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Add support for instructions which always use low 8-bit registers

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Add a byte code to explicitly support instructions which only uses the
low 8-bit registers (as if a REX prefix always was present.)  This is
usable for instructions which are officially documented as using "the
low byte of a 32-bit register" and so on.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin 2009-06-24 21:38:29 -07:00
parent f9fc3fde55
commit 9472dab6ed
3 changed files with 24 additions and 3 deletions
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18
assemble.c
View file

@ -88,13 +88,14 @@
* generates no code in the assembler)
* \323 - indicates fixed 64-bit operand size, REX on extensions only.
* \324 - indicates 64-bit operand size requiring REX prefix.
* \325 - instruction which always uses spl/bpl/sil/dil
* \330 - a literal byte follows in the code stream, to be added
* to the condition code value of the instruction.
* \331 - instruction not valid with REP prefix. Hint for
* disassembler only; for SSE instructions.
* \332 - REP prefix (0xF2 byte) used as opcode extension.
* \333 - REP prefix (0xF3 byte) used as opcode extension.
* \334 - LOCK prefix used instead of REX.R
* \334 - LOCK prefix used as REX.R (used in non-64-bit mode)
* \335 - disassemble a rep (0xF3 byte) prefix as repe not rep.
* \336 - force a REP(E) prefix (0xF2) even if not specified.
* \337 - force a REPNE prefix (0xF3) even if not specified.
@ -996,6 +997,10 @@ static int64_t calcsize(int32_t segment, int64_t offset, int bits,
ins->rex |= REX_W;
break;
case 0325:
ins->rex |= REX_NH;
break;
case 0330:
codes++, length++;
break;
@ -1117,6 +1122,14 @@ static int64_t calcsize(int32_t segment, int64_t offset, int bits,
ins->rex &= rex_mask;
if (ins->rex & REX_NH) {
if (ins->rex & REX_H) {
errfunc(ERR_NONFATAL, "instruction cannot use high registers");
return -1;
}
ins->rex &= ~REX_P; /* Don't force REX prefix due to high reg */
}
if (ins->rex & REX_V) {
int bad32 = REX_R|REX_W|REX_X|REX_B;
@ -1645,6 +1658,9 @@ static void gencode(int32_t segment, int64_t offset, int bits,
ins->rex |= REX_W;
break;
case 0325:
break;
case 0330:
*bytes = *codes++ ^ condval[ins->condition];
out(offset, segment, bytes, OUT_RAWDATA, 1, NO_SEG, NO_SEG);

8
disasm.c
View file

@ -135,7 +135,7 @@ static enum reg_enum whichreg(int32_t regflags, int regval, int rex)
return 0;
if (!(REG8 & ~regflags)) {
if (rex & REX_P)
if (rex & (REX_P|REX_NH))
return nasm_rd_reg8_rex[regval];
else
return nasm_rd_reg8[regval];
@ -153,7 +153,7 @@ static enum reg_enum whichreg(int32_t regflags, int regval, int rex)
if (!(REG_DREG & ~regflags))
return nasm_rd_dreg[regval];
if (!(REG_TREG & ~regflags)) {
if (rex & REX_P)
if (regval > 7)
return 0; /* TR registers are ill-defined with rex */
return nasm_rd_treg[regval];
}
@ -799,6 +799,10 @@ static int matches(const struct itemplate *t, uint8_t *data,
o_used = true;
break;
case 0325:
ins->rex |= REX_NH;
break;
case 0330:
{
int t = *r++, d = *data++;

1
nasm.h
View file

@ -600,6 +600,7 @@ enum ccode { /* condition code names */
#define REX_D 0x0100 /* Instruction uses DREX instead of REX */
#define REX_OC 0x0200 /* DREX suffix has the OC0 bit set */
#define REX_V 0x0400 /* Instruction uses VEX/XOP instead of REX */
#define REX_NH 0x0800 /* Instruction which doesn't use high regs */
/*
* REX_V "classes" (prefixes which behave like VEX)