On Mon, 7 Nov 2016, Leonid Yegoshin wrote:
> MIPS R2 emulation doesn't take into account that BLEZL and BGTZL instructions
> require register RT = 0. If it is not zero it can be some legitimate MIPS R6
> instruction.
Well, it *is* rather than just can be -- one of BLEZC/BGEZC/BGEC or
BGTZC/BLTZC/BLTC, respectively, according to the bit patterns in RS/RT,
all these instructions being compact branches, so we can stop emulation
rather than decoding them.
Also please line-wrap your description at 75 columns, as per
Documentation/SubmittingPatches.
> diff --git a/arch/mips/kernel/mips-r2-to-r6-emul.c b/arch/mips/kernel/mips-r2-to-r6-emul.c
> index 22dedd62818a..b0c86b08c0b9 100644
> --- a/arch/mips/kernel/mips-r2-to-r6-emul.c
> +++ b/arch/mips/kernel/mips-r2-to-r6-emul.c
> @@ -919,6 +919,7 @@ int mipsr2_decoder(struct pt_regs *regs, u32 inst, unsigned long *fcr31)
> BUG();
> return SIGEMT;
> }
> + err = 0;
> pr_debug("Emulating the 0x%08x R2 instruction @ 0x%08lx (pass=%d))\n",
> inst, epc, pass);
Is this because of BRANCH_LIKELY_TAKEN? It has to be a separate patch
then, with a suitable description.
> @@ -1096,10 +1097,16 @@ int mipsr2_decoder(struct pt_regs *regs, u32 inst,
> unsigned long *fcr31)
> }
> break;
>
> - case beql_op:
> - case bnel_op:
> case blezl_op:
> case bgtzl_op:
> + /* return MIPS R6 instruction to CPU execution */
> + if (MIPSInst_RT(inst)) {
> + err = SIGILL;
> + break;
> + }
Please add:
/* Fall through. */
here so that it is clear it's not a bug; also GCC 7 will catch such cases
and issue warnings, which I expect according to our settings will cause a
build failure here if this is missing.
> +
> + case beql_op:
> + case bnel_op:
This part looks fine to me otherwise.
Maciej
