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encode.c
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encode.c
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#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <fadec-enc.h>
#ifdef __GNUC__
#define LIKELY(x) __builtin_expect((x), 1)
#define UNLIKELY(x) __builtin_expect((x), 0)
#else
#define LIKELY(x) (x)
#define UNLIKELY(x) (x)
#endif
#define OPC_66 0x80000
#define OPC_F2 0x100000
#define OPC_F3 0x200000
#define OPC_REXW 0x400000
#define OPC_LOCK 0x800000
#define OPC_VEXL0 0x1000000
#define OPC_VEXL1 0x1800000
#define OPC_EVEXL0 0x2000000
#define OPC_EVEXL1 0x2800000
#define OPC_EVEXL2 0x3000000
#define OPC_EVEXL3 0x3800000
#define OPC_EVEXB 0x4000000
#define OPC_VSIB 0x8000000
#define OPC_67 FE_ADDR32
#define OPC_SEG_MSK 0xe0000000
#define OPC_JMPL FE_JMPL
#define OPC_MASK_MSK 0xe00000000
#define OPC_EVEXZ 0x1000000000
#define OPC_USER_MSK (OPC_67|OPC_SEG_MSK|OPC_MASK_MSK)
#define OPC_FORCE_SIB 0x2000000000
#define OPC_DOWNGRADE_VEX 0x4000000000
#define OPC_DOWNGRADE_VEX_FLIPW 0x40000000000
#define OPC_EVEX_DISP8SCALE 0x38000000000
#define OPC_GPH_OP0 0x200000000000
#define OPC_GPH_OP1 0x400000000000
#define EPFX_REX_MSK 0x43f
#define EPFX_REX 0x20
#define EPFX_EVEX 0x40
#define EPFX_REXR 0x10
#define EPFX_REXX 0x08
#define EPFX_REXB 0x04
#define EPFX_REXR4 0x02
#define EPFX_REXB4 0x01
#define EPFX_REXX4 0x400
#define EPFX_VVVV_IDX 11
static bool op_mem(FeOp op) { return op < 0; }
static bool op_reg(FeOp op) { return op >= 0; }
static bool op_reg_gpl(FeOp op) { return (op & ~0x1f) == 0x100; }
static bool op_reg_gph(FeOp op) { return (op & ~0x3) == 0x204; }
static bool op_reg_xmm(FeOp op) { return (op & ~0x1f) == 0x600; }
static int64_t op_mem_offset(FeOp op) { return (int32_t) op; }
static unsigned op_mem_base(FeOp op) { return (op >> 32) & 0xfff; }
static unsigned op_mem_idx(FeOp op) { return (op >> 44) & 0xfff; }
static unsigned op_mem_scale(FeOp op) { return (op >> 56) & 0xf; }
static unsigned op_reg_idx(FeOp op) { return op & 0xff; }
static bool op_imm_n(FeOp imm, unsigned immsz) {
if (immsz == 0 && !imm) return true;
if (immsz == 1 && (int8_t) imm == imm) return true;
if (immsz == 2 && (int16_t) imm == imm) return true;
if (immsz == 3 && (imm&0xffffff) == imm) return true;
if (immsz == 4 && (int32_t) imm == imm) return true;
if (immsz == 8 && (int64_t) imm == imm) return true;
return false;
}
static
unsigned
opc_size(uint64_t opc, uint64_t epfx)
{
unsigned res = 1;
if (UNLIKELY(opc & OPC_EVEXL0)) {
res += 4;
} else if (UNLIKELY(opc & OPC_VEXL0)) {
if (opc & (OPC_REXW|0x20000) || epfx & (EPFX_REXX|EPFX_REXB))
