From: Sean Bruno <sbruno@freebsd.org>
To: "Alex Bennée" <alex.bennee@linaro.org>,
"Peter Maydell" <peter.maydell@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets
Date: Mon, 21 Mar 2016 07:52:44 -0700 [thread overview]
Message-ID: <56F00ABC.9030700@freebsd.org> (raw)
In-Reply-To: <87vb4grya5.fsf@linaro.org>
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On 03/21/16 02:11, Alex Bennée wrote:
>
> Peter Maydell <peter.maydell@linaro.org> writes:
>
>> On 20 March 2016 at 19:20, Sean Bruno <sbruno@freebsd.org>
>> wrote:
>>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512
>>>
>>> aarch64 targets are now failing to build on i386 hosts due to
>>> missing __atomic_load_8() calls since this commit:
>>>
>>> https://github.com/qemu/qemu/commit/a0aa44b488b3601415d55041e4619aef5f3a4ba8#diff-c143d686899ae51d7b927d9c682e12fd
>>>
>>>
>>>
I'm unsure if Linux is disabling aarch64 targets for i386 hosts or if
>>> this commit works "just fine" on Linux hosts right now, as it
>>> doesn't work with clang or gcc.
>>
>> I think it just works on most Linux 32-bit architectures because
>> the compiler support can inline a suitable atomic op (there is
>> one case where it doesn't, which I think is PPC32).
>>
>> In any case, we mustn't use atomics on types larger than the host
>> pointer type, because it's not portable enough. Paolo or Alex,
>> can you have a look at this?
>
> I'll get a BSD up and running and check. What is triggering the
> __atomic_load_8 though?
>
>>
Specifically, its the atomic_read of vm_clock_warp_start in cpus.c:
114 /***********************************************************/
115 /* guest cycle counter */
116
117 /* Protected by TimersState seqlock */
118
119 static bool icount_sleep = true;
120 static int64_t vm_clock_warp_start = -1;
121 /* Conversion factor from emulated instructions to virtual clock
ticks. */
122 static int icount_time_shift;
....
339 static void icount_warp_rt(void)
340 {
341 /* The icount_warp_timer is rescheduled soon after
vm_clock_warp_start
342 * changes from -1 to another value, so the race here is okay.
343 */
344 if (atomic_read(&vm_clock_warp_start) == -1) {
345 return;
346 }
347
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next prev parent reply other threads:[~2016-03-21 14:52 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-20 19:20 [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets Sean Bruno
2016-03-20 20:03 ` Peter Maydell
2016-03-21 9:11 ` Alex Bennée
2016-03-21 14:52 ` Sean Bruno [this message]
2016-03-21 15:36 ` Alex Bennée
2016-03-21 15:56 ` Paolo Bonzini
2016-03-22 16:10 ` Sean Bruno
2016-03-22 16:22 ` Alex Bennée
2016-03-28 17:00 ` Sean Bruno
2016-03-31 16:57 ` Sean Bruno
2016-03-21 9:06 ` Paolo Bonzini
2016-03-21 9:35 ` Peter Maydell
2016-03-21 11:23 ` Paolo Bonzini
2016-03-21 11:49 ` Alex Bennée
2016-04-06 16:11 ` Sean Bruno
2016-04-06 18:51 ` Alex Bennée
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