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MIPS: strnlen_user.S: Fix a CPU_DADDI_WORKAROUNDS regression

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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>
This commit is contained in:
Maciej W. Rozycki 2015-05-28 17:46:49 +01:00 committed by Ralf Baechle
parent 57b4175823
commit c4fca4fdea
1 changed files with 13 additions and 2 deletions
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15
arch/mips/lib/strnlen_user.S
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@ -34,7 +34,12 @@ LEAF(__strnlen_\func\()_asm)
FEXPORT(__strnlen_\func\()_nocheck_asm)
move v0, a0
PTR_ADDU a1, a0 # stop pointer
1: beq v0, a1, 1f # limit reached?
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
@ -42,7 +47,13 @@ FEXPORT(__strnlen_\func\()_nocheck_asm)
.endif
.set noreorder
bnez t0, 1b
1: PTR_ADDIU v0, 1
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