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decode: Remove PrefixSet enum

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This commit is contained in:
Alexis Engelke
2020-11-22 16:02:35 +01:00
parent ad1f1e39c3
commit f4215d4260
1 changed files with 86 additions and 122 deletions
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208
decode.c
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@@ -50,98 +50,20 @@ table_walk(unsigned cur_idx, unsigned entry_idx, unsigned* out_kind) {
#define LOAD_LE_4(buf) (LOAD_LE_2(buf) | LOAD_LE_2((uint8_t*) (buf) + 2)<<16)
#define LOAD_LE_8(buf) (LOAD_LE_4(buf) | LOAD_LE_4((uint8_t*) (buf) + 4)<<32)
enum PrefixSet
enum
{
PREFIX_LOCK = FD_FLAG_LOCK,
PREFIX_REP = FD_FLAG_REP,
PREFIX_REPNZ = FD_FLAG_REPNZ,
PREFIX_REX = 1 << 8,
PREFIX_OPSZ = 1 << 13,
PREFIX_ADDRSZ = 1 << 14,
PREFIX_REXB = 1 << 15,
PREFIX_REXX = 1 << 16,
PREFIX_REXR = 1 << 17,
PREFIX_REXW = 1 << 18,
PREFIX_VEXL = 1 << 19,
PREFIX_REXB = 0x01,
PREFIX_REXX = 0x02,
PREFIX_REXR = 0x04,
PREFIX_REXW = 0x08,
PREFIX_REX = 0x40,
PREFIX_VEXL = 0x10,
};
typedef enum PrefixSet PrefixSet;
static
int
decode_prefixes(const uint8_t* buffer, int len, DecodeMode mode,
PrefixSet* out_prefixes, uint8_t* out_mandatory,
uint8_t* out_segment)
{
int off = 0;
PrefixSet prefixes = 0;
PrefixSet rex_prefix = 0;
int rex_off = -1;
uint8_t rep = 0;
*out_mandatory = 0;
*out_segment = FD_REG_NONE;
while (LIKELY(off < len))
{
uint8_t prefix = buffer[off];
switch (UNLIKELY(prefix))
{
default: goto out;
// From segment overrides, the last one wins.
case 0x26: *out_segment = FD_REG_ES; break;
case 0x2e: *out_segment = FD_REG_CS; break;
case 0x36: *out_segment = FD_REG_SS; break;
case 0x3e: *out_segment = FD_REG_DS; break;
case 0x64: *out_segment = FD_REG_FS; break;
case 0x65: *out_segment = FD_REG_GS; break;
case 0x67: prefixes |= PREFIX_ADDRSZ; break;
case 0xf0: prefixes |= PREFIX_LOCK; break;
case 0x66: prefixes |= PREFIX_OPSZ; 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: rep = 2; break;
case 0xf2: 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 out;
rex_prefix = PREFIX_REX;
rex_prefix |= prefix & 0x1 ? PREFIX_REXB : 0;
rex_prefix |= prefix & 0x2 ? PREFIX_REXX : 0;
rex_prefix |= prefix & 0x4 ? PREFIX_REXR : 0;
rex_prefix |= prefix & 0x8 ? PREFIX_REXW : 0;
rex_off = off;
break;
#endif
}
off++;
}
out:
// REX prefix is only considered if it is the last prefix.
if (rex_off == off - 1)
prefixes |= rex_prefix;
// If there is no REP/REPNZ prefix and implied opcode extension from a VEX
// prefix, offer 66h as mandatory prefix. If there is a REP prefix, then the
// 66h prefix is ignored when evaluating mandatory prefixes.
