El Wed, May 17, 2017 at 09:35:57AM +0200 Arnd Bergmann ha dit: > On Tue, May 16, 2017 at 11:41 PM, Doug Anderson <dianders@xxxxxxxxxxxx> wrote: > > Hi > > > > On Fri, Apr 21, 2017 at 2:39 PM, Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote: > >> 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@xxxxxxxxxx> > >> Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> > >> --- > >> Makefile | 1 + > >> 1 file changed, 1 insertion(+) > >> > >> diff --git a/Makefile b/Makefile > >> index df5abf346354..6cd6d428db43 100644 > >> --- a/Makefile > >> +++ b/Makefile > >> @@ -704,6 +704,7 @@ KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable) > >> KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier) > >> KBUILD_CFLAGS += $(call cc-disable-warning, gnu) > >> KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) > >> +KBUILD_CFLAGS += $(call cc-disable-warning, duplicate-decl-specifier) > >> # Quiet clang warning: comparison of unsigned expression < 0 is always false > >> KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare) > >> # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the > > > > It seems like gcc 7 may have the same warning. Specifically I saw a > > patch fly by from Arnd, which you can find in Mark Brown's tree now: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git/commit/?h=topic/rt5614&id=03ba791df98d15d07ea74075122af71e35c7611c > > > > > > +Arnd since he may be trying to solve the same issues? > > gcc-7 has a warning option with the same name, and I think I have > fixed all the occurrences we got in mainline (some patches my still > be in flight). However, it seems that only clang warns about > 'const typeof(type)' with 'type' being already const. > > I have not looked at clang warnings in a while, how many of these do > we get overall (aside from container_of)? We might be able > to turn off this particular warning by sprinkling in > '_Pragma("clang diagnostic push") _Pragma("clang diagnostic > ignored \"-Wduplicate-decl-specifier\"")' inside of the macro > (not sure if clang allows it there, gcc-4.4 and earlier I think did > not). > > It might also be useful to open a bug against clang so they can > change it in future releases, as the gcc behavior seems more > sensible in this instance. I asked our toolchain folks to follow up with the clang devs. They asked me for a simple test case, to my suprise clang didn't raise a warning when building this: static const int x; static const typeof(x) y; It turns out that the warning is only raised when -std=gnu89 (and potentially others) is set, which is the case of the kernel. Definitely looks like this should be fixed in clang. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
