target/i386: Fix decoding of certain BMI instructions

This patch fixes a translation bug for a subset of x86 BMI instructions
such as the following:

   c4 e2 f9 f7 c0                shlxq   %rax, %rax, %rax

Currently, these incorrectly generate an undefined instruction exception
when SSE is disabled via CR4, while instructions like "shrxq" work fine.

The problem appears to be related to BMI instructions encoded using VEX
and with a mandatory prefix of "0x66" (data). Instructions with this
data prefix (such as shlxq) are currently rejected. Instructions with
other mandatory prefixes (such as shrxq) translate as expected.

This patch removes the incorrect check in "gen_sse" that causes the
exception to be generated. For the non-BMI cases, the check is
redundant: prefixes are already checked at line 3696.

Buglink: https://bugs.launchpad.net/qemu/+bug/1748296
Signed-off-by: David Greenaway <dgreenaway@google.com>
Message-Id: <20210114063958.1508050-1-dgreenaway@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
index 6a4c31f933b4252664aee2cf353f82103cd8b506..af1faf9342ba1f12478838c34d09ecbc8d1642b8 100644 (file)
--- a/target/i386/tcg/translate.c
+++ b/target/i386/tcg/translate.c
@@ -3075,7 +3075,7 @@ static void gen_sse(CPUX86State *env, DisasContext *s, int b,
     }
     if (is_xmm
         && !(s->flags & HF_OSFXSR_MASK)
-        && ((b != 0x38 && b != 0x3a) || (s->prefix & PREFIX_DATA))) {
+        && (b != 0x38 && b != 0x3a)) {
         goto unknown_op;
     }
     if (b == 0x0e) {