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From: Jan Bobek <jan.bobek@gmail.com>
To: Richard Henderson <richard.henderson@linaro.org>, qemu-devel@nongnu.org
Cc: "Alex Bennée" <alex.bennee@linaro.org>,
	"Peter Maydell" <peter.maydell@linaro.org>,
	"Stefan Hajnoczi" <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [RISU PATCH 0/5] Fix RISU build for i386
Date: Thu, 11 Apr 2019 21:43:37 -0400	[thread overview]
Message-ID: <a82ec99d-8b5e-6898-c0a7-a3de8e2be07f@gmail.com> (raw)
In-Reply-To: <e38bf007-440c-9d6d-c837-e1e52b661075@linaro.org>

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Sorry for the delayed reply, the U.S. tax deadline has caught up with
me, so I spent the last two evenings doing my taxes. (Yuck!)

Anyway...

On 4/8/19 6:18 PM, Richard Henderson wrote:
> On 4/8/19 8:27 AM, Jan Bobek wrote:
>> 2. Note the '-std=c99' switch in the command-line above; without it,
>>    GCC defines the symbol 'i386' to 1 and the preprocessor magic for
>>    including arch-specific headers in risu.h breaks. Does anyone have
>>    an idea how to fix this in a more robust way?
> 
> Adding -U$(ARCH) to the command line is probably as good a fix as any.

I didn't know about -U, nice!

>> 3. gas (the GNU assembler) chokes on the syntax of test_i386.s; that's
>>    why I'm using nasm as the assembler above. Is that intentional? I
>>    haven't found the nasm dependency mentioned anywhere.
> 
> I think rewriting to not require nasm is better.

Agreed.

>>    Also, nasm will happily emit the UD1 opcode (0F B9) with no
>>    operands (see test_i386.s). That's a bit surprising to me, since
>>    Intel's Software Developer's Manual says UD1 has two operands; I'd
>>    expect at least a follow-up ModR/M byte. gas refuses to assemble
>>    UD1 with no operands, and gdb's disassembler gets confused when I
>>    load up the nasm's binary into risu. Is there something obvious
>>    that I'm missing?
> 
> You are not missing anything -- ud1 should require a modrm byte.
> 
> My suggestion is to use only UD1 as the "break" insn, with the different OP_*
> codes encoded into the modrm byte.

I had to laugh when I read this; this is *exactly* what I had in mind,
but then I found out there was no ModR/M byte.

>> P.S. This is my first time using git send-email, so please bear with
>>      me if something goes wrong and/or let me know how I can improve
>>      my future submissions. Thank you!
> 
> You've done well with git send-email.  ;-)

Thanks a lot! :)

-Jan


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WARNING: multiple messages have this Message-ID (diff)
From: Jan Bobek <jan.bobek@gmail.com>
To: Richard Henderson <richard.henderson@linaro.org>, qemu-devel@nongnu.org
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"Stefan Hajnoczi" <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [RISU PATCH 0/5] Fix RISU build for i386
Date: Thu, 11 Apr 2019 21:43:37 -0400	[thread overview]
Message-ID: <a82ec99d-8b5e-6898-c0a7-a3de8e2be07f@gmail.com> (raw)
Message-ID: <20190412014337.AQ9wKLbVfhnlqpz8FDMgQ_wIC_U25CPnOjkDoolOer8@z> (raw)
In-Reply-To: <e38bf007-440c-9d6d-c837-e1e52b661075@linaro.org>

[-- Attachment #1: Type: text/plain, Size: 1938 bytes --]

Sorry for the delayed reply, the U.S. tax deadline has caught up with
me, so I spent the last two evenings doing my taxes. (Yuck!)

Anyway...

On 4/8/19 6:18 PM, Richard Henderson wrote:
> On 4/8/19 8:27 AM, Jan Bobek wrote:
>> 2. Note the '-std=c99' switch in the command-line above; without it,
>>    GCC defines the symbol 'i386' to 1 and the preprocessor magic for
>>    including arch-specific headers in risu.h breaks. Does anyone have
>>    an idea how to fix this in a more robust way?
> 
> Adding -U$(ARCH) to the command line is probably as good a fix as any.

I didn't know about -U, nice!

>> 3. gas (the GNU assembler) chokes on the syntax of test_i386.s; that's
>>    why I'm using nasm as the assembler above. Is that intentional? I
>>    haven't found the nasm dependency mentioned anywhere.
> 
> I think rewriting to not require nasm is better.

Agreed.

>>    Also, nasm will happily emit the UD1 opcode (0F B9) with no
>>    operands (see test_i386.s). That's a bit surprising to me, since
>>    Intel's Software Developer's Manual says UD1 has two operands; I'd
>>    expect at least a follow-up ModR/M byte. gas refuses to assemble
>>    UD1 with no operands, and gdb's disassembler gets confused when I
>>    load up the nasm's binary into risu. Is there something obvious
>>    that I'm missing?
> 
> You are not missing anything -- ud1 should require a modrm byte.
> 
> My suggestion is to use only UD1 as the "break" insn, with the different OP_*
> codes encoded into the modrm byte.

I had to laugh when I read this; this is *exactly* what I had in mind,
but then I found out there was no ModR/M byte.

>> P.S. This is my first time using git send-email, so please bear with
>>      me if something goes wrong and/or let me know how I can improve
>>      my future submissions. Thank you!
> 
> You've done well with git send-email.  ;-)

Thanks a lot! :)

-Jan


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  reply	other threads:[~2019-04-12  1:43 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-08 18:27 [Qemu-devel] [RISU PATCH 0/5] Fix RISU build for i386 Jan Bobek
2019-04-08 18:27 ` Jan Bobek
2019-04-08 18:27 ` [Qemu-devel] [RISU PATCH 1/5] risu_i386: move reginfo_t and related defines to risu_reginfo_i386.h Jan Bobek
2019-04-08 18:27   ` Jan Bobek
2019-04-25 13:39   ` Alex Bennée
2019-04-25 13:39     ` Alex Bennée
2019-04-08 18:27 ` [Qemu-devel] [RISU PATCH 2/5] risu_i386: move reginfo-related code to risu_reginfo_i386.c Jan Bobek
2019-04-08 18:27   ` Jan Bobek
2019-04-25 13:39   ` Alex Bennée
2019-04-25 13:39     ` Alex Bennée
2019-04-08 18:27 ` [Qemu-devel] [RISU PATCH 3/5] risu_reginfo_i386: implement arch-specific reginfo interface Jan Bobek
2019-04-08 18:27   ` Jan Bobek
2019-04-25 13:42   ` Alex Bennée
2019-04-25 13:42     ` Alex Bennée
2019-04-08 18:27 ` [Qemu-devel] [RISU PATCH 4/5] risu_i386: implement missing CPU-specific functions Jan Bobek
2019-04-08 18:27   ` Jan Bobek
2019-04-08 18:27 ` [Qemu-devel] [RISU PATCH 5/5] risu_i386: remove old unused code Jan Bobek
2019-04-08 18:27   ` Jan Bobek
2019-04-25 13:43   ` Alex Bennée
2019-04-25 13:43     ` Alex Bennée
2019-04-08 22:18 ` [Qemu-devel] [RISU PATCH 0/5] Fix RISU build for i386 Richard Henderson
2019-04-08 22:18   ` Richard Henderson
2019-04-12  1:43   ` Jan Bobek [this message]
2019-04-12  1:43     ` Jan Bobek
2019-04-25 13:45 ` Alex Bennée
2019-04-25 13:45   ` Alex Bennée
2019-05-15 14:32   ` Jan Bobek

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