| Message ID | 20210813224131.25803-1-rdunlap@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Makefile: use -Wno-main in the full kernel tree | expand |
On Fri, Aug 13, 2021 at 12:41 PM Randy Dunlap <rdunlap@infradead.org> wrote: > > Build-tested on most ARCHes. How about old versions of gcc? Or clang? From a quick google, it seems like '-Wmain' means something else for clang. But it is probably ok. Linus
On 8/13/21 5:01 PM, Linus Torvalds wrote: > On Fri, Aug 13, 2021 at 12:41 PM Randy Dunlap <rdunlap@infradead.org> wrote: >> >> Build-tested on most ARCHes. > > How about old versions of gcc? Or clang? > > From a quick google, it seems like '-Wmain' means something else for > clang. But it is probably ok. Dunno. Let's just let it ride in linux-next for a bit to see what it hits.
On Fri, 13 Aug 2021 15:41:31 -0700 Randy Dunlap <rdunlap@infradead.org> wrote: > When using gcc (SUSE Linux) 7.5.0 (on openSUSE 15.3), I see a > build warning: > > ../kernel/trace/trace_osnoise.c: In function 'start_kthread': > ../kernel/trace/trace_osnoise.c:1461:8: warning: 'main' is usually a function [-Wmain] > void *main = osnoise_main; > ^~~~ > > Quieten that warning by using "-Wno-main". It's OK to use "main" as a > declaration name in the kernel. > > Build-tested on most ARCHes. > > Signed-off-by: Randy Dunlap <rdunlap@infradead.org> > Suggested-by: Steven Rostedt <rostedt@goodmis.org> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Daniel Bristot de Oliveira <bristot@kernel.org> > Cc: Masahiro Yamada <masahiroy@kernel.org> > Cc: Michal Marek <michal.lkml@markovi.net> > Cc: linux-kbuild@vger.kernel.org > --- > Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- linux-next-20210812.orig/Makefile > +++ linux-next-20210812/Makefile > @@ -522,7 +522,7 @@ KBUILD_AFLAGS := -D__ASSEMBLY__ -fno-P > KBUILD_CFLAGS := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \ > -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \ > -Werror=implicit-function-declaration -Werror=implicit-int \ > - -Werror=return-type -Wno-format-security \ > + -Werror=return-type -Wno-format-security -Wno-main \ Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org> -- Steve > -std=gnu89 > KBUILD_CPPFLAGS := -D__KERNEL__ > KBUILD_RUST_TARGET := $(srctree)/arch/$(SRCARCH)/rust/target.json
On Fri, Aug 13, 2021 at 2:01 PM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > From a quick google, it seems like '-Wmain' means something else for > clang. But it is probably ok. So the warnings that clang gives with -Wmain seem to be much more reasonable. Which makes me think that the '-Wno-main' thing would likely be better as a gcc-only thing. Maybe something like this instead? Linus
On Mon, Aug 16, 2021 at 2:33 PM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > So the warnings that clang gives with -Wmain seem to be much more reasonable. In fact, I can't recreate the warning even with gcc and -Wmain. I get the feeling that this was a temporary misake in gcc, and perhaps only warns in a few very specific versions, and the gcc people already fixed this long ago. Oh well. Linus
On 8/16/21 5:38 PM, Linus Torvalds wrote: > On Mon, Aug 16, 2021 at 2:33 PM Linus Torvalds > <torvalds@linux-foundation.org> wrote: >> >> So the warnings that clang gives with -Wmain seem to be much more reasonable. > > In fact, I can't recreate the warning even with gcc and -Wmain. > > I get the feeling that this was a temporary misake in gcc, and perhaps > only warns in a few very specific versions, and the gcc people already > fixed this long ago. > > Oh well. That sounds likely. We can just ignore this if you had rather go that way.