res += 3;
else
res += 2;
} else {
if (opc & OPC_LOCK) res++;
if (opc & OPC_66) res++;
if (opc & (OPC_F2|OPC_F3)) res++;
if (opc & OPC_REXW || epfx & EPFX_REX_MSK) res++;
if (opc & 0x30000) res++;
if (opc & 0x20000) res++;
}
if (opc & OPC_SEG_MSK) res++;
if (opc & OPC_67) res++;
if (opc & 0x8000) res++;
return res;
}
static
int
enc_opc(uint8_t** restrict buf, uint64_t opc, uint64_t epfx)
{
if (opc & OPC_SEG_MSK)
*(*buf)++ = (0x65643e362e2600 >> (8 * ((opc >> 29) & 7))) & 0xff;
if (opc & OPC_67) *(*buf)++ = 0x67;
if (opc & OPC_EVEXL0) {
*(*buf)++ = 0x62;
unsigned b1 = opc >> 16 & 7;
if (!(epfx & EPFX_REXR)) b1 |= 0x80;
if (!(epfx & EPFX_REXX)) b1 |= 0x40;
if (!(epfx & EPFX_REXB)) b1 |= 0x20;
if (!(epfx & EPFX_REXR4)) b1 |= 0x10;
if ((epfx & EPFX_REXB4)) b1 |= 0x08;
*(*buf)++ = b1;
unsigned b2 = opc >> 20 & 3;
if (!(epfx & EPFX_REXX4)) b2 |= 0x04;
b2 |= (~(epfx >> EPFX_VVVV_IDX) & 0xf) << 3;
if (opc & OPC_REXW) b2 |= 0x80;
*(*buf)++ = b2;
unsigned b3 = opc >> 33 & 7;
b3 |= (~(epfx >> EPFX_VVVV_IDX) & 0x10) >> 1;
if (opc & OPC_EVEXB) b3 |= 0x10;
b3 |= (opc >> 23 & 3) << 5;
if (opc & OPC_EVEXZ) b3 |= 0x80;
*(*buf)++ = b3;
} else if (opc & OPC_VEXL0) {
if (epfx & (EPFX_REXR4|EPFX_REXX4|EPFX_REXB4|(0x10<<EPFX_VVVV_IDX))) return -1;
bool vex3 = opc & (OPC_REXW|0x20000) || epfx & (EPFX_REXX|EPFX_REXB);
unsigned pp = opc >> 20 & 3;
*(*buf)++ = 0xc4 | !vex3;
unsigned b2 = pp | (opc & 0x800000 ? 0x4 : 0);
if (vex3) {
unsigned b1 = opc >> 16 & 3;
if (!(epfx & EPFX_REXR)) b1 |= 0x80;
if (!(epfx & EPFX_REXX)) b1 |= 0x40;
if (!(epfx & EPFX_REXB)) b1 |= 0x20;
*(*buf)++ = b1;
if (opc & OPC_REXW) b2 |= 0x80;
} else {
if (!(epfx & EPFX_REXR)) b2 |= 0x80;
}
b2 |= (~(epfx >> EPFX_VVVV_IDX) & 0xf) << 3;
*(*buf)++ = b2;
} else {
if (opc & OPC_LOCK) *(*buf)++ = 0xF0;
if (opc & OPC_66) *(*buf)++ = 0x66;
if (opc & OPC_F2) *(*buf)++ = 0xF2;
if (opc & OPC_F3) *(*buf)++ = 0xF3;
if (opc & OPC_REXW || epfx & (EPFX_REX_MSK)) {
unsigned rex = 0x40;
if (opc & OPC_REXW) rex |= 8;
if (epfx & EPFX_REXR) rex |= 4;
if (epfx & EPFX_REXX) rex |= 2;
if (epfx & EPFX_REXB) rex |= 1;
*(*buf)++ = rex;
}
if (opc & 0x30000) *(*buf)++ = 0x0F;
if ((opc & 0x30000) == 0x20000) *(*buf)++ = 0x38;
if ((opc & 0x30000) == 0x30000) *(*buf)++ = 0x3A;
}
*(*buf)++ = opc & 0xff;
if (opc & 0x8000) *(*buf)++ = (opc >> 8) & 0xff;
return 0;
}
static
int
enc_imm(uint8_t** restrict buf, uint64_t imm, unsigned immsz)
{
if (!op_imm_n(imm, immsz)) return -1;
for (unsigned i = 0; i < immsz; i++)
*(*buf)++ = imm >> 8 * i;
return 0;
}
static
int
enc_o(uint8_t** restrict buf, uint64_t opc, uint64_t epfx, uint64_t op0)
