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Re: [PATCH 2/6] x86-64: Intel64 adjustments for conditional jumps
On 06.03.2020 15:39, H.J. Lu wrote:
> On Fri, Mar 6, 2020 at 12:12 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> Just like for unconditional direct JMP, AMD and Intel differ in their
>> handling. Mirror JMP handling to Jcc.
>>
>> gas/
>> 2020-03-XX Jan Beulich <jbeulich@suse.com>
>>
>> * testsuite/gas/i386/x86-64-branch-2.s,
>> testsuite/gas/i386/x86-64-branch-3.s: Add Jcc cases.
>> * testsuite/gas/i386/ilp32/x86-64-branch.d,
>> testsuite/gas/i386/opcode-suffix.d,
>> testsuite/gas/i386/x86-64-branch-2.d,
>> testsuite/gas/i386/x86-64-branch-3.d,
>> testsuite/gas/i386/x86-64-branch.d: Adjust expectations.
>>
>> opcodes/
>> 2020-03-XX Jan Beulich <jbeulich@suse.com>
>>
>> * i386-dis.c (safe-ctype.h): Include.
>> (X86_64_0F8x): New enumerator.
>> (dis386): Extend comment ahead of it.
>> (dis386_twobyte): Vector Jcc to X86_64_0F8x.
>> (condition_code): New.
>> (x86_64_table): Add X86_64_0F8x entry.
>> (print_insn): Set condition_code. Move advancing of codep after
>> it.
>> (putop): Handle two-char escape case for 'C'. Handle 'C' prefix
>> case for 'P' and '@'.
>> * i386-opc.tbl (j<cc>): Split into AMD64 and Intel64 variants.
>> * i386-tbl.h: Re-generate.
>> ---
>> I wonder if the suffix handling done here wouldn't also be the more
>> suitable one for JMP and CALL. In particular the 'q' suffix printed
>> unconditionally in 64-bit mode is more of a problem than helpful imo.
>>
>> --- a/gas/testsuite/gas/i386/ilp32/x86-64-branch.d
>> +++ b/gas/testsuite/gas/i386/ilp32/x86-64-branch.d
>> @@ -22,7 +22,7 @@ Disassembly of section .text:
>> [ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 0x24 20: R_X86_64_PC32 \*ABS\*\+0x10003c
>> [ ]*[a-f0-9]+: 66 e8 00 00 00 00 data16 callq 0x2a 26: R_X86_64_PLT32 foo-0x4
>> [ ]*[a-f0-9]+: 66 e9 00 00 00 00 data16 jmpq 0x30 2c: R_X86_64_PLT32 foo-0x4
>> -[ ]*[a-f0-9]+: 66 0f 82 00 00 00 00 data16 jb 0x37 33: R_X86_64_PLT32 foo-0x4
>> +[ ]*[a-f0-9]+: 66 0f 82 00 00 00 00 data16 jbq 0x37 33: R_X86_64_PLT32 foo-0x4
>> [ ]*[a-f0-9]+: 66 c3 data16 retq *
>> [ ]*[a-f0-9]+: 66 c2 08 00 data16 retq \$0x8
>> [ ]*[a-f0-9]+: ff d0 callq \*%rax
>
> I think it is a very bad idea to add suffix to jcc.
Well, do you have an alternative suggestion, also in line with
JMP then? (See the somewhat related post-commit-message remark
above as well.) I'd like to note that a suffix gets put there
_only_ if there's also a data16 prefix (to be able to tell
apart the different cases).
Jan