On Mon, Aug 16, 2021 at 3:01 PM Randy Dunlap <rdunlap@infradead.org> wrote: > > That sounds likely. We can just ignore this if you had rather go that way. I'm happy doing it, I don't think the Wmain warnings buy anything for the kernel. My main worry is just that some compiler version might not support it at all or similar, and it would cause problems that way. Which is really the only reason why I'd like to narrow it down as much as (trivially) possible. It doesn't sound worth trying to pinpoint exact gcc version, but making it gcc-only would at least narrow it down a _bit_. Linus
On Mon, 16 Aug 2021 15:31:33 -1000 Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Mon, Aug 16, 2021 at 3:01 PM Randy Dunlap <rdunlap@infradead.org> wrote: > > > > That sounds likely. We can just ignore this if you had rather go that way. > > I'm happy doing it, I don't think the Wmain warnings buy anything for > the kernel. My main worry is just that some compiler version might not > support it at all or similar, and it would cause problems that way. > > Which is really the only reason why I'd like to narrow it down as much > as (trivially) possible. > > It doesn't sound worth trying to pinpoint exact gcc version, but > making it gcc-only would at least narrow it down a _bit_. Looks to me that -Wmain and -Wno-main have been in gcc for a long time. If we limit it to just gcc, I believe it will not be an issue for any compiler version the kernel supports. https://gcc.gnu.org/onlinedocs/gcc/Option-Index.html And perhaps you are correct, as this is not a new option (it's in all the gcc versions I have (tested back to 4.2.4)), and it didn't trigger for me, I too believe this was a bug in a particular version that Randy used. -- Steve
On 8/16/21 5:33 PM, Linus Torvalds wrote: > On Fri, Aug 13, 2021 at 2:01 PM Linus Torvalds > <torvalds@linux-foundation.org> wrote: >> >> From a quick google, it seems like '-Wmain' means something else for >> clang. But it is probably ok. > > So the warnings that clang gives with -Wmain seem to be much more reasonable. > > Which makes me think that the '-Wno-main' thing would likely be better > as a gcc-only thing. > > Maybe something like this instead? > > Linus Tested-by: Randy Dunlap <rdunlap@infradead.org> Should I resend the full patch? Thanks.
On 8/16/21 5:33 PM, Linus Torvalds wrote: > On Fri, Aug 13, 2021 at 2:01 PM Linus Torvalds > <torvalds@linux-foundation.org> wrote: >> >> From a quick google, it seems like '-Wmain' means something else for >> clang. But it is probably ok. > > So the warnings that clang gives with -Wmain seem to be much more reasonable. > > Which makes me think that the '-Wno-main' thing would likely be better > as a gcc-only thing. > > Maybe something like this instead? > > Linus > Linus, Can we get your version of this patch merged? Tested-by: Randy Dunlap <rdunlap@infradead.org> Should I resend the full patch? --- Makefile | 2 ++ 1 file changed, 2 insertions(+) diff --git a/Makefile b/Makefile index c19d1638da25..a33fba083df7 100644 --- a/Makefile +++ b/Makefile @@ -803,6 +803,8 @@ else # Disabled for clang while comment to attribute conversion happens and # https://github.com/ClangBuiltLinux/linux/issues/636 is discussed. KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough=5,) +# gcc inanely warns about local variables called 'main' +KBUILD_CFLAGS += -Wno-main endif # These warnings generated too much noise in a regular build.
--- linux-next-20210812.orig/Makefile +++ linux-next-20210812/Makefile @@ -522,7 +522,7 @@ KBUILD_AFLAGS := -D__ASSEMBLY__ -fno-P KBUILD_CFLAGS := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \ -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \ -Werror=implicit-function-declaration -Werror=implicit-int \ - -Werror=return-type -Wno-format-security \ + -Werror=return-type -Wno-format-security -Wno-main \ -std=gnu89 KBUILD_CPPFLAGS := -D__KERNEL__ KBUILD_RUST_TARGET := $(srctree)/arch/$(SRCARCH)/rust/target.json
When using gcc (SUSE Linux) 7.5.0 (on openSUSE 15.3), I see a build warning: ../kernel/trace/trace_osnoise.c: In function 'start_kthread': ../kernel/trace/trace_osnoise.c:1461:8: warning: 'main' is usually a function [-Wmain] void *main = osnoise_main; ^~~~ Quieten that warning by using "-Wno-main". It's OK to use "main" as a declaration name in the kernel. Build-tested on most ARCHes. Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Suggested-by: Steven Rostedt <rostedt@goodmis.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: Masahiro Yamada <masahiroy@kernel.org> Cc: Michal Marek <michal.lkml@markovi.net> Cc: linux-kbuild@vger.kernel.org --- Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)