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decode: Handle imm_byte size differently

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For byte-sized immediates, there are only two options for the operand
size: byte and the instruction's operand size. This knowledge allows to
remove the byte constraint from the set of fixed operand sizes.
This commit is contained in:
Alexis Engelke
2022-12-27 19:42:40 +01:00
parent 1aec30cd0f
commit 377e362a0e
2 changed files with 52 additions and 41 deletions
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72
decode.c
View File

@@ -494,47 +494,51 @@ skip_modrm:
}
else if (imm_control != 0)
{
FdOp* operand = &instr->operands[DESC_IMM_IDX(desc)];
operand->type = FD_OT_IMM;
operand->size = operand_sizes[(desc->operand_sizes >> 6) & 3];
// 4/5 = immediate, operand-sized/8 bit
// 6/7 = offset, operand-sized/8 bit (used for jumps/calls)
int imm_byte = imm_control & 1;
int imm_offset = imm_control & 2;
uint8_t imm_size;
if (imm_byte)
imm_size = 1;
else if (UNLIKELY(instr->type == FDI_RET || instr->type == FDI_RETF ||
instr->type == FDI_SSE_EXTRQ ||
instr->type == FDI_SSE_INSERTQ))
imm_size = 2;
else if (UNLIKELY(instr->type == FDI_JMPF || instr->type == FDI_CALLF))
imm_size = (1 << op_size >> 1) + 2;
else if (UNLIKELY(instr->type == FDI_ENTER))
imm_size = 3;
else if (instr->type == FDI_MOVABS)
imm_size = (1 << op_size >> 1);
else
imm_size = op_size == 2 ? 2 : 4;
FdOp* operand = &instr->operands[DESC_IMM_IDX(desc)];
operand->type = FD_OT_IMM;
if (UNLIKELY(off + imm_size > len))
return FD_ERR_PARTIAL;
if (imm_byte) {
if (UNLIKELY(off + 1 > len))
return FD_ERR_PARTIAL;
instr->imm = (int8_t) LOAD_LE_1(&buffer[off++]);
operand->size = desc->operand_sizes & 0x40 ? 1 : op_size;
} else {
operand->size = operand_sizes[(desc->operand_sizes >> 6) & 3];
if (imm_size == 1)
instr->imm = (int8_t) LOAD_LE_1(&buffer[off]);
else if (imm_size == 2)
instr->imm = (int16_t) LOAD_LE_2(&buffer[off]);
else if (imm_size == 3)
instr->imm = LOAD_LE_3(&buffer[off]);
else if (imm_size == 4)
instr->imm = (int32_t) LOAD_LE_4(&buffer[off]);
else if (imm_size == 6)
instr->imm = LOAD_LE_4(&buffer[off]) | LOAD_LE_2(&buffer[off+4]) << 32;
else if (imm_size == 8)
instr->imm = (int64_t) LOAD_LE_8(&buffer[off]);
off += imm_size;
uint8_t imm_size;
if (UNLIKELY(instr->type == FDI_RET || instr->type == FDI_RETF ||
instr->type == FDI_SSE_EXTRQ ||
instr->type == FDI_SSE_INSERTQ))
imm_size = 2;
else if (UNLIKELY(instr->type == FDI_JMPF || instr->type == FDI_CALLF))
imm_size = (1 << op_size >> 1) + 2;
else if (UNLIKELY(instr->type == FDI_ENTER))
imm_size = 3;
else if (instr->type == FDI_MOVABS)
imm_size = (1 << op_size >> 1);
else
imm_size = op_size == 2 ? 2 : 4;
if (UNLIKELY(off + imm_size > len))
return FD_ERR_PARTIAL;
if (imm_size == 2)
instr->imm = (int16_t) LOAD_LE_2(&buffer[off]);
else if (imm_size == 3)
instr->imm = LOAD_LE_3(&buffer[off]);
else if (imm_size == 4)
instr->imm = (int32_t) LOAD_LE_4(&buffer[off]);
else if (imm_size == 6)
instr->imm = LOAD_LE_4(&buffer[off]) | LOAD_LE_2(&buffer[off+4]) << 32;
else if (imm_size == 8)
instr->imm = (int64_t) LOAD_LE_8(&buffer[off]);
off += imm_size;
}
if (imm_offset)
{

21
parseinstrs.py
View File

@@ -269,8 +269,13 @@ class InstrDesc(NamedTuple):
extraflags["instr_width"] = "INSTR_WIDTH" in self.flags
extraflags["lock"] = "LOCK" in self.flags
imm_byte = self.imm_size(4) == 1
extraflags["imm_control"] = flags.imm_control | imm_byte
# Sort fixed sizes encodable in size_fix2 as second element.
fixed = set(self.OPKIND_SIZES[op.size] for op in self.operands if op.size >= 0)
# But: byte-sized immediates are handled specially and don't cost space.
fixed = set(self.OPKIND_SIZES[op.size] for op in self.operands if
op.size >= 0 and not (imm_byte and op.kind == "IMM"))
fixed = sorted(fixed, key=lambda x: 1 <= x <= 4)
if len(fixed) > 2 or (len(fixed) == 2 and not (1 <= fixed[1] <= 4)):
raise Exception(f"invalid fixed sizes {fixed} in {self}")
@@ -280,9 +285,14 @@ class InstrDesc(NamedTuple):
for i, opkind in enumerate(self.operands):
sz = self.OPKIND_SIZES[opkind.size] if opkind.size >= 0 else opkind.size
opname = ENCODING_OPORDER[self.encoding][i]
extraflags[f"{opname}_size"] = sizes.index(sz)
extraflags[f"{opname}_ty"] = self.OPKIND_REGTYS[opname, opkind.kind]
if opkind.kind == "IMM":
if imm_byte and sz not in (dynsizes[0], 1):
raise Exception(f"imm_byte with opsize {sz} in {self}")
extraflags[f"imm_size"] = sz == 1 if imm_byte else sizes.index(sz)
else:
opname = ENCODING_OPORDER[self.encoding][i]
extraflags[f"{opname}_size"] = sizes.index(sz)
extraflags[f"{opname}_ty"] = self.OPKIND_REGTYS[opname, opkind.kind]
# Miscellaneous Flags
if "VSIB" in self.flags: extraflags["vsib"] = 1
@@ -291,9 +301,6 @@ class InstrDesc(NamedTuple):
if "U66" not in self.flags and (ign66 or "I66" in self.flags):
extraflags["ign66"] = 1
if self.imm_size(4) == 1:
extraflags["imm_control"] = flags.imm_control | 1
enc = flags._replace(**extraflags)._encode()
enc = tuple((enc >> i) & 0xffff for i in range(0, 48, 16))
# First 2 bytes are the mnemonic, last 6 bytes are the encoding.