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@xxxxxxxxxxxxxx> --- Ralf, The jump to the delay slot combined with the unusual register usage convention taken here made it trickier than it would normally be to make a fix that does not regress -- in terms of code size -- unaffected microMIPS systems. I tried several versions and eventually I came up with this one that I believe produces the best code in all cases, at the cost of these #ifdefs. I hope they are acceptable. Please apply, Maciej linux-mips-strnlen-user-nodaddi-fix.patch Index: linux-20150524-4maxp64/arch/mips/lib/strnlen_user.S =================================================================== --- linux-20150524-4maxp64.orig/arch/mips/lib/strnlen_user.S +++ linux-20150524-4maxp64/arch/mips/lib/strnlen_user.S @@ -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
