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decode: Ignore ES/CS/SS/DS override in 64-bit mode

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Alexis Engelke
2020-11-22 20:59:13 +01:00
parent 8ab9f641b8
commit bb8510d77f
2 changed files with 65 additions and 38 deletions
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81
decode.c
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@@ -238,39 +238,60 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
int rex_off = -1;
instr->segment = FD_REG_NONE;
while (LIKELY(off < len))
{
uint8_t prefix = buffer[off];
switch (UNLIKELY(prefix))
#if defined(ARCH_386)
if (mode == DECODE_32) {
while (LIKELY(off < len))
{
default: goto prefix_end;
// From segment overrides, the last one wins.
case 0x26: instr->segment = FD_REG_ES; break;
case 0x2e: instr->segment = FD_REG_CS; break;
case 0x36: instr->segment = FD_REG_SS; break;
case 0x3e: instr->segment = FD_REG_DS; break;
case 0x64: instr->segment = FD_REG_FS; break;
case 0x65: instr->segment = FD_REG_GS; break;
case 0x66: prefix_66 = true; break;
case 0x67: prefix_67 = true; break;
case 0xf0: prefix_lock = true; break;
// From REP/REPE and REPNZ, the last one wins; and for mandatory
// prefixes they have a higher priority than 66h (handled below).
case 0xf3: prefix_rep = 2; break;
case 0xf2: prefix_rep = 3; break;
#if defined(ARCH_X86_64)
case 0x40: case 0x41: case 0x42: case 0x43: case 0x44: case 0x45:
case 0x46: case 0x47: case 0x48: case 0x49: case 0x4a: case 0x4b:
case 0x4c: case 0x4d: case 0x4e: case 0x4f:
if (mode != DECODE_64)
goto prefix_end;
prefix_rex = prefix;
rex_off = off;
break;
#endif
uint8_t prefix = buffer[off];
switch (UNLIKELY(prefix))
{
default: goto prefix_end;
// From segment overrides, the last one wins.
case 0x26: instr->segment = FD_REG_ES; break;
case 0x2e: instr->segment = FD_REG_CS; break;
case 0x36: instr->segment = FD_REG_SS; break;
case 0x3e: instr->segment = FD_REG_DS; break;
case 0x64: instr->segment = FD_REG_FS; break;
case 0x65: instr->segment = FD_REG_GS; break;
case 0x66: prefix_66 = true; break;
case 0x67: prefix_67 = true; break;
case 0xf0: prefix_lock = true; break;
case 0xf3: prefix_rep = 2; break;
case 0xf2: prefix_rep = 3; break;
}
off++;
}
off++;
}
#endif
#if defined(ARCH_X86_64)
if (mode == DECODE_64) {
while (LIKELY(off < len))
{
uint8_t prefix = buffer[off];
switch (UNLIKELY(prefix))
{
default: goto prefix_end;
// ES/CS/SS/DS overrides are ignored.
case 0x26: case 0x2e: case 0x36: case 0x3e: break;
// From segment overrides, the last one wins.
case 0x64: instr->segment = FD_REG_FS; break;
case 0x65: instr->segment = FD_REG_GS; break;
case 0x66: prefix_66 = true; break;
case 0x67: prefix_67 = true; break;
case 0xf0: prefix_lock = true; break;
case 0xf3: prefix_rep = 2; break;
case 0xf2: prefix_rep = 3; break;
case 0x40: case 0x41: case 0x42: case 0x43: case 0x44: case 0x45:
case 0x46: case 0x47: case 0x48: case 0x49: case 0x4a: case 0x4b:
case 0x4c: case 0x4d: case 0x4e: case 0x4f:
prefix_rex = prefix;
rex_off = off;
break;
}
off++;
}
}
#endif
prefix_end:
// REX prefix is only considered if it is the last prefix.