On Fri, Oct 12, 2018 at 9:01 AM James Bottomley [off-list ref] wrote:

On Fri, 2018-10-12 at 10:53 -0500, Denis Kenzior wrote:

quoted

Hi James,

quoted

quoted

  From the links provided in the patch it seems that one cannot
pass char/float/short to va_start().  Fair enough.  So if we make
h3 an unsigned int, the issue goes away, no?

For the current version of clang, yes.  However, if we're fixing
this for good a char * pointer is the only guaranteed thing because
it mirrors current use in printf.

All right.  I guess I wasn't aware that non-printf like variadic
functions are now considered harmful or of the impending crusade
against them :)

It's not, it's just a maintainer issue: The original problem is because
we coded for gcc specifically; it doesn't complain and does the right
thing, so everyone was happy.  Now Clang comes along and is unhappy
with this, so the question a good maintainer should ask is "how do I
fix this so it never comes back again?", not "what's the easiest
bandaid to get both Clang and gcc to work?" because the latter is how
we got here in the first place.

Clang is simply pointing out that this is explicitly undefined
behavior by the C90 spec.  As such, not only may the implementation be
different between compilers, but it is free to change between versions
of the same compiler (I haven't witnessed such a case yet in my
limited career, but I would never say never when it comes to relying
on undefined behavior).

James

quoted

But in the context of this patch, can we please use something less
invasive than changing all the arguments around?  Promoting h3 to a
bool (if possible) or int/unsigned int would get my vote.

Regards,
-Denis

-- 
Thanks,
~Nick Desaulniers