, [r1, #-4]!
W(ldr) lr, [r1, #-4]!
add pc, pc, ip
@ -99,17 +95,13 @@ WEAK(memmove)
W(str) r4, [r0, #-4]!
W(str) r5, [r0, #-4]!
W(str) r6, [r0, #-4]!
W(str) r7, [r0, #-4]!
W(str) r8, [r0, #-4]!
W(str) r9, [r0, #-4]!
W(str) lr, [r0, #-4]!
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
7: ldmfd sp!, {r5, r6, r8, r9}
8: movs r2, r2, lsl #31
ldrbne r3, [r1, #-1]!
@ -118,7 +110,7 @@ WEAK(memmove)
strbne r3, [r0, #-1]!
strbcs r4, [r0, #-1]!
strbcs ip, [r0, #-1]
ldmfd sp!, {r0, r4, pc}
ldmfd sp!, {r0, r4, UNWIND(fpreg,) pc}
9: cmp ip, #2
ldrbgt r3, [r1, #-1]!
@ -137,13 +129,10 @@ WEAK(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
@ -152,12 +141,7 @@ WEAK(memmove)
CALGN( subcc r2, r2, ip )
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
11: stmfd sp!, {r5, r6, r8 - r10}
PLD( pld [r1, #-4] )
PLD( subs r2, r2, #96 )
@ -167,35 +151,31 @@ WEAK(memmove)
PLD( pld [r1, #-96] )
12: PLD( pld [r1, #-128] )
13: ldmdb r1!, {r7, r8, r9, ip}
13: ldmdb r1!, {r8, r9, r10, ip}
mov lr, r3, lspush #\push
subs r2, r2, #32
ldmdb r1!, {r3, r4, r5, r6}
orr lr, lr, ip, lspull #\pull
mov ip, ip, lspush #\push
orr ip, ip, r9, lspull #\pull
orr ip, ip, r10, lspull #\pull
mov r10, r10, lspush #\push
orr r10, r10, r9, lspull #\pull
mov r9, r9, lspush #\push
orr r9, r9, r8, lspull #\pull
mov r8, r8, lspush #\push
orr r8, r8, r7, lspull #\pull
mov r7, r7, lspush #\push
orr r7, r7, r6, lspull #\pull
orr r8, r8, r6, lspull #\pull
mov r6, r6, lspush #\push
orr r6, r6, r5, lspull #\pull
mov r5, r5, lspush #\push
orr r5, r5, r4, lspull #\pull
mov r4, r4, lspush #\push
orr r4, r4, r3, lspull #\pull
stmdb r0!, {r4 - r9, ip, lr}
stmdb r0!, {r4 - r6, r8 - r10, ip, lr}
bge 12b
PLD( cmn r2, #96 )
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
ldmfd sp!, {r5, r6, r8 - r10}
14: ands ip, r2, #28
beq 16f
@ -211,7 +191,6 @@ WEAK(memmove)
16: add r1, r1, #(\pull / 8)
b 8b
UNWIND( .fnend )
.endm
@ -222,5 +201,6 @@ WEAK(memmove)
18: backward_copy_shift push=24 pull=8
UNWIND( .fnend )
ENDPROC(memmove)
ENDPROC(__memmove)