Messages in this thread | | | Subject | Re: [PATCH v2] sched/core: silence a warning in sched_init() | From | Qian Cai <> | Date | Thu, 18 Jul 2019 16:44:42 -0400 |
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> On Jun 25, 2019, at 11:57 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, Jun 25, 2019 at 11:07:09AM -0400, Qian Cai wrote: >> On Tue, 2019-06-25 at 16:25 +0200, Peter Zijlstra wrote: >>> On Tue, Jun 25, 2019 at 10:04:19AM -0400, Qian Cai wrote: >>>> On Tue, 2019-06-25 at 15:52 +0200, Peter Zijlstra wrote: >>>> Yes, -Wmissing-prototype makes no sense, but "-Wunused-but-set-variable" is >>>> pretty valid to catch certain developer errors. For example, >>>> >>>> https://lists.linuxfoundation.org/pipermail/iommu/2019-May/035680.html >>>> >>>>> >>>>> As to this one, ideally the compiler would not be stupid, and understand >>>>> the below, but alas. >>>> >>>> Pretty sure that won't work, as the compiler will complain something like, >>>> >>>> ISO C90 forbids mixed declarations and code >>> >>> No, it builds just fine, it's a new block and C allows new variables at >>> every block start -- with the scope of that block. >> >> I remember I tried that before but recalled the error code wrong. Here it is, >> >> kernel/sched/core.c:5940:17: warning: unused variable 'ptr' [-Wunused-variable] >> unsigned long ptr = (unsigned long)kzalloc(alloc_size, >> GFP_NOWAIT); > > Yes, I know, I tried. And GCC is a moron because of it.
Actually, not only GCC but clang also don’t understand your patch.
# make CC=clang W=1 kernel/sched/core.o
kernel/sched/core.c:6384:17: warning: unused variable 'ptr' [-Wunused-variable] unsigned long ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT);
Maybe adding a “__maybe_unused” until the day that compilers are getting smarter.
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