From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Julien Grall <julien.grall@arm.com>
Subject: Re: [PATCH] x86emul: keep compiler from using {x, y, z}mm registers itself
Date: Mon, 16 Oct 2017 06:42:03 -0600 [thread overview]
Message-ID: <59E4C53B0200007800186B42@prv-mh.provo.novell.com> (raw)
In-Reply-To: <cec2488c-1e8f-bc9e-ddc6-e8f0d2a6fabc@citrix.com>
>>> On 16.10.17 at 14:37, <andrew.cooper3@citrix.com> wrote:
> 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@citrix.com>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> ---
>> 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?
Sorry, no - still haven't got around to set up a suitable Clang
locally.
> It stands a good chance of being
> compatible, but we may need an && !defined(__clang__) included.
Should non-gcc silently ignore "#pragma GCC ..." it doesn't
recognize, or not define __GNUC__ in the first place if it isn't
sufficiently compatible? I.e. if anything I'd expect we need
"#elif defined(__clang__)" to achieve the same for Clang by
some different pragma (if such exists).
Jan
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next prev parent reply other threads:[~2017-10-16 12:42 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-16 12:32 [PATCH] x86emul: keep compiler from using {x, y, z}mm registers itself Jan Beulich
2017-10-16 12:37 ` Andrew Cooper
2017-10-16 12:42 ` Jan Beulich [this message]
2017-11-06 11:59 ` Ping: " Jan Beulich
2017-11-06 15:04 ` George Dunlap
2017-11-13 16:22 ` Julien Grall
2017-11-21 13:26 ` Ping#2: " Jan Beulich
2017-11-21 13:29 ` Andrew Cooper
2017-11-22 16:09 ` Julien Grall
2017-10-16 15:05 ` George Dunlap
2017-10-16 15:44 ` Jan Beulich
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