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[X86][Disassembler] Simplify readPrefixes

This commit is contained in:
Fangrui Song 2020-01-10 23:31:49 -08:00
parent 69806808b9
commit fcad5b298c
1 changed files with 26 additions and 44 deletions
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70
llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
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@ -289,43 +289,6 @@ static bool isREX(struct InternalInstruction *insn, uint8_t prefix) {
return false;
}
/*
* setPrefixPresent - Marks that a particular prefix is present as mandatory
*
* @param insn - The instruction to be marked as having the prefix.
* @param prefix - The prefix that is present.
*/
static void setPrefixPresent(struct InternalInstruction *insn, uint8_t prefix) {
uint8_t nextByte;
switch (prefix) {
case 0xf0:
insn->hasLockPrefix = true;
break;
case 0xf2:
case 0xf3:
if (lookAtByte(insn, &nextByte))
break;
// TODO:
// 1. There could be several 0x66
// 2. if (nextByte == 0x66) and nextNextByte != 0x0f then
// it's not mandatory prefix
// 3. if (nextByte >= 0x40 && nextByte <= 0x4f) it's REX and we need
// 0x0f exactly after it to be mandatory prefix
if (isREX(insn, nextByte) || nextByte == 0x0f || nextByte == 0x66)
// The last of 0xf2 /0xf3 is mandatory prefix
insn->mandatoryPrefix = prefix;
insn->repeatPrefix = prefix;
break;
case 0x66:
if (lookAtByte(insn, &nextByte))
break;
// 0x66 can't overwrite existing mandatory prefix and should be ignored
if (!insn->mandatoryPrefix && (nextByte == 0x0f || isREX(insn, nextByte)))
insn->mandatoryPrefix = prefix;
break;
}
}
/*
* readPrefixes - Consumes all of an instruction's prefix bytes, and marks the
* instruction as having them. Also sets the instruction's default operand,
@ -393,10 +356,25 @@ static int readPrefixes(struct InternalInstruction* insn) {
switch (byte) {
case 0xf0: /* LOCK */
case 0xf2: /* REPNE/REPNZ */
case 0xf3: /* REP or REPE/REPZ */
setPrefixPresent(insn, byte);
insn->hasLockPrefix = true;
break;
case 0xf2: /* REPNE/REPNZ */
case 0xf3: /* REP or REPE/REPZ */ {
uint8_t nextByte;
if (lookAtByte(insn, &nextByte))
break;
// TODO:
// 1. There could be several 0x66
// 2. if (nextByte == 0x66) and nextNextByte != 0x0f then
// it's not mandatory prefix
// 3. if (nextByte >= 0x40 && nextByte <= 0x4f) it's REX and we need
// 0x0f exactly after it to be mandatory prefix
if (isREX(insn, nextByte) || nextByte == 0x0f || nextByte == 0x66)
// The last of 0xf2 /0xf3 is mandatory prefix
insn->mandatoryPrefix = byte;
insn->repeatPrefix = byte;
break;
}
case 0x2e: /* CS segment override -OR- Branch not taken */
case 0x36: /* SS segment override -OR- Branch taken */
case 0x3e: /* DS segment override */
@ -426,15 +404,19 @@ static int readPrefixes(struct InternalInstruction* insn) {
debug("Unhandled override");
return -1;
}
setPrefixPresent(insn, byte);
break;
case 0x66: /* Operand-size override */
case 0x66: /* Operand-size override */ {
uint8_t nextByte;
insn->hasOpSize = true;
setPrefixPresent(insn, byte);
if (lookAtByte(insn, &nextByte))
break;
// 0x66 can't overwrite existing mandatory prefix and should be ignored
if (!insn->mandatoryPrefix && (nextByte == 0x0f || isREX(insn, nextByte)))
insn->mandatoryPrefix = byte;
break;
}
case 0x67: /* Address-size override */
insn->hasAdSize = true;
setPrefixPresent(insn, byte);
break;
default: /* Not a prefix byte */
isPrefix = false;