diff mbox

target-i386: fix SIB decoding with index = 4

Message ID 1267894951-12437-1-git-send-email-aurelien@aurel32.net
State New
Headers show

Commit Message

Aurelien Jarno March 6, 2010, 5:02 p.m. UTC 
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>
---
 target-i386/translate.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
diff mbox

Patch

diff --git a/target-i386/translate.c b/target-i386/translate.c
index a597e80..dc6f511 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);