freqs[sym] = (freqs[sym] >> 1) + 1;
}
+static inline s32
+find_next_opcode(const u8 *data, s32 i)
+{
+ /*
+ * The following table is used to accelerate the common case where the
+ * byte has nothing to do with x86 translation and must simply be
+ * skipped. This was faster than the following alternatives:
+ * - Jump table with 256 entries
+ * - Switch statement with default
+ */
+ static const u8 is_potential_opcode[256] = {
+ [0x48] = 1, [0x4C] = 1, [0xE8] = 1,
+ [0xE9] = 1, [0xF0] = 1, [0xFF] = 1,
+ };
+
+ for (;;) {
+ if (is_potential_opcode[data[++i]])
+ break;
+ if (is_potential_opcode[data[++i]])
+ break;
+ if (is_potential_opcode[data[++i]])
+ break;
+ if (is_potential_opcode[data[++i]])
+ break;
+ }
+ return i;
+}
+
+static inline s32
+translate_if_needed(u8 *data, s32 i, s32 *last_x86_pos,
+ s32 last_target_usages[], bool undo)
+{
+ s32 max_trans_offset;
+ s32 opcode_nbytes;
+ u16 target16;
+
+ max_trans_offset = LZMS_X86_MAX_TRANSLATION_OFFSET;
+
+ switch (data[i]) {
+ case 0x48:
+ if (data[i + 1] == 0x8B) {
+ if (data[i + 2] == 0x5 || data[i + 2] == 0xD) {
+ /* Load relative (x86_64) */
+ opcode_nbytes = 3;
+ goto have_opcode;
+ }
+ } else if (data[i + 1] == 0x8D) {
+ if ((data[i + 2] & 0x7) == 0x5) {
+ /* Load effective address relative (x86_64) */
+ opcode_nbytes = 3;
+ goto have_opcode;
+ }
+ }
+ break;
+ case 0x4C:
+ if (data[i + 1] == 0x8D) {
+ if ((data[i + 2] & 0x7) == 0x5) {
+ /* Load effective address relative (x86_64) */
+ opcode_nbytes = 3;
+ goto have_opcode;
+ }
+ }
+ break;
+ case 0xE8:
+ /* Call relative. Note: 'max_trans_offset' must be
+ * halved for this instruction. This means that we must
+ * be more confident that we are in a region of x86
+ * machine code before we will do a translation for this
+ * particular instruction. */
+ opcode_nbytes = 1;
+ max_trans_offset /= 2;
+ goto have_opcode;
+ case 0xE9:
+ /* Jump relative */
+ i += 4;
+ break;
+ case 0xF0:
+ if (data[i + 1] == 0x83 && data[i + 2] == 0x05) {
+ /* Lock add relative */
+ opcode_nbytes = 3;
+ goto have_opcode;
+ }
+ break;
+ case 0xFF:
+ if (data[i + 1] == 0x15) {
+ /* Call indirect */
+ opcode_nbytes = 2;
+ goto have_opcode;
+ }
+ break;
+ }
+
+ return i;
+
+have_opcode:
+ if (undo) {
+ if (i - *last_x86_pos <= max_trans_offset) {
+ void *p32 = &data[i + opcode_nbytes];
+ u32 n = get_unaligned_u32_le(p32);
+ put_unaligned_u32_le(n - i, p32);
+ }
+ target16 = i + get_unaligned_u16_le(&data[i + opcode_nbytes]);
+ } else {
+ target16 = i + get_unaligned_u16_le(&data[i + opcode_nbytes]);
+ if (i - *last_x86_pos <= max_trans_offset) {
+ void *p32 = &data[i + opcode_nbytes];
+ u32 n = get_unaligned_u32_le(p32);
+ put_unaligned_u32_le(n + i, p32);
+ }
+ }
+
+ i += opcode_nbytes + sizeof(le32) - 1;
+
+ if (i - last_target_usages[target16] <= LZMS_X86_ID_WINDOW_SIZE)
+ *last_x86_pos = i;
+
+ last_target_usages[target16] = i;
+
+ return i;
+}
+
/*
* Translate relative addresses embedded in x86 instructions into absolute
* addresses (@undo == %false), or undo this translation (@undo == %true).
