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Re: [Qemu-block] [Qemu-devel] [PATCH] build: Work around SIZE_MAX bug in

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH] build: Work around SIZE_MAX bug in OSX headers
Date: Tue, 12 Jul 2016 14:22:51 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

On 07/12/2016 01:35 PM, Peter Maydell wrote:

> I tested this patch with a compile on OSX, and it does compile
> without warnings or errors. (NB: haven't tested that it
> fixes the warning that was being complained about in the
> other patchset.)

Ultimately, the combination of this patch plus the block patchset in
question is where we prove if it makes a positive difference, so if you
do have a chance to test it on OSX, that would be nice.  And that's true
whether we keep this version of the patch (with #if __APPLE__) or do a
second version based on a witness set at configure time, because the
interaction you're testing is if the replacement #define SIZE_MAX
silences the warning about printf(%zd).

> I don't have a very strong opinion about whether it's the
> best fix, but a couple of thoughts:
>  * my inclination is to prefer not to override system
>    headers except where we've checked and know they're broken
>    (ie in a future world where Apple get their headers right
>    I'd rather we automatically ended up using their version
>    rather than ours)

Indeed, a configure-based solution would avoid checkpatch.pl griping
about adding an #if __APPLE__.

And since glibc has the same bug with SSIZE_MAX, a configure-based
solution would be easier to copy-and-paste if we needed to work around
that too (then again, we don't have any use of SSIZE_MAX at the moment).

>  * we don't have any #if ...SIZE_MAX, but we do have some
>    for other kinds of _MAX constant.

I'll wait a bit longer to see if any other opinions surface, but sounds
like I'll probably be doing a v2 and trying for a configure solution.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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