{
if (op_reg_idx(op0) & 0x8) epfx |= EPFX_REXB;
bool has_rex = opc & OPC_REXW || epfx & EPFX_REX_MSK;
if (has_rex && op_reg_gph(op0)) return -1;
if (enc_opc(buf, opc, epfx)) return -1;
*(*buf - 1) = (*(*buf - 1) & 0xf8) | (op_reg_idx(op0) & 0x7);
return 0;
}
static
int
enc_mr(uint8_t** restrict buf, uint64_t opc, uint64_t epfx, uint64_t op0,
uint64_t op1, unsigned immsz)
{
// If !op_reg(op1), it is a constant value for ModRM.reg
if (op_reg(op0) && (op_reg_idx(op0) & 0x8)) epfx |= EPFX_REXB;
if (op_reg(op0) && (op_reg_idx(op0) & 0x10))
epfx |= 0 ? EPFX_REXB4 : EPFX_REXX|EPFX_EVEX;
if (op_mem(op0) && (op_mem_base(op0) & 0x8)) epfx |= EPFX_REXB;
if (op_mem(op0) && (op_mem_base(op0) & 0x10)) epfx |= EPFX_REXB4;
if (op_mem(op0) && (op_mem_idx(op0) & 0x8)) epfx |= EPFX_REXX;
if (op_mem(op0) && (op_mem_idx(op0) & 0x10))
epfx |= opc & OPC_VSIB ? 0x10<<EPFX_VVVV_IDX : EPFX_REXX4;
if (op_reg(op1) && (op_reg_idx(op1) & 0x8)) epfx |= EPFX_REXR;
if (op_reg(op1) && (op_reg_idx(op1) & 0x10)) epfx |= EPFX_REXR4;
bool has_rex = opc & (OPC_REXW|OPC_VEXL0|OPC_EVEXL0) || (epfx & EPFX_REX_MSK);
if (has_rex && (op_reg_gph(op0) || op_reg_gph(op1))) return -1;
if (epfx & (EPFX_EVEX|EPFX_REXB4|EPFX_REXX4|EPFX_REXR4|(0x10<<EPFX_VVVV_IDX))) {
if (!(opc & OPC_EVEXL0)) return -1;
} else if (opc & OPC_DOWNGRADE_VEX) { // downgrade EVEX to VEX
// clear EVEX and disp8scale, set VEX
opc = (opc & ~(uint64_t) (OPC_EVEXL0|OPC_EVEX_DISP8SCALE)) | OPC_VEXL0;
if (opc & OPC_DOWNGRADE_VEX_FLIPW)
opc ^= OPC_REXW;
}
if (LIKELY(op_reg(op0))) {
if (enc_opc(buf, opc, epfx)) return -1;
*(*buf)++ = 0xc0 | ((op_reg_idx(op1) & 7) << 3) | (op_reg_idx(op0) & 7);
return 0;
}
unsigned opcsz = opc_size(opc, epfx);
int mod = 0, reg = op1 & 7, rm;
int scale = 0, idx = 4, base = 0;
int32_t off = op_mem_offset(op0);
bool withsib = opc & OPC_FORCE_SIB;
if (!!op_mem_idx(op0) != !!op_mem_scale(op0)) return -1;
if (!op_mem_idx(op0) && (opc & OPC_VSIB)) return -1;
if (op_mem_idx(op0))
{
if (opc & OPC_VSIB)
{
if (!op_reg_xmm(op_mem_idx(op0))) return -1;
// EVEX VSIB requires non-zero opmask
if ((opc & OPC_EVEXL0) && !(opc & OPC_MASK_MSK)) return -1;
}
else
{
if (!op_reg_gpl(op_mem_idx(op0))) return -1;
if (op_reg_idx(op_mem_idx(op0)) == 4) return -1;
}
idx = op_mem_idx(op0) & 7;
int scalabs = op_mem_scale(op0);
if (scalabs & (scalabs - 1)) return -1;
scale = (scalabs & 0xA ? 1 : 0) | (scalabs & 0xC ? 2 : 0);
withsib = true;
}
unsigned dispsz = 0;
if (!op_mem_base(op0))
{
base = 5;
rm = 4;
dispsz = 4;
}
else if (op_mem_base(op0) == FE_IP)
{
rm = 5;
dispsz = 4;
// Adjust offset, caller doesn't know instruction length.
