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 <dgreena...@google.com> --- I'm a relative novice in both the QEMU source code and the x86 instruction set, so please do review carefully, and don't be afraid to let me know if I am completely going down the wrong path. This bug was originally reported at https://bugs.launchpad.net/qemu/+bug/1748296 a few years ago. The reproducer linked from the bug still fails on QEMU head, but is fixed by this patch. target/i386/tcg/translate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c index 6a4c31f933..af1faf9342 100644 --- 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) { -- 2.30.0.284.gd98b1dd5eaa7-goog
