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target-i386: fix SIB decoding with index = 4

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A SIB byte with an index of 4 means "no scaled index", even if the scale
value is not 0. In 64-bit mode, if REX.X is used, an index of 4 selects
%r12. This is correctly handled by the computation of the index variable,
which includes the index bits, and also the REX.X prefix:

    index = ((code >> 3) & 7) | REX_X(s);

Thanks to Avi Kivity, Jamie Lokier and Malc for the analysis of the
problem and the initial patch.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Aurelien Jarno 2010-03-06 18:02:31 +01:00
parent 1298cb6804
commit b16f827bdf
1 changed files with 2 additions and 2 deletions
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4
target-i386/translate.c
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@ -2047,8 +2047,8 @@ static void gen_lea_modrm(DisasContext *s, int modrm, int *reg_ptr, int *offset_
gen_op_movl_A0_im(disp);
}
}
/* XXX: index == 4 is always invalid */
if (havesib && (index != 4 || scale != 0)) {
/* index == 4 means no index */
if (havesib && (index != 4)) {
#ifdef TARGET_X86_64
if (s->aflag == 2) {
gen_op_addq_A0_reg_sN(scale, index);