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Re: [Qemu-devel] [PATCH v1 3/5] include/qemu/atomic.h: default to __atom

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH v1 3/5] include/qemu/atomic.h: default to __atomic functions
Date: Fri, 1 Apr 2016 15:51:53 +0100

On 1 April 2016 at 15:30, James Hogan <address@hidden> wrote:
> Hi Alex,
> On Thu, Jan 28, 2016 at 10:15:17AM +0000, Alex Bennée wrote:
>> The __atomic primitives have been available since GCC 4.7 and provide
>> a richer interface for describing memory ordering requirements. As a
>> bonus by using the primitives instead of hand-rolled functions we can
>> use tools such as the AddressSanitizer which need the use of well
>> defined APIs for its analysis.
>> If we have __ATOMIC defines we exclusively use the __atomic primitives
>> for all our atomic access. Otherwise we fall back to the mixture of
>> __sync and hand-rolled barrier cases.
>> Signed-off-by: Alex Bennée <address@hidden>
> This breaks the build on MIPS32, with the following link error:
> cpus.o: In function `icount_warp_rt':
> /work/mips/qemu/vz/cpus.c +343 : undefined reference to `__atomic_load_8'
> collect2: error: ld returned 1 exit status
> Seemingly __atomic_load_8 is provided by libatomic, so we're missing
> -latomic.

We should not be doing atomic ops on types larger than the native
pointer type. I think there's a patch proposed on list to fix this.
I don't think we should be adding libatomic.

-- PMM

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