[cfe-dev] The %p conversion and cast to void*

[David Blaikie]

On Tue, Feb 24, 2015 at 9:50 AM, Seth Cantrell <seth.cantrell at gmail.com>
wrote:

> It seems reasonable for this kind of warning to go under some -pedantic
> flag, something like "-Wformat-pedantic".
>

Possibly, though there's also a general aversion to adding off-by-default
warnings to clang because they end up undertested and a burden on the
codebase (in terms of complexity, etc) with relatively little value.


>
> > On Feb 24, 2015, at 12:31 PM, David Chisnall <
> David.Chisnall at cl.cam.ac.uk> wrote:
> >
> > On 21 Feb 2015, at 03:56, Rouben Rostamian <rostamian at umbc.edu> wrote:
> >>
> >> My question is: Why is it that removing the cast /does not/
> >> trigger a warning in Clang?  Do I need to specify further
> >> compilation flags to get that warning?
> >
> > It used to generate a warning in clang but it was spectacularly annoying
> and so was removed because it generated a huge number of false positives.
> The C standard does require that the argument for %p 'be a pointer to
> void', but the only platforms where any other data pointer (in the same
> address space) would be problematic are ones that do not natively support
> byte addressing and so need different pointer types for char* and void* and
> anything word aligned.  Clang does not support any such architectures and a
> lot of C code that people compile with clang / gcc would break on such
> architectures.
> >
> > The choice is to either have a warning that you are violating the letter
> of the C spec, but that your code will still work on every platform that
> you're likely to ever care about (and I say this as someone working on an
> architecture with a very unusual pointer representation, for which this
> warning would *still* be a false positive), or to allow this code through.
> >
> > Clang policy is that good code ought to be able to use -Wall -Werror by
> default, because warnings that have too high a false positive rate are not
> present.  If warnings are too likely to produce false positives (i.e. flag
> things that work fine on every system where the code is plausibly likely to
> run), then it doesn't help the programmer, it just makes them turn off the
> warning.
> >
> > David
> >
> >
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>
>
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