Messages in this thread |  | | Subject | Re: [PATCH] x86: suppress sparse warning in copy_to_user() | From | Johannes Berg <> | Date | Tue, 04 Oct 2016 10:02:42 +0200 |
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On Tue, 2016-10-04 at 01:51 -0600, Jan Beulich wrote: > > > > > > > > > > > > > On 04.10.16 at 09:33, <johannes@sipsolutions.net> wrote: > > From: Johannes Berg <johannes.berg@intel.com> > > > > __compiletime_object_size() is simply defined to > > __builtin_object_size() > > which gcc declares with (void *, int type) prototype. > > If that was the case, everyone should have seen such warnings from > the day the original patch got introduced.
Only if they run sparse. Clearly people don't, or we wouldn't have a history of a ton of such problems, e.g.
112dc0c8069e ("locking/barriers: Suppress sparse warnings in lockless_dereference()") c15c0ab12fd6 ("ipv6: suppress sparse warnings in IP6_ECN_set_ce()") 1ea049b2de5d ("bvec: avoid variable shadowing warning")
(just to give a few of the examples I fixed recently). These are of course double-plus annoying in header files, since they show up in completely unrelated code when the header file is including, making the tools effectively useless.
> And the compiler warnings > I get when testing with all four combinations of const and volatile > also supports this by saying "expected 'const void *' but ..."
It's not a compiler warning though that I'm getting.
What tool are you using to get such a warning?
On gcc 6.1.1, I'm getting no warning (from the compiler) either way, even with W=2, and the gcc documentation notes the fact that it treats it as passing void *:
https://gcc.gnu.org/onlinedocs/gcc/Object-Size-Checking.html
> (arguably the compiler should accept volatile here too). To be > honest, for code in other trees where I'm maintainer, I'd reject such > casting away of constness, and demand the utility to get fixed > instead.
That could be done, but arguably "the tool" (I suppose you also never run sparse) is actually behaving correctly here - the "function" *is* defined to pass void *, so it's a correct warning.
Regardless though, it's fairly pointless to worry about it here since it's a builtin that's evaluated at compile time, so nothing can really happen.
johannes
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