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decode: Encode trie node kind in 2 bits

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This commit is contained in:
Alexis Engelke
2023-03-22 10:46:35 +01:00
parent e1084be859
commit dac2ff1987
2 changed files with 59 additions and 50 deletions
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82
decode.c
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@@ -49,10 +49,8 @@ table_lookup(unsigned cur_idx, unsigned entry_idx) {
}
static unsigned
table_walk(unsigned cur_idx, unsigned entry_idx, unsigned* out_kind) {
unsigned entry = table_lookup(cur_idx, entry_idx);
*out_kind = entry & ENTRY_MASK;
return (entry & ~ENTRY_MASK) >> 1;
table_walk(unsigned table_entry, unsigned entry_idx) {
return table_lookup(table_entry & ~0x3, entry_idx);
}
#define LOAD_LE_1(buf) ((uint64_t) *(uint8_t*) (buf))
@@ -113,15 +111,14 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
// Ensure that we can actually handle the decode request
DecodeMode mode;
unsigned table_idx;
unsigned kind = ENTRY_TABLE_ROOT;
unsigned table_root_idx;
switch (mode_int)
{
#if defined(FD_TABLE_OFFSET_32)
case 32: table_idx = FD_TABLE_OFFSET_32; mode = DECODE_32; break;
case 32: table_root_idx = FD_TABLE_OFFSET_32; mode = DECODE_32; break;
#endif
#if defined(FD_TABLE_OFFSET_64)
case 64: table_idx = FD_TABLE_OFFSET_64; mode = DECODE_64; break;
case 64: table_root_idx = FD_TABLE_OFFSET_64; mode = DECODE_64; break;
#endif
default: return FD_ERR_INTERNAL;
}
@@ -153,7 +150,7 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
if (UNLIKELY(off >= len))
return FD_ERR_PARTIAL;
uint8_t prefix = buffer[off];
table_entry = table_lookup(table_idx, prefix);
table_entry = table_lookup(table_root_idx, prefix);
if (LIKELY(table_entry - 0xfff8 >= 8))
break;
prefixes[PF_REX] = 0;
@@ -173,22 +170,22 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
prefix_rep = prefixes[PF_REP];
}
kind = table_entry & ENTRY_MASK;
table_idx = (table_entry & ~ENTRY_MASK) >> 1;
if (LIKELY(kind != 7)) {
// table_entry kinds: INSTR(0), T16(1), ESCAPE_A(2), ESCAPE_B(3)
if (LIKELY(!(table_entry & 2))) {
off++;
// Then, walk through ModR/M-encoded opcode extensions.
if (kind == ENTRY_TABLE16 && LIKELY(off < len)) {
if (table_entry & 1) {
if (UNLIKELY(off >= len))
return FD_ERR_PARTIAL;
unsigned isreg = (buffer[off] & 0xc0) == 0xc0 ? 8 : 0;
table_idx = table_walk(table_idx, ((buffer[off] >> 3) & 7) | isreg, &kind);
if (kind == ENTRY_TABLE8E)
table_idx = table_walk(table_idx, buffer[off] & 7, &kind);
table_entry = table_walk(table_entry, ((buffer[off] >> 3) & 7) | isreg);
// table_entry kinds: INSTR(0), T8E(1)
if (table_entry & 1)
table_entry = table_walk(table_entry, buffer[off] & 7);
}
if (UNLIKELY(kind != ENTRY_INSTR))
return kind == 0 ? FD_ERR_UD : FD_ERR_PARTIAL;
// table_entry kinds: INSTR(0)
goto direct;
}
@@ -221,7 +218,8 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
return FD_ERR_PARTIAL;
if (UNLIKELY(mode == DECODE_32 && buffer[off + 1] < 0xc0)) {
off++;
table_idx = table_walk(table_idx, 0, &kind);
table_entry = table_walk(table_entry, 0);
// table_entry kinds: INSTR(0)
goto direct;
}
@@ -297,46 +295,56 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
}
}
table_idx = table_walk(table_idx, opcode_escape, &kind);
if (kind == ENTRY_TABLE256 && LIKELY(off < len))
table_idx = table_walk(table_idx, buffer[off++], &kind);
table_entry = table_walk(table_entry, opcode_escape);
// table_entry kinds: INSTR(0) [only for invalid], T256(2)
if (UNLIKELY(!table_entry))
return FD_ERR_UD;
if (UNLIKELY(off >= len))
return FD_ERR_PARTIAL;
table_entry = table_walk(table_entry, buffer[off++]);
// table_entry kinds: INSTR(0), T16(1), TVEX(2), TPREFIX(3)
// Handle mandatory prefixes (which behave like an opcode ext.).
if (kind == ENTRY_TABLE_PREFIX)
{
table_idx = table_walk(table_idx, mandatory_prefix, &kind);
}
if ((table_entry & 3) == 3)
table_entry = table_walk(table_entry, mandatory_prefix);
// table_entry kinds: INSTR(0), T16(1), TVEX(2)
// Then, walk through ModR/M-encoded opcode extensions.
if (kind == ENTRY_TABLE16 && LIKELY(off < len)) {
if (table_entry & 1) {
if (UNLIKELY(off >= len))
return FD_ERR_PARTIAL;
unsigned isreg = (buffer[off] & 0xc0) == 0xc0 ? 8 : 0;
table_idx = table_walk(table_idx, ((buffer[off] >> 3) & 7) | isreg, &kind);
if (kind == ENTRY_TABLE8E)
table_idx = table_walk(table_idx, buffer[off] & 7, &kind);
table_entry = table_walk(table_entry, ((buffer[off] >> 3) & 7) | isreg);
// table_entry kinds: INSTR(0), T8E(1), TVEX(2)
if (table_entry & 1)
table_entry = table_walk(table_entry, buffer[off] & 7);
}
// table_entry kinds: INSTR(0), TVEX(2)
// For VEX prefix, we have to distinguish between VEX.W and VEX.L which may
// be part of the opcode.
if (UNLIKELY(kind == ENTRY_TABLE_VEX))
if (UNLIKELY(table_entry & 2))
{
uint8_t index = 0;
index |= prefix_rex & PREFIX_REXW ? (1 << 0) : 0;
// When EVEX.L'L is the rounding mode, the instruction must not have
// L'L constraints.
index |= vexl << 1;
table_idx = table_walk(table_idx, index, &kind);
table_entry = table_walk(table_entry, index);
}
// table_entry kinds: INSTR(0)
if (UNLIKELY(kind != ENTRY_INSTR))
return kind == 0 ? FD_ERR_UD : FD_ERR_PARTIAL;
direct:
// table_entry kinds: INSTR(0)
if (UNLIKELY(!table_entry))
return FD_ERR_UD;
direct:;
static _Alignas(16) const struct InstrDesc descs[] = {
#define FD_DECODE_TABLE_DESCS
#include <fadec-decode-private.inc>
#undef FD_DECODE_TABLE_DESCS
};
const struct InstrDesc* desc = &descs[table_idx >> 2];
const struct InstrDesc* desc = &descs[table_entry >> 2];
instr->type = desc->type;
instr->addrsz = addr_size;