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Refactor prefix decoder

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This commit is contained in:
Alexis Engelke
2019-01-13 15:54:47 +01:00
parent 4f4b2050c8
commit 5532602000
1 changed files with 56 additions and 154 deletions
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198
decode.c
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@@ -81,181 +81,83 @@ decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode,
while (LIKELY(off < len))
{
uint8_t prefix = buffer[off];
if (prefix == 0x2E)
switch (prefix)
{
prefixes |= PREFIX_SEG_CS;
}
else if (prefix == 0x26)
{
prefixes |= PREFIX_SEG_ES;
}
else if (prefix == 0x3E)
{
prefixes |= PREFIX_SEG_DS;
}
else if (prefix == 0x64)
{
prefixes |= PREFIX_SEG_FS;
}
else if (prefix == 0x65)
{
prefixes |= PREFIX_SEG_GS;
}
else if (prefix == 0x66)
{
prefixes |= PREFIX_OPSZ;
}
else if (prefix == 0x67)
{
prefixes |= PREFIX_ADDRSZ;
}
else if (prefix == 0xF0)
{
prefixes |= PREFIX_LOCK;
}
else if (prefix == 0xF2)
{
prefixes |= PREFIX_REPNZ;
}
else if (prefix == 0xF3)
{
prefixes |= PREFIX_REP;
}
default: goto out;
case 0x2e: prefixes |= PREFIX_SEG_CS; off++; break;
case 0x26: prefixes |= PREFIX_SEG_ES; off++; break;
case 0x3e: prefixes |= PREFIX_SEG_DS; off++; break;
case 0x64: prefixes |= PREFIX_SEG_FS; off++; break;
case 0x65: prefixes |= PREFIX_SEG_GS; off++; break;
case 0x66: prefixes |= PREFIX_OPSZ; off++; break;
case 0x67: prefixes |= PREFIX_ADDRSZ; off++; break;
case 0xf0: prefixes |= PREFIX_LOCK; off++; break;
case 0xf2: prefixes |= PREFIX_REPNZ; off++; break;
case 0xf3: prefixes |= PREFIX_REP; off++; break;
#if defined(ARCH_X86_64)
else if (mode == DECODE_64 && LIKELY(prefix >= 0x40 && prefix <= 0x4F))
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)
{
prefixes |= PREFIX_REX;
if (prefix & 0x1)
{
prefixes |= PREFIX_REXB;
}
if (prefix & 0x2)
{
prefixes |= PREFIX_REXX;
}
if (prefix & 0x4)
{
prefixes |= PREFIX_REXR;
}
if (prefix & 0x8)
{
prefixes |= PREFIX_REXW;
}
// REX prefix is the last prefix.
prefixes |= prefix & 0x1 ? PREFIX_REXB : 0;
prefixes |= prefix & 0x2 ? PREFIX_REXX : 0;
prefixes |= prefix & 0x4 ? PREFIX_REXR : 0;
prefixes |= prefix & 0x8 ? PREFIX_REXW : 0;
off++;
break;
}
// If in 64-bit mode, the REX prefix is always the last prefix. In
// 32-bit mode these are regular opcodes, so exit without consuming.
