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Re: [Qemu-devel] [RISU PATCH 0/5] Fix RISU build for i386
From: |
Jan Bobek |
Subject: |
Re: [Qemu-devel] [RISU PATCH 0/5] Fix RISU build for i386 |
Date: |
Thu, 11 Apr 2019 21:43:37 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 |
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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- [Qemu-devel] [RISU PATCH 1/5] risu_i386: move reginfo_t and related defines to risu_reginfo_i386.h, (continued)
- [Qemu-devel] [RISU PATCH 1/5] risu_i386: move reginfo_t and related defines to risu_reginfo_i386.h, Jan Bobek, 2019/04/08
- [Qemu-devel] [RISU PATCH 3/5] risu_reginfo_i386: implement arch-specific reginfo interface, Jan Bobek, 2019/04/08
- [Qemu-devel] [RISU PATCH 5/5] risu_i386: remove old unused code, Jan Bobek, 2019/04/08
- [Qemu-devel] [RISU PATCH 2/5] risu_i386: move reginfo-related code to risu_reginfo_i386.c, Jan Bobek, 2019/04/08
- [Qemu-devel] [RISU PATCH 4/5] risu_i386: implement missing CPU-specific functions, Jan Bobek, 2019/04/08
- Re: [Qemu-devel] [RISU PATCH 0/5] Fix RISU build for i386, Richard Henderson, 2019/04/08
- Re: [Qemu-devel] [RISU PATCH 0/5] Fix RISU build for i386,
Jan Bobek <=
- Re: [Qemu-devel] [RISU PATCH 0/5] Fix RISU build for i386, Alex Bennée, 2019/04/25