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

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Date:   Fri, 22 Oct 2021 10:42:11 +0100
From:   John Garry <john.garry@...wei.com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     <peterz@...radead.org>, <acme@...nel.org>, <mark.rutland@....com>,
        <alexander.shishkin@...ux.intel.com>, <namhyung@...nel.org>,
        <mingo@...hat.com>, <irogers@...gle.com>,
        <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kjain@...ux.ibm.com>, <james.clark@....com>
Subject: Re: [PATCH v2 2/2] perf jevents: Enable warnings through HOSTCFLAGS

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) ] &&