| Message ID | CAK7LNATD-KbP6GtV_j6NMgcPQYRigz5pA8fdos7hQSzQpL8czw@mail.gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi Matthias, 2017-05-05 4:50 GMT+09:00 Matthias Kaehlcke <mka@chromium.org>: > 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. I noticed this solution will drop precious type checking from container_of(). So, my workaround is not nice. > 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. Me neither. >> 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. If we do not come up with a good solution, I will pick up this patch.
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 */