Re: Add forward declarations

On Tue, 2 Oct 2018 at 03:04, Craig Howland <[email protected]> wrote:
>
> On 10/01/2018 05:37 PM, Christophe Lyon wrote:
> > Hi,
> >
> > While building newlib for Aarch64, I noticed several warnings because
> > of missing prototypes. I am not familiar enough to know why the same
> > warnings do not appear when building for Arm.
> >
> > This patch adds the missing prototypes, tested by rebuilding for
> > Aarch64 and Arm, it removed the warnings and didn't generate any
> > error.
> >
> > OK?
> >
> > Christophe
> A primary reason for prototypes is that they are for checking, and fully-proper
> checking is a single header file that checks both the source providing the
> function as well as places that call the function.  That is, adding prototypes
> in the function definition file purely for the purposes of avoiding missing
> prototype warnings is missing the real usefulness behind the warning and giving
> a false sense of security.  (You'd be better off just taking
> -Wmissing-prototypes out of your options to avoid those particular warnings.)
> The prototypes need to be added to a header file, not the functions' own source.
>
> Put another way, as a general goal I'd think we ought to be fixing the cause of
> a warning to remove the warning, rather than doing things to "hide" or "mask"
> the warning (which could be considered as kludges).  Putting protoypes into the
> function source file is clearly masking the deficiency that there is not a
> header file with prototypes, rather than fixing the actual deficiency.  While
> there certainly are times when addressing the root cause of a warning is not
> possible, this does not seem to be one where it is appropriate. Probably
> something like sys/_syscall.h (or some such name) should be created and used.
> We should be cleaning up bad practice when it exists, not furthering it.  So,
> definitely a good thing to get rid of the warnings, but there is a much better
> approach to take in this case.
>
> Corrina or Jeff, any suggestions for a good place for syscall prototypes?  (My
> first thought was sys/syscalls.h, but the Linux syscall(2) manpage mentions that
> related to syscall() and "For SYS_xxx definitions."  Perhaps it would be OK, but
> perhaps not, too, which is why I ended up suggesting _syscall.h.)  Does someone
> know about a precedent in BSD or the like?
>

I agree with you, one of my intentions was precisely to get
knowledgeable feedback because this patch indeed looks a little bit
like a kludge :)

I've noticed that the prototypes are conditionally defined in
 newlib/libc/include/sys/unistd.h
under #ifdef _COMPILING_NEWLIB
but I'm not familiar enough with newlib build system to know if this
is the file to include or not.

In particular, as I said before, the warnings appear when building for
Aarch64 and not for Arm, so different code paths are used at least by
these two targets.


> Craig