Re: [PATCH 1/3] MIPS: r2-on-r6-emu: Fix BLEZL and BGTZL identification

[Ralf Baechle <ralf@linux-mips.org>]

On Mon, Mar 13, 2017 at 04:36:35PM +0100, Aleksandar Markovic wrote:

> From: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
> 
> Fix the problem of inaccurate identification of instructions BLEZL and
> BGTZL in R2 emulation code by making sure all necessary encoding
> specifications are met.
> 
> Previously, certain R6 instructions could be identified as BLEZL or
> BGTZL. R2 emulation routine didn't take into account that both BLEZL
> and BGTZL instructions require their rt field (bits 20 to 16 of
> instruction encoding) to be 0, and that, at same time, if the value in
> that field is not 0, the encoding may represent a legitimate MIPS R6
> instruction.
> 
> This means that a problem could occur after emulation optimization,
> when emulation routine tried to pipeline emulation, picked up a next
> candidate, and subsequently misrecognized an R6 instruction as BLEZL
> or BGTZL.
> 
> It should be said that for single pass strategy, the problem does not
> happen because CPU doesn't trap on branch-compacts which share opcode
> space with BLEZL/BGTZL (but have rt field != 0, of course).
> 
> Signed-off-by: Leonid Yegoshin <leonid.yegoshin@imgtec.com>
> Signed-off-by: Miodrag Dinic <miodrag.dinic@imgtech.com>
> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtech.com>
> Reported-by: Douglas Leung <douglas.leung@imgtec.com>
> Reviewed-by: Paul Burton <paul.burton@imgtec.com>

Thanks for sorting out the review comments on v1.

Applied,

  Ralf