From b16f827bdf7444b8cd338b9ecb654b4752f47225 Mon Sep 17 00:00:00 2001 From: Aurelien Jarno Date: Sat, 6 Mar 2010 18:02:31 +0100 Subject: [PATCH] target-i386: fix SIB decoding with index = 4 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 --- target-i386/translate.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/target-i386/translate.c b/target-i386/translate.c index 7a99e2055a..9dafc880bf 100644 --- a/target-i386/translate.c +++ b/target-i386/translate.c @@ -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);