Re: [PATCH-for-5.2] target/mips: Report unimplemented cache() operations

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 6 Aug 2020 at 21:31, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> On 8/6/20 8:01 PM, Jiaxun Yang wrote:
> > 在 2020/8/6 下午8:26, Philippe Mathieu-Daudé 写道:
> >> We only implement the Index[Store/Load]Tag from the 'cache' opcode.
> >> Instead of ignoring the other cache operations, report them as
> >> unimplemented.
> >
> > Hmm, I don't think we have anything to do with Invalidate/Writeback etc.
> > opcodes
> > in QEMU. Why do we log this?
>
> I'm noticed this code is run on Linux 3.3.8 (4KEc):
>
>     8880:       3082000f        andi    v0,a0,0xf
>     8884:       10800008        beqz    a0,88a8
>     8888:       00a21021        addu    v0,a1,v0
>     888c:       08002227        j       889c
>     8890:       00001821        move    v1,zero
>     8894:       bcf90000        cache   0x19,0(a3)
>     8898:       24630010        addiu   v1,v1,16
>     889c:       0062302b        sltu    a2,v1,v0
>     88a0:       14c0fffc        bnez    a2,8894
>     88a4:       00833821        addu    a3,a0,v1
>     88a8:       03e00008        jr      ra
>     88ac:       00000000        nop
>
> Why silently ignore the opcode is not implemented instead of logging it?

I think the question is whether the opcode is supposed to have
some behaviour which we're not implementing, or whether "no-op"
is the correct behaviour for it (which it usually is for
cache invalidate type operations; compare the way the Arm
cache ops like IC_IALLU are just ARM_CP_NOP ops).

thanks
-- PMM