Re: [Xen-devel] [PATCH] x86/ioemul: Misc improvements to ioport_emulate.c

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 29/01/18 11:23, Jan Beulich wrote:
>>>> On 26.01.18 at 15:48, <andrew.cooper3@xxxxxxxxxx> wrote:
>> Put the opcode into an array and use memcpy.  This allows the compiled code 
>> to
>> be written with two movs, rather than 10 mov $imm8's.  Also, drop trailing
>> whitespace in the file.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> It's a clear improvement, so
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> but ...
>
>> @@ -11,32 +11,24 @@
>>  static bool ioemul_handle_proliant_quirk(
>>      u8 opcode, char *io_emul_stub, struct cpu_user_regs *regs)
>>  {
>> +    static const char stub[] = {
>> +        0x9c,       /*    pushf           */
>> +        0xfa,       /*    cli             */
>> +        0xee,       /*    out %al, %dx    */
>> +        0xec,       /* 1: in %dx, %al     */
>> +        0xa8, 0x80, /*    test $0x80, %al */
>> +        0x75, 0xfb, /*    jnz 1b          */
>> +        0x9d,       /*    popf            */
>> +        0xc3,       /*    ret             */
>> +    };
> ... could you go even further and avoid this hex encoding of insns
> altogether, but using a file scope asm(), or a function scope one
> putting this into e.g. .fixup via .pushsection/.popsection?

I tried that, but couldn't find a way of creating the blob as a static
in C's eyes, or the size out as a build-time constant.

~Andre

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