Re: [Xen-devel] [PATCH v12 1/4] x86emul: New return code for unimplemented instruction

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.09.17 at 07:12, <ppircalabu@xxxxxxxxxxxxxxx> wrote:

> Changed since v11:
>     * Fixed double negative in the patch description.
>     * Move assertion into the switch and use ASSERT_UNREACHABLE() when
>     applicable.
>     * Changed the description of X86EMUL_UNIMPLEMENTED / X86EMUL_UNRECOGNIZED
>     to reflect the differences between those 2 return codes.
>     * Changed the returned value to X86EMUL_UNRECOGNIZED in the
>     following cases:
>         X86EMUL_OPC(0x0f, 0x73): /* Group 14 */
>         X86EMUL_OPC_66(0x0f, 0x73):
>         X86EMUL_OPC_VEX_66(0x0f, 0x73):
>                 - All valid opcodes are defined, so it should return
>                 X86EMUL_UNRECOGNIZED if mod R/M bits are not matched.
> 
>         X86EMUL_OPC(0x0f, 0xc7) /* Group 9 */
>                 - For register type instructions all possible opcodes are
>                 defined, so it should return X86EMUL_UNRECOGNIZED if
>                 mod R/M bits are not matched.

This is not entirely correct, btw (and hence the code change isn't
either): The code there has a dependency on gas features, so
hypervisor builds may not include support for rdrand and/or rdseed.
You will want to add "#else" cases producing "unimplemented".

Jan


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