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From: "boudewijn83 at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug breakpoints/31481] Certain instructions load the wrong
 RIP-relative memory after setting a breakpoint
Date: Sat, 16 Mar 2024 11:54:15 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31481

--- Comment #4 from Boudewijn <boudewijn83 at gmail dot com> ---
Created attachment 15409
  --> https://sourceware.org/bugzilla/attachment.cgi?id=3D15409&action=3Ded=
it
Proposed patch, fixes #28999 and #31481

There's actually no need for an extra lookup table.

All (E)VEX prefixed instructions share the same two properties:

- the (explicit part of the) opcode is only 1 byte
- they all have a ModRM byte, except VZEROALL/VZEROUPPER

So when there's an (E)VEX prefix it suffices to test for VZEROALL/VZEROUPPER
(opcode 0x77):

  if (vex2 or vex3 or evex) {
    details->opcode_len =3D 1;
    need_modrm =3D (*insn !=3D 0x77);
  } else {
    use the legacy has_modrm tables
  }

I've attached a patch that implements this.

PS: I've tested VEX2/VEX3, but don't have an AVX-512 capable CPU so I'm not
able to test the EVEX handling.

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