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

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 10/16/2017 01:32 PM, 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). 

Why doesn't this affect the rest of the hypervisor too, since we don't
save and restore the *mm registers?

> 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.

Sorry, just to clarify: You mean that there are standard headers which
contain prototypes for functions which return floating point values; we
include those headers but do not call the functions; and adding the
#pragma to the command-line would cause the compiler to choke on the
prototypes (even though the functions are never actually called)?

 -George


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