off -= opcsz + 5 + immsz;
if (withsib) return -1;
}
else
{
if (!op_reg_gpl(op_mem_base(op0))) return -1;
rm = op_reg_idx(op_mem_base(op0)) & 7;
if (withsib || rm == 4) {
base = rm;
rm = 4;
}
if (off) {
unsigned disp8scale = (opc & OPC_EVEX_DISP8SCALE) >> 39;
if (!(off & ((1 << disp8scale) - 1)) && op_imm_n(off >> disp8scale, 1)) {
mod = 0x40;
dispsz = 1;
off >>= disp8scale;
} else {
mod = 0x80;
dispsz = 4;
}
} else if (rm == 5) {
mod = 0x40;
dispsz = 1;
}
}
if (opcsz + 1 + (rm == 4) + dispsz + immsz > 15) return -1;
if (enc_opc(buf, opc, epfx)) return -1;
*(*buf)++ = mod | (reg << 3) | rm;
if (UNLIKELY(rm == 4))
*(*buf)++ = (scale << 6) | (idx << 3) | base;
return enc_imm(buf, off, dispsz);
}
typedef enum {
ENC_NP, ENC_M, ENC_R,
ENC_M1, ENC_MI, ENC_MC, ENC_MR, ENC_RM, ENC_RMA, ENC_MRI, ENC_RMI, ENC_MRC,
ENC_AM, ENC_MA,
ENC_I, ENC_IA, ENC_O, ENC_OI, ENC_OA, ENC_S, ENC_A, ENC_D, ENC_FD, ENC_TD,
ENC_RVM, ENC_RVMI, ENC_RVMR, ENC_RMV, ENC_VM, ENC_VMI, ENC_MVR, ENC_MRV,
ENC_MAX
} Encoding;
struct EncodingInfo {
uint8_t modrm : 2;
uint8_t modreg : 2;
uint8_t vexreg : 2;
uint8_t immidx : 2;
uint8_t immctl : 3;
uint8_t zregidx : 2;
uint8_t zregval : 1;
};
const struct EncodingInfo encoding_infos[ENC_MAX] = {
[ENC_NP] = { 0 },
[ENC_M] = { .modrm = 0x0^3 },
[ENC_R] = { .modreg = 0x0^3 },
[ENC_M1] = { .modrm = 0x0^3, .immctl = 1, .immidx = 1 },
[ENC_MI] = { .modrm = 0x0^3, .immctl = 4, .immidx = 1 },
[ENC_MC] = { .modrm = 0x0^3, .zregidx = 0x1^3, .zregval = 1 },
[ENC_MR] = { .modrm = 0x0^3, .modreg = 0x1^3 },
[ENC_RM] = { .modrm = 0x1^3, .modreg = 0x0^3 },
[ENC_RMA] = { .modrm = 0x1^3, .modreg = 0x0^3, .zregidx = 0x2^3, .zregval = 0 },
[ENC_MRI] = { .modrm = 0x0^3, .modreg = 0x1^3, .immctl = 4, .immidx = 2 },
[ENC_RMI] = { .modrm = 0x1^3, .modreg = 0x0^3, .immctl = 4, .immidx = 2 },
[ENC_MRC] = { .modrm = 0x0^3, .modreg = 0x1^3, .zregidx = 0x2^3, .zregval = 1 },
[ENC_AM] = { .modrm = 0x1^3, .zregidx = 0x0^3, .zregval = 0 },
[ENC_MA] = { .modrm = 0x0^3, .zregidx = 0x1^3, .zregval = 0 },
[ENC_I] = { .immctl = 4, .immidx = 0 },
[ENC_IA] = { .zregidx = 0x0^3, .zregval = 0, .immctl = 4, .immidx = 1 },
[ENC_O] = { .modreg = 0x0^3 },
[ENC_OI] = { .modreg = 0x0^3, .immctl = 4, .immidx = 1 },
[ENC_OA] = { .modreg = 0x0^3, .zregidx = 0x1^3, .zregval = 0 },
[ENC_S] = { 0 },
[ENC_A] = { .zregidx = 0x0^3, .zregval = 0 },
[ENC_D] = { .immctl = 6, .immidx = 0 },
[ENC_FD] = { .zregidx = 0x0^3, .zregval = 0, .immctl = 2, .immidx = 1 },
[ENC_TD] = { .zregidx = 0x1^3, .zregval = 0, .immctl = 2, .immidx = 0 },
[ENC_RVM] = { .modrm = 0x2^3, .modreg = 0x0^3, .vexreg = 0x1^3 },
[ENC_RVMI] = { .modrm = 0x2^3, .modreg = 0x0^3, .vexreg = 0x1^3, .immctl = 4, .immidx = 3 },
[ENC_RVMR] = { .modrm = 0x2^3, .modreg = 0x0^3, .vexreg = 0x1^3, .immctl = 3, .immidx = 3 },