if (rep) {
*out_mandatory = rep;
prefixes |= rep == 3 ? PREFIX_REPNZ : PREFIX_REP;
} else if (prefixes & PREFIX_OPSZ)
*out_mandatory = 1;
*out_prefixes = prefixes;
return off;
}
static
int
decode_modrm(const uint8_t* buffer, int len, DecodeMode mode, FdInstr* instr,
PrefixSet prefixes, bool vsib, FdOp* out_o1, FdOp* out_o2)
unsigned prefixes, bool vsib, FdOp* out_o1, FdOp* out_o2)
{
int off = 0;
@@ -305,21 +227,60 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
default: return FD_ERR_INTERNAL;
}
int retval;
int off = 0;
uint8_t vex_operand = 0;
uint8_t mandatory_prefix;
int opcode_escape = 0;
PrefixSet prefixes = 0;
retval = decode_prefixes(buffer + off, len - off, mode, &prefixes,
&mandatory_prefix, &instr->segment);
if (UNLIKELY(retval < 0))
return retval;
if (UNLIKELY(off + retval >= len))
unsigned prefix_rep = 0;
bool prefix_lock = false;
bool prefix_66 = false;
bool prefix_67 = false;
unsigned prefix_rex = 0;
int rex_off = -1;
instr->segment = FD_REG_NONE;
while (LIKELY(off < len))
{
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;
// 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
}
off++;
}
prefix_end:
// REX prefix is only considered if it is the last prefix.
if (rex_off != off - 1)
prefix_rex = 0;
if (UNLIKELY(off >= len))
return FD_ERR_PARTIAL;
off += retval;
unsigned opcode_escape = 0;
if (buffer[off] == 0x0f)
{
if (UNLIKELY(off + 1 >= len))
@@ -342,16 +303,16 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
// VEX + 66/F3/F2/REX will #UD.
// Note: REX is also here only respected if it immediately precedes the
// opcode, in this case the VEX "prefix".
if (prefixes & (PREFIX_OPSZ|PREFIX_REP|PREFIX_REPNZ|PREFIX_REX))
if (prefix_66 || prefix_rep || prefix_rex)
return FD_ERR_UD;
uint8_t byte = buffer[off + 1];
prefixes |= byte & 0x80 ? 0 : PREFIX_REXR;
prefix_rex |= byte & 0x80 ? 0 : PREFIX_REXR;
if (buffer[off] == 0xc4) // 3-byte VEX
{
prefixes |= byte & 0x40 ? 0 : PREFIX_REXX;
prefix_rex |= 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;
prefix_rex |= mode != DECODE_64 || (byte & 0x20) ? 0 : PREFIX_REXB;
if (byte & 0x1c) // Bits 4:2 of opcode_escape must be clear.
return FD_ERR_UD;
opcode_escape = (byte & 0x03) | 4; // 4 is table index with VEX
@@ -360,13 +321,14 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
if (UNLIKELY(off + 2 >= len))
return FD_ERR_PARTIAL;
byte = buffer[off + 2];
prefixes |= byte & 0x80 ? PREFIX_REXW : 0;
prefix_rex |= byte & 0x80 ? PREFIX_REXW : 0;
}
else // 2-byte VEX
opcode_escape = 1 | 4; // 4 is table index with VEX, 0f escape
prefixes |= byte & 0x04 ? PREFIX_VEXL : 0;
mandatory_prefix = byte & 0x03;
prefix_rex |= byte & 0x04 ? PREFIX_VEXL : 0;
prefix_rep = (byte & 2) ? (byte & 3) : 0;
prefix_66 = (byte & 3) == 1;
vex_operand = ((byte & 0x78) >> 3) ^ 0xf;
off += buffer[off] == 0xc4 ? 3 : 2;
@@ -380,13 +342,11 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
// Handle mandatory prefixes (which behave like an opcode ext.).
if (kind == ENTRY_TABLE_PREFIX)
{
// If a prefix is mandatory and used as opcode extension, it has no
// further effect on the instruction. This, however, does not completely
// apply to the 66 prefix: in rare cases it may affect the size of
// general purpose registers. The instruction descriptor encodes whether
// the 66 prefix has an effect on the instruction (IGN66).
prefixes &= ~(PREFIX_REPNZ | PREFIX_REP);
// If there is no REP/REPNZ prefix offer 66h as mandatory prefix. If
// there is a REP prefix, then the 66h prefix is ignored here.
uint8_t mandatory_prefix = prefix_rep ? prefix_rep : !!prefix_66;
table_idx = table_walk(table_idx, mandatory_prefix, &kind);
prefix_rep = 0; // Don't include REP/REPNZ in instr flags
}
// Then, walk through ModR/M-encoded opcode extensions.