/* Note: the very first byte must be ignored completely! */
i = 0;
for (;;) {
- s32 max_trans_offset;
- s32 opcode_nbytes;
- u16 target16;
-
- /*
- * The following table is used to accelerate the common case
- * where the byte has nothing to do with x86 translation and
- * must simply be skipped. This is the fastest (at least on
- * x86_64) of the implementations I tested. The other
- * implementations I tested were:
- * - Jump table with 256 entries
- * - Switch statement with default
- */
- static const u8 is_potential_opcode[256] = {
- [0x48] = 1, [0x4C] = 1, [0xE8] = 1,
- [0xE9] = 1, [0xF0] = 1, [0xFF] = 1,
- };
-
- for (;;) {
- if (is_potential_opcode[data[++i]])
- break;
- if (is_potential_opcode[data[++i]])
- break;
- if (is_potential_opcode[data[++i]])
- break;
- if (is_potential_opcode[data[++i]])
- break;
- }
+ i = find_next_opcode(data, i);
if (i >= tail_idx)
break;
- max_trans_offset = LZMS_X86_MAX_TRANSLATION_OFFSET;
- switch (data[i]) {
- case 0x48:
- if (data[i + 1] == 0x8B) {
- if (data[i + 2] == 0x5 || data[i + 2] == 0xD) {
- /* Load relative (x86_64) */
- opcode_nbytes = 3;
- goto have_opcode;
- }
- } else if (data[i + 1] == 0x8D) {
- if ((data[i + 2] & 0x7) == 0x5) {
- /* Load effective address relative (x86_64) */
- opcode_nbytes = 3;
- goto have_opcode;
- }
- }
- break;
- case 0x4C:
- if (data[i + 1] == 0x8D) {
- if ((data[i + 2] & 0x7) == 0x5) {
- /* Load effective address relative (x86_64) */
- opcode_nbytes = 3;
- goto have_opcode;
- }
- }
- break;
- case 0xE8:
- /* Call relative. Note: 'max_trans_offset' must be
- * halved for this instruction. This means that we must
- * be more confident that we are in a region of x86
- * machine code before we will do a translation for this
- * particular instruction. */
- opcode_nbytes = 1;
- max_trans_offset /= 2;
- goto have_opcode;
- case 0xE9:
- /* Jump relative */
- i += 4;
- break;
- case 0xF0:
- if (data[i + 1] == 0x83 && data[i + 2] == 0x05) {
- /* Lock add relative */
- opcode_nbytes = 3;
- goto have_opcode;
- }
- break;
- case 0xFF:
- if (data[i + 1] == 0x15) {
- /* Call indirect */
- opcode_nbytes = 2;
- goto have_opcode;
- }
- break;
- }
-
- continue;
-
- have_opcode:
- if (undo) {
- if (i - last_x86_pos <= max_trans_offset) {
- void *p32 = &data[i + opcode_nbytes];
- u32 n = get_unaligned_u32_le(p32);
- put_unaligned_u32_le(n - i, p32);
- }
- target16 = i + get_unaligned_u16_le(&data[i + opcode_nbytes]);
- } else {
- target16 = i + get_unaligned_u16_le(&data[i + opcode_nbytes]);
- if (i - last_x86_pos <= max_trans_offset) {
- void *p32 = &data[i + opcode_nbytes];
- u32 n = get_unaligned_u32_le(p32);
- put_unaligned_u32_le(n + i, p32);
- }
- }
-
- i += opcode_nbytes + sizeof(le32) - 1;
-
- if (i - last_target_usages[target16] <= LZMS_X86_ID_WINDOW_SIZE)
- last_x86_pos = i;
-
- last_target_usages[target16] = i;
-
- continue;
+ i = translate_if_needed(data, i, &last_x86_pos, last_target_usages, undo);
}
data[tail_idx + 8] = saved_byte;
git://wimlib.net / wimlib / commitdiff