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ljkxandClaude Opus 5.5
d54dfb1595
In 64-bit mode a REX prefix only takes effect when it immediately precedes the opcode; a REX followed by a legacy prefix or another REX is ignored. The instruction decoder, the rewriter's reference classifier, DecodedInstruction and the SSE4a, SHA-256 and CLZERO operand decoders read legacy prefixes and then at most one REX. `48 F3 0F 2B 00` (MOVNTSS) was therefore scanned as `[48 F3][0F 2B 00]` and kept, and `48 67 0F 01 FC` lost its address-size prefix. All of them now accept REX bytes among the prefixes and keep only one that directly precedes the opcode. The converter's guard against prefix-only fragments is removed, since the decoder no longer produces them, and the TechnicalDebt entry describing the split is dropped. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
54 lines
1.5 KiB
C++
54 lines
1.5 KiB
C++
#include <codegen/x86/ClzeroOperands.hpp>
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#include <codegen/x86/X64OpcodeConstants.hpp>
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#include <codegen/CodegenException.hpp>
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namespace Codegen {
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using namespace X64OpcodeConstants;
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namespace {
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constexpr std::size_t kMaxInstructionLength = 15;
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}
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ClzeroOperands DecodeClzero(const std::uint8_t* data, const std::size_t length) {
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if (length > kMaxInstructionLength) {
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throw CodegenException("CLZERO longer than 15 bytes");
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}
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ClzeroOperands operands{};
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std::size_t pos = 0;
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while (pos < length) {
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const std::uint8_t b = data[pos];
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if (b >= RexMin && b <= RexMax) {
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pos += 1;
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continue;
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}
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if (b == PrefixLock) {
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throw CodegenException("CLZERO with a LOCK prefix");
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}
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if (b == PrefixSegFs || b == PrefixSegGs) {
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throw CodegenException("CLZERO with an FS or GS segment override");
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}
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if (b == PrefixOperandSize || b == PrefixRepne || b == PrefixRep) {
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throw CodegenException("Not a CLZERO instruction");
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}
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if (b == PrefixAddressSize) {
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operands.AddressSize32 = true;
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} else if (b != PrefixSegCs && b != PrefixSegSs && b != PrefixSegDs && b != PrefixSegEs) {
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break;
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}
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pos += 1;
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}
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if (pos + 3 != length || data[pos] != TwoByteOpcodeEscape || data[pos + 1] != TwoByteGrp7 || data[pos + 2] != 0xFC) {
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throw CodegenException("Not a CLZERO instruction");
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}
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return operands;
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}
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}
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