Re: [PATCH v2 2/2] perf jevents: Enable warnings through HOSTCFLAGS

[John Garry]

On 21/10/2021 13:48, Jiri Olsa wrote:
> > +HOSTCFLAGS += -Wall
> > +HOSTCFLAGS += -Wextra
> > +
> >   # Enforce a non-executable stack, as we may regress (again) in the future by
> >   # adding assembler files missing the .GNU-stack linker note.
> >   LDFLAGS += -Wl,-z,noexecstack
> > diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> > index 7df13e74450c..118bcdc70bb4 100644
> > --- a/tools/perf/Makefile.perf
> > +++ b/tools/perf/Makefile.perf
> > @@ -226,7 +226,7 @@ else
> >   endif
> >   
> >   export srctree OUTPUT RM CC CXX LD AR CFLAGS CXXFLAGS V BISON FLEX AWK
> > -export HOSTCC HOSTLD HOSTAR
> > +export HOSTCC HOSTLD HOSTAR HOSTCFLAGS
> >   
> >   include $(srctree)/tools/build/Makefile.include
> >   
> > diff --git a/tools/perf/pmu-events/Build b/tools/perf/pmu-events/Build
> > index a055dee6a46a..d5c287f069a2 100644
> > --- a/tools/perf/pmu-events/Build
> > +++ b/tools/perf/pmu-events/Build
> > @@ -1,7 +1,7 @@
> >   hostprogs := jevents
> >   
> >   jevents-y	+= json.o jsmn.o jevents.o
> > -HOSTCFLAGS_jevents.o	= -I$(srctree)/tools/include
> > +HOSTCFLAGS_jevents.o	= -I$(srctree)/tools/include $(HOSTCFLAGS)
> so the the host cflags are made of:
>
> host_c_flags = -Wp,-MD,$(depfile) -Wp,-MT,$@ $(KBUILD_HOSTCFLAGS) -D"BUILD_STR(s)=\#s" $(HOSTCFLAGS_$(basetarget).o) $(HOSTCFLAGS_$(obj))

ok, so IIRC, then the rule for building .o from .c in 
tools/build/Makefile.build will pick up HOSTCFLAGS through this 
variable, so we then don't need to explicitly mention it in the 
per-target rule, so can have this as before in pmu-events/Build

HOSTCFLAGS_jevents.o	= -I$(srctree)/tools/include

right?

(Indeed I guess that we can get rid of -I$(srctree)/tools/include as well)

Thanks,
John


> can't you use KBUILD_HOSTCFLAGS?
>
> also perhaps we could rename KBUILD_HOSTCFLAGS to HOSTCFLAGS?
> the name seems like leftover from kbuild move
>
> jirka
>
> >   pmu-events-y	+= pmu-events.o
> >   JDIR		=  pmu-events/arch/$(SRCARCH)
> >   JSON		=  $(shell [ -d $(JDIR) ] &&