[ENC_RMV] = { .modrm = 0x1^3, .modreg = 0x0^3, .vexreg = 0x2^3 },
[ENC_VM] = { .modrm = 0x1^3, .vexreg = 0x0^3 },
[ENC_VMI] = { .modrm = 0x1^3, .vexreg = 0x0^3, .immctl = 4, .immidx = 2 },
[ENC_MVR] = { .modrm = 0x0^3, .modreg = 0x2^3, .vexreg = 0x1^3 },
[ENC_MRV] = { .modrm = 0x0^3, .modreg = 0x1^3, .vexreg = 0x2^3 },
};
static const uint64_t alt_tab[] = {
#include <fadec-encode-private.inc>
};
int
fe_enc64_impl(uint8_t** restrict buf, uint64_t opc, FeOp op0, FeOp op1,
FeOp op2, FeOp op3)
{
uint8_t* buf_start = *buf;
uint64_t ops[4] = {op0, op1, op2, op3};
uint64_t epfx = 0;
// Doesn't change between variants
if ((opc & OPC_GPH_OP0) && op_reg_gpl(op0) && op0 >= FE_SP)
epfx |= EPFX_REX;
else if (!(opc & OPC_GPH_OP0) && op_reg_gph(op0))
goto fail;
if ((opc & OPC_GPH_OP1) && op_reg_gpl(op1) && op1 >= FE_SP)
epfx |= EPFX_REX;
else if (!(opc & OPC_GPH_OP1) && op_reg_gph(op1))
goto fail;
try_encode:;
unsigned enc = (opc >> 51) & 0x1f;
const struct EncodingInfo* ei = &encoding_infos[enc];
int64_t imm = 0xcc;
unsigned immsz = (opc >> 47) & 0xf;
if (UNLIKELY(ei->zregidx && op_reg_idx(ops[ei->zregidx^3]) != ei->zregval))
goto next;
if (UNLIKELY(enc == ENC_S)) {
if ((op_reg_idx(op0) << 3 & 0x20) != (opc & 0x20)) goto next;
opc |= op_reg_idx(op0) << 3;
}
if (ei->immctl > 0) {
imm = ops[ei->immidx];
if (ei->immctl == 2) {
immsz = UNLIKELY(opc & OPC_67) ? 4 : 8;
if (immsz == 4) imm = (int32_t) imm; // address are zero-extended
}
if (ei->immctl == 3) {
if (!op_reg_xmm(imm)) goto fail;
imm = op_reg_idx(imm) << 4;
}
if (ei->immctl == 6) {
if (UNLIKELY(opc & FE_JMPL) && opc >> 56) goto next;
imm -= (int64_t) *buf + opc_size(opc, epfx) + immsz;
}
if (UNLIKELY(ei->immctl == 1) && imm != 1) goto next;
if (ei->immctl >= 2 && !op_imm_n(imm, immsz)) goto next;
}
// NOP has no operands, so this must be the 32-bit OA XCHG
if ((opc & 0xfffffff) == 0x90 && ops[0] == FE_AX) goto next;
if (UNLIKELY(enc == ENC_R)) {
if (enc_mr(buf, opc, epfx, 0, ops[0], immsz)) goto fail;
} else if (ei->modrm) {
FeOp modreg = ei->modreg ? ops[ei->modreg^3] : (opc & 0xff00) >> 8;
if (ei->vexreg)
epfx |= ((uint64_t) op_reg_idx(ops[ei->vexreg^3])) << EPFX_VVVV_IDX;
// Can fail for upgrade to EVEX due to high register numbers
if (enc_mr(buf, opc, epfx, ops[ei->modrm^3], modreg, immsz)) goto next;
} else if (ei->modreg) {
if (enc_o(buf, opc, epfx, ops[ei->modreg^3])) goto fail;
} else {
if (enc_opc(buf, opc, epfx)) goto fail;
}
if (ei->immctl >= 2)
if (enc_imm(buf, imm, immsz)) goto fail;
return 0;
next:;
uint64_t alt = opc >> 56;
if (alt) { // try alternative encoding, if available
opc = alt_tab[alt] | (opc & OPC_USER_MSK);
goto try_encode;
}
fail:
// Don't advance buffer on error; though we shouldn't write anything.
*buf = buf_start;
return -1;
}