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[Qemu-devel] [PATCH 01/54] target/i386: Fix handling of VEX prefixes

From: Michael Roth
Subject: [Qemu-devel] [PATCH 01/54] target/i386: Fix handling of VEX prefixes
Date: Tue, 6 Feb 2018 13:14:22 -0600

From: Peter Maydell <address@hidden>

In commit e3af7c788b73a6495eb9d94992ef11f6ad6f3c56 we
replaced direct calls to to cpu_ld*_code() with calls
to the x86_ld*_code() wrappers which incorporate an
advance of s->pc. Unfortunately we didn't notice that
in one place the old code was deliberately not incrementing

@@ -4501,7 +4528,7 @@ static target_ulong disas_insn(DisasContext *s, CPUState 
             static const int pp_prefix[4] = {
-            int vex3, vex2 = cpu_ldub_code(env, s->pc);
+            int vex3, vex2 = x86_ldub_code(env, s);

             if (!CODE64(s) && (vex2 & 0xc0) != 0xc0) {
                 /* In 32-bit mode, bits [7:6] must be 11b,

This meant we were mishandling this set of instructions.
Remove the manual advance of s->pc for the "is VEX" case
(which is now done by x86_ldub_code()) and instead rewind
PC in the case where we decide that this isn't really VEX.

Signed-off-by: Peter Maydell <address@hidden>
Cc: address@hidden
Reported-by: Alexandro Sanchez Bach <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
(cherry picked from commit cfcca361d77142f25fb1128755084cf91faa4db7)
Signed-off-by: Michael Roth <address@hidden>
 target/i386/translate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/i386/translate.c b/target/i386/translate.c
index 088a9d9766..ed5b69d6af 100644
--- a/target/i386/translate.c
+++ b/target/i386/translate.c
@@ -4547,9 +4547,9 @@ static target_ulong disas_insn(DisasContext *s, CPUState 
             if (!CODE64(s) && (vex2 & 0xc0) != 0xc0) {
                 /* In 32-bit mode, bits [7:6] must be 11b,
                    otherwise the instruction is LES or LDS.  */
+                s->pc--; /* rewind the advance_pc() x86_ldub_code() did */
-            s->pc++;
             /* 4.1.1-4.1.3: No preceding lock, 66, f2, f3, or rex prefixes. */
             if (prefixes & (PREFIX_REPZ | PREFIX_REPNZ

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