Messages in this thread | | | Date | Wed, 17 Apr 2024 01:52:28 +0100 | From | Matthew Wilcox <> | Subject | Re: [PATCH 00/19] Enable -Wshadow=local for kernel/sched |
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On Tue, Apr 16, 2024 at 05:29:02PM -0700, Linus Torvalds wrote: > On Tue, 16 Apr 2024 at 14:15, Kees Cook <keescook@chromium.org> wrote: > > > > I was looking at -Wshadow=local again, and remembered this series. It > > sounded like things were close, but a tweak was needed. What would be > > next to get this working? > > So what is the solution to > > #define MAX(a,b) ({ \ > typeof(a) __a = (a); \ > typeof(b) __b = (b); \ > __a > __b ? __a : __b; \ > })
#define __MAX(a, __a, b, __b) ({ \ typeof(a) __a = (a); \ typeof(b) __b = (b); \ __a > __b ? __a : __b; \ })
#define MAX(a, b) __MAX(a, UNIQUE_ID(a), b, UNIQUE_ID(b))
At least, I think that was the plan. This was two years ago and I've mostly forgotten.
> int test(int a, int b, int c) > { > return MAX(a, MAX(b,c)); > } > > where -Wshadow=all causes insane warnings that are bogus garbage? > > Honestly, Willy's patch-series is a hack to avoid this kind of very > natural nested macro pattern. > > But it's a horrible hack, and it does it by making the code actively worse. > > Here's the deal: if we can't handle somethng like the above without > warning, -Wshadow isn't getting enabled. > > Because we don't write worse code because of bad warnings. > > IOW, what is the sane way to just say "this variable can shadow the > use site, and it's fine"? > > Without that kind of out, I don't think -Wshadow=local is workable. > > Linus
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