Re: [Xen-devel] [PATCH] x86emul: keep compiler from using {x, y, z}mm registers itself

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 16/10/17 13:32, Jan Beulich wrote:
> Since the emulator acts on the live hardware registers, we need to
> prevent the compiler from using them e.g. for inlined memcpy() /
> memset() (as gcc7 does). We can't, however, set this from the command
> line, as otherwise the 64-bit build would face issues with functions
> returning floating point values and being declared in standard headers.
>
> As the pragma isn't available prior to gcc6, we need to invoke it
> conditionally. Luckily up to gcc6 we haven't seen generated code access
> SIMD registers beyond what our asm()s do.
>
> Reported-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> While this doesn't affect core functionality, I think it would still be
> nice for it to be allowed in for 4.10.

Agreed.

Has this been tested with Clang?  It stands a good chance of being
compatible, but we may need an && !defined(__clang__) included.

~Andrew

>
> --- a/tools/tests/x86_emulator/x86-emulate.h
> +++ b/tools/tests/x86_emulator/x86-emulate.h
> @@ -4,6 +4,11 @@
>  #include <stdint.h>
>  #include <stdlib.h>
>  #include <string.h>
> +
> +#if __GNUC__ >= 6
> +#pragma GCC target("no-sse")
> +#endif
> +
>  #include <xen/xen.h>
>  
>  #include <asm/msr-index.h>
>
>
>


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