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decode: Minor refactoring for better performance

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This improves decoding performance by ~4%.
This commit is contained in:
Alexis Engelke
2020-06-19 09:41:26 +02:00
parent bb4b195dbe
commit 348d1aec4b
1 changed files with 28 additions and 33 deletions
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59
decode.c
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@@ -206,7 +206,7 @@ decode_modrm(const uint8_t* buffer, int len, DecodeMode mode, FdInstr* instr,
uint8_t rm = modrm & 0x07;
// VSIB must have a memory operand with SIB byte.
if (vsib && (rm != 4 || mod == 3))
if (UNLIKELY(vsib) && (rm != 4 || mod == 3))
return FD_ERR_UD;
// Operand 2 may be NULL when reg field is used as opcode extension
@@ -354,7 +354,9 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
{
// "Legacy" walk through table and escape opcodes
ENTRY_UNPACK(table, kind, table[0]);
while (kind == ENTRY_TABLE256 && LIKELY(off < len))
if (kind == ENTRY_TABLE256 && LIKELY(off < len))
ENTRY_UNPACK(table, kind, table[buffer[off++]]);
if (UNLIKELY(kind == ENTRY_TABLE256) && LIKELY(off < len))
ENTRY_UNPACK(table, kind, table[buffer[off++]]);
}
else
@@ -386,8 +388,7 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
prefixes &= ~(PREFIX_OPSZ | PREFIX_REPNZ | PREFIX_REP);
ENTRY_UNPACK(table, kind, table[mandatory_prefix]);
}
if (kind == ENTRY_TABLE_PREFIX_REP)
else if (kind == ENTRY_TABLE_PREFIX_REP)
{
// Discard 66h mandatory prefix
uint8_t index = mandatory_prefix != 1 ? mandatory_prefix : 0;
@@ -427,8 +428,7 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
op_size = 8;
else
op_size = 4;
instr->operandsz = desc->gp_instr_width ? op_size : 0;
// Note: operand size is updates for jumps when handling immediate operands.
uint8_t vec_size = 16;
if (prefixes & PREFIX_VEXL)
@@ -436,20 +436,11 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
// Compute address size.
uint8_t addr_size = mode == DECODE_64 ? 8 : 4;
if (prefixes & PREFIX_ADDRSZ)
if (UNLIKELY(prefixes & PREFIX_ADDRSZ))
addr_size >>= 1;
instr->addrsz = addr_size;
uint8_t operand_sizes[4] = {
0, 1 << desc->gp_fixed_operand_size, op_size, vec_size
};
__builtin_memset(instr->operands, 0, sizeof(instr->operands));
for (int i = 0; i < 4; i++)
{
uint8_t enc_size = (desc->operand_sizes >> 2 * i) & 3;
instr->operands[i].size = operand_sizes[enc_size];
}
if (DESC_HAS_IMPLICIT(desc))
{
@@ -552,6 +543,10 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
// 6/7 = offset, operand-sized/8 bit (used for jumps/calls)
int imm_byte = imm_control & 1;
int imm_offset = imm_control & 2;
// Jumps are always 8 or 32 bit on x86-64, and the operand size is
// forced to 64 bit.
if (mode == DECODE_64 && UNLIKELY(imm_offset))
op_size = 8;
uint8_t imm_size;
if (imm_byte)
@@ -560,11 +555,6 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
imm_size = 2;
else if (UNLIKELY(instr->type == FDI_ENTER))
imm_size = 3;
#if defined(ARCH_X86_64)
else if (mode == DECODE_64 && UNLIKELY(imm_offset))
// Jumps are always 8 or 32 bit on x86-64.
imm_size = 4;
#endif
else if (op_size == 2)
imm_size = 2;
#if defined(ARCH_X86_64)
@@ -598,11 +588,6 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
instr->imm += instr->address + off;
else
operand->type = FD_OT_OFF;
#if defined(ARCH_X86_64)
// On x86-64, jumps always have an operand size of 64 bit.
if (mode == DECODE_64)
operand->size = 8;
#endif
}
}
@@ -621,13 +606,22 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
}
}
if ((prefixes & PREFIX_LOCK) && !desc->lock)
return FD_ERR_UD;
if ((prefixes & PREFIX_LOCK) && instr->operands[0].type != FD_OT_MEM)
if (UNLIKELY(prefixes & PREFIX_LOCK))
if (!desc->lock || instr->operands[0].type != FD_OT_MEM)
return FD_ERR_UD;
uint8_t operand_sizes[4] = {
0, 1 << desc->gp_fixed_operand_size, op_size, vec_size
};
for (int i = 0; i < 4; i++)
{
if (instr->operands[i].type == FD_OT_NONE)
break;
uint8_t enc_size = (desc->operand_sizes >> 2 * i) & 3;
instr->operands[i].size = operand_sizes[enc_size];
uint32_t reg_type = (desc->reg_types >> 4 * i) & 0xf;
uint32_t reg_idx = instr->operands[i].reg;
if (reg_type == FD_RT_MEM && instr->operands[i].type != FD_OT_MEM)
@@ -641,14 +635,14 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
if ((reg_type == FD_RT_MMX || reg_type == FD_RT_SEG) && reg_idx >= 8)
instr->operands[i].reg -= 8;
// Reject invalid segment registers
if (reg_type == FD_RT_SEG && reg_idx >= 6)
if (UNLIKELY(reg_type == FD_RT_SEG) && reg_idx >= 6)
return FD_ERR_UD;
// Reject invalid control registers
if (reg_type == FD_RT_CR && reg_idx != 0 && reg_idx != 2 &&
if (UNLIKELY(reg_type == FD_RT_CR) && reg_idx != 0 && reg_idx != 2 &&
reg_idx != 3 && reg_idx != 4 && reg_idx != 8)
return FD_ERR_UD;
// Reject invalid debug registers
if (reg_type == FD_RT_DR && reg_idx >= 8)
if (UNLIKELY(reg_type == FD_RT_DR) && reg_idx >= 8)
return FD_ERR_UD;
instr->operands[i].misc = reg_type;
}
@@ -657,6 +651,7 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
return FD_ERR_UD;
instr->size = off;
instr->operandsz = desc->gp_instr_width ? op_size : 0;
return off;
}