Messages in this thread | | | Date | Thu, 4 Dec 2014 23:37:54 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] misc: suppress build warning |
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On Thu, 4 Dec 2014 08:30:32 -0800 Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> On Thu, Dec 04, 2014 at 03:13:00PM +0000, Prabhakar Lad wrote: > > On Thu, Dec 4, 2014 at 2:59 PM, Arnd Bergmann <arnd@arndb.de> wrote: > > > On Thursday 04 December 2014 14:38:30 Lad, Prabhakar wrote: > > >> this patch fixes following build warning: > > >> > > >> drivers/misc/ioc4.c: In function ___ioc4_probe___: > > >> drivers/misc/ioc4.c:194:16: warning: ___start___ may be used uninitialized in this function [-Wmaybe-uninitialized] > > >> period = (end - start) / > > >> ^ > > >> drivers/misc/ioc4.c:148:11: note: ___start___ was declared here > > >> uint64_t start, end, period; > > >> > > >> Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com> > > > > > > Please explain why the compiler thinks there is a bug, why you > > > are sure that there isn't, and why you picked '0' as the > > > initialization value. > > > > > Its a false positive, to suppress the warning '0' was picked. > > Are you _sure_ it's a false positive? That odd do/while loop looks like > it might just not ever initialize the start variable, are you sure the > logic there is correct? >
As long as IOC4_CALIBRATE_END is greater than IOC4_CALIBRATE_DISCARD (it is), `start' is written to.
It would be nice to simplify the code, but I'm not sure how.
And I really dislike this initialize-it-to-zero-to-stop-the-warning thing which we do all over the place. The reader doesn't know *why* it's initialized to zero and the initialization can conceal bugs if we get a code path which should have written to it but forgot to. And it adds unneeded code to vlinux.
I much prefer unintialized_var() which fixes the documentation issue and doesn't add code. But Linus and Ingo had a dummy-spit over it.
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