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linux/arch/arm/lib/copy_template.S
Ard Biesheuvel ba999a0402 ARM: memcpy: use frame pointer as unwind anchor 
The memcpy template 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 279f487e0b ("ARM: 8225/1: Add unwinding support for memory
copy functions") 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 template, 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
2021-12-03 15:11:32 +01:00

274 lines
6.2 KiB
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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* linux/arch/arm/lib/copy_template.s
*
* Code template for optimized memory copy functions
*
* Author: Nicolas Pitre
* Created: Sep 28, 2005
* Copyright: MontaVista Software, Inc.
*/
/*
* Theory of operation
* -------------------
*
* This file provides the core code for a forward memory copy used in
* the implementation of memcopy(), copy_to_user() and copy_from_user().
*
* The including file must define the following accessor macros
* according to the need of the given function:
*
* ldr1w ptr reg abort
*
* This loads one word from 'ptr', stores it in 'reg' and increments
* 'ptr' to the next word. The 'abort' argument is used for fixup tables.
*
* ldr4w ptr reg1 reg2 reg3 reg4 abort
* ldr8w ptr, reg1 reg2 reg3 reg4 reg5 reg6 reg7 reg8 abort
*
* This loads four or eight words starting from 'ptr', stores them
* in provided registers and increments 'ptr' past those words.
* The'abort' argument is used for fixup tables.
*
* ldr1b ptr reg cond abort
*
* Similar to ldr1w, but it loads a byte and increments 'ptr' one byte.
* It also must apply the condition code if provided, otherwise the
* "al" condition is assumed by default.
*
* str1w ptr reg abort
* str8w ptr reg1 reg2 reg3 reg4 reg5 reg6 reg7 reg8 abort
* str1b ptr reg cond abort
*
* Same as their ldr* counterparts, but data is stored to 'ptr' location
* rather than being loaded.
*
* enter reg1 reg2
*
* Preserve the provided registers on the stack plus any additional
* data as needed by the implementation including this code. Called
* upon code entry.
*
* usave reg1 reg2
*
* Unwind annotation macro is corresponding for 'enter' macro.
* It tell unwinder that preserved some provided registers on the stack
* and additional data by a prior 'enter' macro.
*
* exit reg1 reg2
*
* Restore registers with the values previously saved with the
* 'preserv' macro. Called upon code termination.
*
* LDR1W_SHIFT
* STR1W_SHIFT
*
* Correction to be applied to the "ip" register when branching into
* the ldr1w or str1w instructions (some of these macros may expand to
* than one 32bit instruction in Thumb-2)
*/
UNWIND( .fnstart )
enter r4, UNWIND(fpreg,) lr
UNWIND( .setfp fpreg, sp )
UNWIND( mov fpreg, sp )
subs r2, r2, #4
blt 8f
ands ip, r0, #3
PLD( pld [r1, #0] )
bne 9f
ands ip, r1, #3
bne 10f
1: subs r2, r2, #(28)
stmfd sp!, {r5, r6, r8, r9}
blt 5f
CALGN( ands ip, r0, #31 )
CALGN( rsb r3, ip, #32 )
CALGN( sbcsne r4, r3, r2 ) @ C is always set here
CALGN( bcs 2f )
CALGN( adr r4, 6f )
CALGN( subs r2, r2, r3 ) @ C gets set
CALGN( add pc, r4, ip )
PLD( pld [r1, #0] )
2: PLD( subs r2, r2, #96 )
PLD( pld [r1, #28] )
PLD( blt 4f )
PLD( pld [r1, #60] )
PLD( pld [r1, #92] )
3: PLD( pld [r1, #124] )