@@ -402,8 +362,8 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
if (kind == ENTRY_TABLE_VEX)
{
uint8_t index = 0;
index |= prefixes & PREFIX_REXW ? (1 << 0) : 0;
index |= prefixes & PREFIX_VEXL ? (1 << 1) : 0;
index |= prefix_rex & PREFIX_REXW ? (1 << 0) : 0;
index |= prefix_rex & PREFIX_VEXL ? (1 << 1) : 0;
table_idx = table_walk(table_idx, index, &kind);
}
@@ -413,7 +373,10 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
struct InstrDesc* desc = (struct InstrDesc*) &_decode_table[table_idx];
instr->type = desc->type;
instr->flags = prefixes & 0x7f;
instr->flags = prefix_rep == 2 ? FD_FLAG_REP :
prefix_rep == 3 ? FD_FLAG_REPNZ : 0;
if (prefix_lock)
instr->flags |= FD_FLAG_LOCK;
if (mode == DECODE_64)
instr->flags |= FD_FLAG_64;
instr->address = address;
@@ -421,20 +384,20 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
unsigned op_size = 4;
if (DESC_OPSIZE(desc) == 2 && mode == DECODE_64) // DEF64
op_size = 8;
if ((prefixes & PREFIX_OPSZ) && !DESC_IGN66(desc)) // opsize override
if (prefix_66 && !DESC_IGN66(desc)) // opsize override
op_size = 2;
if (mode == DECODE_64 && (prefixes & PREFIX_REXW || DESC_OPSIZE(desc) == 3))
if (mode == DECODE_64 && (prefix_rex & PREFIX_REXW || DESC_OPSIZE(desc) == 3))
op_size = 8;
if (DESC_OPSIZE(desc) == 1) // force byte
op_size = 1;
uint8_t vec_size = 16;
if (prefixes & PREFIX_VEXL)
if (prefix_rex & PREFIX_VEXL)
vec_size = 32;
// Compute address size.
uint8_t addr_size = mode == DECODE_64 ? 8 : 4;
if (UNLIKELY(prefixes & PREFIX_ADDRSZ))
if (UNLIKELY(prefix_67))
addr_size >>= 1;
instr->addrsz = addr_size;
@@ -462,8 +425,9 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
if (DESC_HAS_MODREG(desc))
operand2 = &instr->operands[DESC_MODREG_IDX(desc)];
retval = decode_modrm(buffer + off, len - off, mode, instr, prefixes,
DESC_VSIB(desc), operand1, operand2);
int retval = decode_modrm(buffer + off, len - off, mode, instr,
prefix_rex, DESC_VSIB(desc), operand1,
operand2);
if (UNLIKELY(retval < 0))
return retval;
off += retval;
@@ -475,7 +439,7 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
uint8_t reg_idx = buffer[off - 1] & 7;
#if defined(ARCH_X86_64)
// Only used for GP registers, therefore always apply REX.B.
reg_idx += prefixes & PREFIX_REXB ? 8 : 0;
reg_idx += prefix_rex & PREFIX_REXB ? 8 : 0;
#endif
operand->type = FD_OT_REG;
operand->reg = reg_idx;
@@ -555,7 +519,7 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
imm_size = 3;
else if (op_size == 2)
imm_size = 2;
else if (mode == DECODE_64 && (prefixes & PREFIX_REXW) &&
else if (mode == DECODE_64 && (prefix_rex & PREFIX_REXW) &&
instr->type == FDI_MOVABS)
imm_size = 8;
else
@@ -600,7 +564,7 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
}
}
if (UNLIKELY(prefixes & PREFIX_LOCK))
if (UNLIKELY(prefix_lock))
if (!DESC_LOCK(desc) || instr->operands[0].type != FD_OT_MEM)
return FD_ERR_UD;
@@ -618,7 +582,7 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
// if (operand->type == FD_OT_REG && operand->misc == FD_RT_GPL &&
// !(prefixes & PREFIX_REX) && operand->size == 1 && operand->reg >= 4)
if (!(prefixes & PREFIX_REX) && (LOAD_LE_4(operand) & 0xfffcffff) == 0x01040101)
if (!(prefix_rex & PREFIX_REX) && (LOAD_LE_4(operand) & 0xfffcffff) == 0x01040101)
operand->misc = FD_RT_GPH;
}