linux/arch/mips/lib/strnlen_user.S
Maciej W. Rozycki c4fca4fdea MIPS: strnlen_user.S: Fix a CPU_DADDI_WORKAROUNDS regression
Correct a regression introduced with 8453eebd [MIPS: Fix strnlen_user()
return value in case of overlong strings.] causing assembler warnings
and broken code generated in __strnlen_kernel_nocheck_asm:

arch/mips/lib/strnlen_user.S: Assembler messages:
arch/mips/lib/strnlen_user.S:64: Warning: Macro instruction expanded into multiple instructions in a branch delay slot

with the CPU_DADDI_WORKAROUNDS option set, resulting in the function
looping indefinitely upon mounting NFS root.

Use conditional assembly to avoid a microMIPS code size regression.
Using $at unconditionally would cause such a regression as there are no
16-bit instruction encodings available for ALU operations using this
register.  Using $v1 unconditionally would produce short microMIPS
encodings, but would prevent this register from being used across calls
to this function.

The extra LI operation introduced is free, replacing a NOP originally
scheduled into the delay slot of the branch that follows.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10205/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2015-05-29 20:23:58 +02:00

84 lines
1.8 KiB
ArmAsm

/*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (c) 1996, 1998, 1999, 2004 by Ralf Baechle
* Copyright (c) 1999 Silicon Graphics, Inc.
*/
#include <asm/asm.h>
#include <asm/asm-offsets.h>
#include <asm/regdef.h>
#define EX(insn,reg,addr,handler) \
9: insn reg, addr; \
.section __ex_table,"a"; \
PTR 9b, handler; \
.previous
/*
* Return the size of a string including the ending NUL character up to a
* maximum of a1 or 0 in case of error.
*
* Note: for performance reasons we deliberately accept that a user may
* make strlen_user and strnlen_user access the first few KSEG0
* bytes. There's nothing secret there. On 64-bit accessing beyond
* the maximum is a tad hairier ...
*/
.macro __BUILD_STRNLEN_ASM func
LEAF(__strnlen_\func\()_asm)
LONG_L v0, TI_ADDR_LIMIT($28) # pointer ok?
and v0, a0
bnez v0, .Lfault\@
FEXPORT(__strnlen_\func\()_nocheck_asm)
move v0, a0
PTR_ADDU a1, a0 # stop pointer
1:
#ifdef CONFIG_CPU_DADDI_WORKAROUNDS
.set noat
li AT, 1
#endif
beq v0, a1, 1f # limit reached?
.ifeqs "\func", "kernel"
EX(lb, t0, (v0), .Lfault\@)
.else
EX(lbe, t0, (v0), .Lfault\@)
.endif
.set noreorder
bnez t0, 1b
1:
#ifndef CONFIG_CPU_DADDI_WORKAROUNDS
PTR_ADDIU v0, 1
#else
PTR_ADDU v0, AT
.set at
#endif
.set reorder
PTR_SUBU v0, a0
jr ra
END(__strnlen_\func\()_asm)
.Lfault\@:
move v0, zero
jr ra
.endm
#ifndef CONFIG_EVA
/* Set aliases */
.global __strnlen_user_asm
.global __strnlen_user_nocheck_asm
.set __strnlen_user_asm, __strnlen_kernel_asm
.set __strnlen_user_nocheck_asm, __strnlen_kernel_nocheck_asm
#endif
__BUILD_STRNLEN_ASM kernel
#ifdef CONFIG_EVA
.set push
.set eva
__BUILD_STRNLEN_ASM user
.set pop
#endif