goto out;
#endif
else if (UNLIKELY(prefix == 0xc4))
{
// 3-byte VEX
if (UNLIKELY(off + 2 >= len))
{
case 0xc4: case 0xc5: // VEX
if (UNLIKELY(off + 1 >= len))
return -1;
}
#if defined(ARCH_386)
if (mode == DECODE_32 && (buffer[off + 1] & 0xc0) != 0xc0)
{
break;
}
#endif
uint8_t byte2 = buffer[off + 1];
uint8_t byte3 = buffer[off + 2];
uint8_t byte = buffer[off + 1];
if (mode == DECODE_32 && (byte & 0xc0) != 0xc0)
goto out;
prefixes |= PREFIX_VEX;
#if defined(ARCH_X86_64)
if (mode == DECODE_64 && (byte2 & 0x80) == 0)
prefixes |= byte & 0x80 ? 0 : PREFIX_REXR;
if (prefix == 0xc4) // 3-byte VEX
{
prefixes |= PREFIX_REXR;
}
if (mode == DECODE_64 && (byte2 & 0x40) == 0)
{
prefixes |= PREFIX_REXX;
}
if (mode == DECODE_64 && (byte2 & 0x20) == 0)
{
prefixes |= PREFIX_REXB;
}
#endif
switch (byte2 & 0x1f)
prefixes |= byte & 0x80 ? 0 : PREFIX_REXR;
prefixes |= byte & 0x40 ? 0 : PREFIX_REXX;
// SDM Vol 2A 2-15 (Dec. 2016): Ignored in 32-bit mode
prefixes |= mode == DECODE_64 || (byte & 0x20) ? 0 : PREFIX_REXB;
switch (byte & 0x1f)
{
case 0x01: prefixes |= PREFIX_ESC_0F; break;
case 0x02: prefixes |= PREFIX_ESC_0F38; break;
case 0x03: prefixes |= PREFIX_ESC_0F3A; break;
default: return -1;
}
if (byte3 & 0x04)
{
prefixes |= PREFIX_VEXL;
}
#if defined(ARCH_X86_64)
// Load third byte of VEX prefix
if (UNLIKELY(off + 2 >= len))
return -1;
byte = buffer[off + 2];
// SDM Vol 2A 2-16 (Dec. 2016)
// - "In 32-bit modes, VEX.W is silently ignored."
// - VEX.W either replaces REX.W, is don't care or is reserved.
if (mode == DECODE_64 && (byte3 & 0x80))
{
prefixes |= PREFIX_REXW;
}
#endif
*out_vex_operand = ((byte3 & 0x78) >> 3) ^ 0xf;
switch (byte3 & 0x03)
{
case 1: prefixes |= PREFIX_OPSZ; break;
case 2: prefixes |= PREFIX_REP; break;
case 3: prefixes |= PREFIX_REPNZ; break;
default: break;
}
// VEX prefix is always the last prefix.
off += 3;
break;
}
else if (UNLIKELY(prefix == 0xc5))
{
// 2-byte VEX
if (UNLIKELY(off + 1 >= len))
{
return -1;
}
#if defined(ARCH_386)
if (mode == DECODE_32 && (buffer[off + 1] & 0xc0) != 0xc0)
{
break;
}
#endif
uint8_t byte = buffer[off + 1];
prefixes |= PREFIX_VEX | PREFIX_ESC_0F;
#if defined(ARCH_X86_64)
if (mode == DECODE_64 && (byte & 0x80) == 0)
{
prefixes |= PREFIX_REXR;
}
#endif
if (byte & 0x04)
{
prefixes |= PREFIX_VEXL;
prefixes |= mode == DECODE_64 && (byte & 0x80) ? PREFIX_REXW : 0;
}
else // 2-byte VEX
prefixes |= PREFIX_ESC_0F;
prefixes |= byte & 0x04 ? PREFIX_VEXL : 0;
prefixes |= (byte & 0x03) == 1 ? PREFIX_OPSZ : 0;
prefixes |= (byte & 0x03) == 2 ? PREFIX_REP : 0;
prefixes |= (byte & 0x03) == 3 ? PREFIX_REPNZ : 0;
*out_vex_operand = ((byte & 0x78) >> 3) ^ 0xf;
switch (byte & 0x03)
{
case 1: prefixes |= PREFIX_OPSZ; break;
case 2: prefixes |= PREFIX_REP; break;
case 3: prefixes |= PREFIX_REPNZ; break;
default: break;
}
// VEX prefix is always the last prefix.
off += 2;
break;
off += prefix == 0xc4 ? 3 : 2;
goto out;
}
else
{
break;
}
off++;
}
out:
if (out_prefixes != NULL)
{
*out_prefixes = prefixes;