Messages in this thread |  | | Date | Thu, 4 May 2017 12:50:34 -0700 | From | Matthias Kaehlcke <> | Subject | Re: [PATCH 2/2] kbuild: clang: Disable the 'duplicate-decl-specifier' warning |
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Hi Masahiro,
El Sun, Apr 30, 2017 at 11:01:11PM +0900 Masahiro Yamada ha dit:
> 2017-04-22 6:39 GMT+09:00 Matthias Kaehlcke <mka@chromium.org>: > > clang generates plenty of these warnings in different parts of the code. > > They are mostly caused by container_of() and other macros which declare > > a "const <type> *" variable for their internal use which triggers a > > "duplicate 'const' specifier" warning if the <type> is already const > > qualified. > > > > Wording-mostly-from: Michael Davidson <md@google.com> > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org> > > > > I think container_of() can be more simple, > dropping the 'const'. > > The following patch worked for me. > > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index 4c26dc3..d53672b 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -846,11 +846,9 @@ static inline void ftrace_dump(enum > ftrace_dump_mode oops_dump_mode) { } > * @ptr: the pointer to the member. > * @type: the type of the container struct this is embedded in. > * @member: the name of the member within the struct. > - * > */ > #define container_of(ptr, type, member) ({ \ > - const typeof( ((type *)0)->member ) *__mptr = (ptr); \ > - (type *)( (char *)__mptr - offsetof(type,member) );}) > + (type *)((void *)(ptr) - offsetof(type, member));}) > > /* Rebuild everything on CONFIG_FTRACE_MCOUNT_RECORD */ > #ifdef CONFIG_FTRACE_MCOUNT_RECORD
Thanks, this eliminates indeed a huge amount of these warnings.
The other big source of warnings is MODULE_DEVICE_TABLE which declares a const alias of a type that in most cases is already const. One possible solution would be to remove the 'additional' const qualifier, which might leave some tables non-const. Another option could be some hackery to suppress the warning just for the macro. Not sure if any of this would be acceptable.
> For also this one, > I'd like to try to fix the code rather than hiding warnings.
I totally agree with the general approach. My clang kernel builds started with plenty of warnings disabled. I fixed the code for most of them until I was left with these two extremely noisy ones, for which I didn't see a clear path.
Cheers
Matthias
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