Re: Inconsistent usage on onebyte_modrm and twobyte_modrm table in x86 disassembler and gdb?

[Tom de Vries <tdevries@suse.de>]

On 8/26/25 10:19, Gerlicher, Klaus wrote:
> FWIW I'll attach my fix for the (V)PBLENDW. It has a testcase and a unittest case.

Hi Klaus,

thanks for working on this.

The patch LGTM, other than this:
...
$ git show --pretty=%s --check
Fix vpblendw

gdb/amd64-tdep.c:1409: space before tab in indent.
+      	  need_modrm = 1;
...

I've tested both the unit test, and the updated test-case.

I've also tested the unit test I wrote, which uses vex3 instead of evex:
...
+
+  /* INSN: vpblendw $0x7,%xmm4,%xmm6,%xmm2, vex3 prefix.  */
+  insn = { 0xc4, 0xe3, 0x49, 0x0e, 0xd4, 0x07 };
+  amd64_get_insn_details (insn.data (), &details);
+  SELF_CHECK (details.opcode_len == 3);
+  SELF_CHECK (details.enc_prefix_offset == 0);
+  SELF_CHECK (details.opcode_offset == 3);
+  SELF_CHECK (details.modrm_offset == 4);
+
+  /* INSN: vpblendw $0x7,0xff(%rip),%ymm6,%ymm2, vex3 prefix.  */
+  insn = { 0xc4, 0xe3, 0x4d, 0x0e, 0x15, 0xff, 0x00, 0x00, 0x00, 0x07 };
+  amd64_get_insn_details (insn.data (), &details);
+  SELF_CHECK (details.opcode_len == 3);
+  SELF_CHECK (details.enc_prefix_offset == 0);
+  SELF_CHECK (details.opcode_offset == 3);
+  SELF_CHECK (details.modrm_offset == 4);
+
+  /* INSN: vpblendw $0x7,0xff(%ecx),%ymm6,%ymm2, vex3 prefix.  */
+  fixup_riprel (details, insn.data (), ECX_REG_NUM);
+  updated_insn
+    = { 0xc4, 0xe3, 0x4d, 0x0e, 0x91, 0xff, 0x00, 0x00, 0x00, 0x07 };
+  SELF_CHECK (insn == updated_insn);
...

You could add this as well, but it's not required.

[ Note that you could drop the test-case update and use fixup_riprel on 
the unit test you added instead, like I did here and is done elsewhere 
in the unit test. ]

Please commit this with some appropriate $subject.

Approved-By: Tom de Vries <tdevries@suse.de>

Thanks,
- Tom