4: ldr8w r1, r3, r4, r5, r6, r8, r9, ip, lr, abort=20f
subs r2, r2, #32
str8w r0, r3, r4, r5, r6, r8, r9, ip, lr, abort=20f
bge 3b
PLD( cmn r2, #96 )
PLD( bge 4b )
5: ands ip, r2, #28
rsb ip, ip, #32
#if LDR1W_SHIFT > 0
lsl ip, ip, #LDR1W_SHIFT
#endif
addne pc, pc, ip @ C is always clear here
b 7f
6:
.rept (1 << LDR1W_SHIFT)
W(nop)
.endr
ldr1w r1, r3, abort=20f
ldr1w r1, r4, abort=20f
ldr1w r1, r5, abort=20f
ldr1w r1, r6, abort=20f
ldr1w r1, r8, abort=20f
ldr1w r1, r9, abort=20f
ldr1w r1, lr, abort=20f
#if LDR1W_SHIFT < STR1W_SHIFT
lsl ip, ip, #STR1W_SHIFT - LDR1W_SHIFT
#elif LDR1W_SHIFT > STR1W_SHIFT
lsr ip, ip, #LDR1W_SHIFT - STR1W_SHIFT
#endif
add pc, pc, ip
nop
.rept (1 << STR1W_SHIFT)
W(nop)
.endr
str1w r0, r3, abort=20f
str1w r0, r4, abort=20f
str1w r0, r5, abort=20f
str1w r0, r6, abort=20f
str1w r0, r8, abort=20f
str1w r0, r9, abort=20f
str1w r0, lr, abort=20f
CALGN( bcs 2b )
7: ldmfd sp!, {r5, r6, r8, r9}
8: movs r2, r2, lsl #31
ldr1b r1, r3, ne, abort=21f
ldr1b r1, r4, cs, abort=21f
ldr1b r1, ip, cs, abort=21f
str1b r0, r3, ne, abort=21f
str1b r0, r4, cs, abort=21f
str1b r0, ip, cs, abort=21f
exit r4, UNWIND(fpreg,) pc
9: rsb ip, ip, #4
cmp ip, #2
ldr1b r1, r3, gt, abort=21f
ldr1b r1, r4, ge, abort=21f
ldr1b r1, lr, abort=21f
str1b r0, r3, gt, abort=21f
str1b r0, r4, ge, abort=21f
subs r2, r2, ip
str1b r0, lr, abort=21f
blt 8b
ands ip, r1, #3
beq 1b
10: bic r1, r1, #3
cmp ip, #2
ldr1w r1, lr, abort=21f
beq 17f
bgt 18f
.macro forward_copy_shift pull push
subs r2, r2, #28
blt 14f
CALGN( ands ip, r0, #31 )
CALGN( rsb ip, ip, #32 )
CALGN( sbcsne r4, ip, r2 ) @ C is always set here
CALGN( subcc r2, r2, ip )
CALGN( bcc 15f )
11: stmfd sp!, {r5, r6, r8 - r10}
PLD( pld [r1, #0] )
PLD( subs r2, r2, #96 )
PLD( pld [r1, #28] )
PLD( blt 13f )
PLD( pld [r1, #60] )
PLD( pld [r1, #92] )
12: PLD( pld [r1, #124] )
13: ldr4w r1, r4, r5, r6, r8, abort=19f
mov r3, lr, lspull #\pull
subs r2, r2, #32
ldr4w r1, r9, r10, ip, lr, abort=19f
orr r3, r3, r4, lspush #\push
mov r4, r4, lspull #\pull
orr r4, r4, r5, lspush #\push
mov r5, r5, lspull #\pull
orr r5, r5, r6, lspush #\push
mov r6, r6, lspull #\pull
orr r6, r6, r8, lspush #\push
mov r8, r8, lspull #\pull
orr r8, r8, r9, lspush #\push
mov r9, r9, lspull #\pull
orr r9, r9, r10, lspush #\push
mov r10, r10, lspull #\pull
orr r10, r10, ip, lspush #\push
mov ip, ip, lspull #\pull
orr ip, ip, lr, lspush #\push
str8w r0, r3, r4, r5, r6, r8, r9, r10, ip, abort=19f
bge 12b
PLD( cmn r2, #96 )
PLD( bge 13b )
ldmfd sp!, {r5, r6, r8 - r10}
14: ands ip, r2, #28
beq 16f
15: mov r3, lr, lspull #\pull
ldr1w r1, lr, abort=21f
subs ip, ip, #4
orr r3, r3, lr, lspush #\push
str1w r0, r3, abort=21f
bgt 15b
CALGN( cmp r2, #0 )
CALGN( bge 11b )
16: sub r1, r1, #(\push / 8)
b 8b
.endm
forward_copy_shift pull=8 push=24
17: forward_copy_shift pull=16 push=16
18: forward_copy_shift pull=24 push=8
UNWIND( .fnend )
/*
* Abort preamble and completion macros.
* If a fixup handler is required then those macros must surround it.
* It is assumed that the fixup code will handle the private part of
* the exit macro.
*/
.macro copy_abort_preamble
19: ldmfd sp!, {r5, r6, r8 - r10}
b 21f
20: ldmfd sp!, {r5, r6, r8, r9}
21:
.endm
.macro copy_abort_end
ldmfd sp!, {r4, UNWIND(fpreg,) pc}
.endm
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