Re: [PATCH] target/i386: Mark VPERMILPS as not valid with prefix 0

[Peter Maydell <peter.maydell@linaro.org>]

Obviously the subject prefix here should be "target/i386" -- fingers
on autopilot ;-)

-- PMM

On Fri, 14 Nov 2025 at 17:54, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> There are a small set of binary SSE insns which have no MMX
> equivalent, which we create the gen functions for with the
> BINARY_INT_SSE() macro.  This forwards to gen_binary_int_sse() with a
> NULL pointer for 'mmx'.
>
> For almost all of these insns we correctly mark them in the decode
> table as not permitting a zero prefix byte; however we got this wrong
> for VPERMILPS, with the result that a bogus instruction would get
> through the decode checks and end up in gen_binary_int_sse() trying
> to call a NULL pointer.
>
> Correct the decode table entry for VPERMILPD so that we get the
> expected #UD exception.
>
> In the x86 SDM, table A-4 "Three-byte Opcode Map: 08H-FFH
> (First Two Bytes are 0F 38H)" confirms that there is no pfx 0
> version of VPERMILPS.
>
> Cc: qemu-stable@nongnu.org
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3199
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  target/i386/tcg/decode-new.c.inc | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/i386/tcg/decode-new.c.inc b/target/i386/tcg/decode-new.c.inc
> index f4192f10068..805cfd08e83 100644
> --- a/target/i386/tcg/decode-new.c.inc
> +++ b/target/i386/tcg/decode-new.c.inc
> @@ -643,7 +643,7 @@ static const X86OpEntry opcodes_0F38_00toEF[240] = {
>      [0x0a] = X86_OP_ENTRY3(PSIGND,    V,x,        H,x,  W,x,  vex4 cpuid(SSSE3) mmx avx2_256 p_00_66),
>      [0x0b] = X86_OP_ENTRY3(PMULHRSW,  V,x,        H,x,  W,x,  vex4 cpuid(SSSE3) mmx avx2_256 p_00_66),
>      /* Listed incorrectly as type 4 */
> -    [0x0c] = X86_OP_ENTRY3(VPERMILPS, V,x,        H,x,  W,x,  vex6 chk(W0) cpuid(AVX) p_00_66),
> +    [0x0c] = X86_OP_ENTRY3(VPERMILPS, V,x,        H,x,  W,x,  vex6 chk(W0) cpuid(AVX) p_66),
>      [0x0d] = X86_OP_ENTRY3(VPERMILPD, V,x,        H,x,  W,x,  vex6 chk(W0) cpuid(AVX) p_66),
>      [0x0e] = X86_OP_ENTRY3(VTESTPS,   None,None,  V,x,  W,x,  vex6 chk(W0) cpuid(AVX) p_66),
>      [0x0f] = X86_OP_ENTRY3(VTESTPD,   None,None,  V,x,  W,x,  vex6 chk(W0) cpuid(AVX) p_66),
> --
> 2.43.0
>