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

From: Peter Maydell
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH] build: Work around SIZE_MAX bug in OSX headers
Date: Tue, 12 Jul 2016 20:35:26 +0100

On 12 July 2016 at 19:23, Eric Blake <address@hidden> wrote:
> This violates POSIX, which requires that:
> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/stdint.h.html#tag_13_48
> "Each instance of these macros shall be replaced by a constant
> expression suitable for use in #if preprocessing directives, and this
> expression shall have the same type as would an expression that is an
> object of the corresponding type converted according to the integer
> promotions."
> That is, it is valid C to write '#if SIZE_MAX == 0xffffffff', while my
> replacement fails that test:
> foo.c:6:26: error: missing binary operator before token "("
>  #define SIZE_MAX ((sizeof(char)) * -1)
>                           ^
> foo.c:7:5: note: in expansion of macro ‘SIZE_MAX’

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.)

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

-- PMM

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