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[X86] Ignore REX prefixes not immediately before opcode #117299

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Merged
boomanaiden154 merged 2 commits into from
Nov 22, 2024
Merged

[X86] Ignore REX prefixes not immediately before opcode #117299

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[X86] Ignore REX prefixes not immediately before opcode
boomanaiden154 Nov 22, 2024
d14b59b
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boomanaiden154 Nov 22, 2024
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13 changes: 8 additions & 5 deletions llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -329,6 +329,14 @@ static int readPrefixes(struct InternalInstruction *insn) {
break;
}

if (isREX(insn, byte)) {
insn->rexPrefix = byte;
isPrefix = true;
LLVM_DEBUG(dbgs() << format("Found REX prefix 0x%hhx", byte));
} else if (isPrefix) {
insn->rexPrefix = 0;
}

if (isPrefix)
LLVM_DEBUG(dbgs() << format("Found prefix 0x%hhx", byte));
}
Expand Down Expand Up @@ -506,11 +514,6 @@ static int readPrefixes(struct InternalInstruction *insn) {
LLVM_DEBUG(dbgs() << format("Found REX2 prefix 0x%hhx 0x%hhx",
insn->rex2ExtensionPrefix[0],
insn->rex2ExtensionPrefix[1]));
} else if (isREX(insn, byte)) {
if (peek(insn, nextByte))
return -1;
insn->rexPrefix = byte;
LLVM_DEBUG(dbgs() << format("Found REX prefix 0x%hhx", byte));
} else
--insn->readerCursor;

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6 changes: 6 additions & 0 deletions llvm/test/MC/Disassembler/X86/x86-64.txt
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Expand Up @@ -770,3 +770,9 @@

# CHECK: prefetchit1 (%rip)
0x0f,0x18,0x35,0x00,0x00,0x00,0x00

# Check that we correctly ignore a REX prefix that is not immediately before
# the opcode. REX prefixes not immediately preceding the Opcode are ignored
# according to Section 2.2.1 of the Intel 64 Architecture Manual.
# CHECK: orw $25659, %ax
0x66 0x4c 0x64 0x0d 0x3b 0x64
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