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Re: [Qemu-devel] [PATCH] QEMU_BUILD_BUG_ON: use __COUNTER__

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH] QEMU_BUILD_BUG_ON: use __COUNTER__
Date: Tue, 31 Jan 2017 15:12:32 +0000

On 31 January 2017 at 15:03, Eric Blake <address@hidden> wrote:
> On 01/31/2017 08:43 AM, Michael S. Tsirkin wrote:
>> Some headers use QEMU_BUILD_BUG_ON. This causes a problem
>> if the C file including that header happens to have
>> QEMU_BUILD_BUG_ON at the same line number.
>> Fix using a widely available extension: __COUNTER__.
> gcc 4.3 and later; clang documents it but doesn't say when it was added.
>> If unavailable, provide a stub.
> What fails in our build farm if we don't provide the stub? Can we just
> require that our compiler is new enough to have __COUNTER__, or will
> that break some of our existing targets?

I think the problem is not so much our build farm (which is
I think all recent enough to postdate introduction of
__COUNTER__) but the probability of there being users
out there who are still using older compilers to build
QEMU releases. We don't need to enforce compile time
asserts on those old compilers but given that it's
trivial to avoid actually breaking the build for them,
why not provide the do-nothing fallback?

-- PMM

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