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Re: [PATCH] Fix assert() warning in gcc < 4.8 [BZ# 21242]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: Justin Brewer <jzb0012 at auburn dot edu>, <libc-alpha at sourceware dot org>
- Date: Mon, 26 Jun 2017 10:56:45 +0000
- Subject: Re: [PATCH] Fix assert() warning in gcc < 4.8 [BZ# 21242]
- Authentication-results: sourceware.org; auth=none
- References: <6619e7e2-248e-08bc-6dc5-7b4d11bea3df@auburn.edu> <925e8a81-86f9-78a6-1578-660c04e39e3c@redhat.com> <alpine.DEB.2.20.1703211617300.8480@digraph.polyomino.org.uk> <b3e54310-9e08-c0fb-b0ee-b2a07711ef9a@redhat.com>
On Sun, 25 Jun 2017, Florian Weimer wrote:
> I think we can use __extension__ if we also expand the expression
> without __extension__ in an unevaluated context. The tricky part is to
> find one that is independent of GNU extensions.
> Perhaps this would work?
>
> # define assert(expr) \
> ((void) sizeof ((expr) == 0), __extension__ ({ \
> if (expr) \
> ; /* empty */ \
> else \
> __assert_fail (#expr, __FILE__, __LINE__, __FUNCTION__); \
> }))
>
> sizeof suppresses the evaluation of the first occurrence of expr. The
> comparison is needed because sizeof cannot be applied to function
> pointers and bitfields. C11 says that expr is compared to zero, so the
> (expr) == 0 expression is well-formed.
>
> What do you think? Should we make this change?
I think that's reasonable (appropriately commented to explain why it's
done that way).
--
Joseph S. Myers
joseph@codesourcery.com