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

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Message-ID: <32d98804-7e56-e73b-4c66-8776dbf58ddf@huawei.com>
Date:   Thu, 28 Oct 2021 09:23:58 +0100
From:   John Garry <john.garry@...wei.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>
CC:     "peterz@...radead.org" <peterz@...radead.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "irogers@...gle.com" <irogers@...gle.com>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kjain@...ux.ibm.com" <kjain@...ux.ibm.com>,
        "james.clark@....com" <james.clark@....com>
Subject: Re: [PATCH v2 2/2] perf jevents: Enable warnings through HOSTCFLAGS

On 25/10/2021 17:20, Arnaldo Carvalho de Melo wrote:
> Em Mon, Oct 25, 2021 at 01:40:44PM +0200, Jiri Olsa escreveu:
>> On Fri, Oct 22, 2021 at 10:42:11AM +0100, John Garry wrote:
>>> 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)
>>
>> hm, the -I.. should stay no? I don't see that
>> it's being added soem other way
>>
>> jirka
>>
> 
> Probably this change from KBUILD_HOSTCFLAGS back to HOSTCFLAGS should
> come with this;
> 
> Cc: Laura Abbott <labbott@...hat.com>
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Fixes: 96f14fe738b69dd9 ("kbuild: Rename HOSTCFLAGS to KBUILD_HOSTCFLAGS")
> 
> Right?

Maybe, but then renaming back from KBUILD_HOSTCFLAGS -> HOSTCFLAGS seems 
odd as a fix

Anyway, now that this original series is in perf/core, I'll send patches 
on top with this change, cc'ing Laura and Masahiro

Thanks!