Em Fri, Jul 19, 2019 at 11:26:50AM -0700, Andrii Nakryiko escreveu: > On Fri, Jul 19, 2019 at 11:14 AM Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx> wrote: > > Em Fri, Jul 19, 2019 at 10:54:44AM -0700, Andrii Nakryiko escreveu: > > > Ok, did some more googling. This warning (turned error in your setup) > > > is emitted when -Wshadow option is enabled for GCC/clang. It appears > > > to be disabled by default, so it must be enabled somewhere for perf > > > build or something. > > Right, I came to the exact same conclusion, doing tests here: > > [perfbuilder@3a58896a648d tmp]$ gcc -Wshadow shadow_global_decl.c -o shadow_global_decl > > shadow_global_decl.c: In function 'main': > > shadow_global_decl.c:9: warning: declaration of 'link' shadows a global declaration > > shadow_global_decl.c:4: warning: shadowed declaration is here > > [perfbuilder@3a58896a648d tmp]$ gcc --version |& head -1 > > gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-23) > > [perfbuilder@3a58896a648d tmp]$ gcc shadow_global_decl.c -o shadow_global_decl > > [perfbuilder@3a58896a648d tmp]$ > > So I'm going to remove this warning from the places where it causes > > problems. > > > Would it be possible to disable it at least for libbpf when building > > > from perf either everywhere or for those systems where you see this > > > warning? I don't think this warning is useful, to be honest, just > > > random name conflict between any local and global variables will cause > > > this. > > Yeah, I might end up having this applied. > Thanks! So, I'm ending up with the patch below, there is some value after all in Wshadow, that is, from gcc 4.8 onwards :-) - Arnaldo diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include index 495066bafbe3..ded7a950dc40 100644 --- a/tools/scripts/Makefile.include +++ b/tools/scripts/Makefile.include @@ -32,7 +32,6 @@ EXTRA_WARNINGS += -Wno-system-headers EXTRA_WARNINGS += -Wold-style-definition EXTRA_WARNINGS += -Wpacked EXTRA_WARNINGS += -Wredundant-decls -EXTRA_WARNINGS += -Wshadow EXTRA_WARNINGS += -Wstrict-prototypes EXTRA_WARNINGS += -Wswitch-default EXTRA_WARNINGS += -Wswitch-enum @@ -69,8 +68,16 @@ endif # will do for now and keep the above -Wstrict-aliasing=3 in place # in newer systems. # Needed for the __raw_cmpxchg in tools/arch/x86/include/asm/cmpxchg.h +# +# See https://lkml.org/lkml/2006/11/28/253 and https://gcc.gnu.org/gcc-4.8/changes.html, +# that takes into account Linus's comments (search for Wshadow) for the reasoning about +# -Wshadow not being interesting before gcc 4.8. + ifneq ($(filter 3.%,$(MAKE_VERSION)),) # make-3 EXTRA_WARNINGS += -fno-strict-aliasing +EXTRA_WARNINGS += -Wno-shadow +else +EXTRA_WARNINGS += -Wshadow endif ifneq ($(findstring $(MAKEFLAGS), w),w)
