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

From: Jiaxun Yang
Subject: Re: [PATCH-for-5.2] target/mips: Report unimplemented cache() operations
Date: Fri, 7 Aug 2020 15:57:11 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0

在 2020/8/7 上午4:51, Peter Maydell 写道:
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
Hmm, I don't think we have anything to do with Invalidate/Writeback etc.
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).
Probably we should skip Inv & WB opcode and log other undefined ops?

Otherwise the log may be flushed by Cache ops.


- Jiaxun

-- PMM

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