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Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targ
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets |
Date: |
Mon, 21 Mar 2016 15:36:45 +0000 |
User-agent: |
mu4e 0.9.17; emacs 25.0.92.7 |
Sean Bruno <address@hidden> writes:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA512
>
>
>
> On 03/21/16 02:11, Alex Bennée wrote:
>>
>> Peter Maydell <address@hidden> writes:
>>
>>> On 20 March 2016 at 19:20, Sean Bruno <address@hidden>
>>> 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
Odd, the comments say that vm_clock_warp start is protected by the
seqlock, and in fact every other access to it is a plain access. It
seems to me the code should probably just be:
seqlock_write_lock(&timers_state.vm_clock_seqlock);
if (vm_clock_warp_start !== -1 && runstate_is_running()) {
.. do stuff ..
}
vm_clock_warp_start = -1;
seqlock_write_unlock(&timers_state.vm_clock_seqlock);
if (we_did_stuff && qemu_clock_expired(QEMU_CLOCK_VIRTUAL)) {
qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
}
Paolo, does that seem sane to you?
--
Alex Bennée
- [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Sean Bruno, 2016/03/20
- Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Peter Maydell, 2016/03/20
- Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Alex Bennée, 2016/03/21
- Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Sean Bruno, 2016/03/21
- Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets,
Alex Bennée <=
- Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Paolo Bonzini, 2016/03/21
- Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Sean Bruno, 2016/03/22
- Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Alex Bennée, 2016/03/22
- Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Sean Bruno, 2016/03/28
- Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Sean Bruno, 2016/03/31
Re: [Qemu-devel] [FreeBSD] Host build i386 failing to build aarch64 targets, Paolo Bonzini, 2016/03/21