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

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Date:   Tue, 19 Oct 2021 09:37:23 +0100
From:   John Garry <john.garry@...wei.com>
To:     James Clark <james.clark@....com>, <peterz@...radead.org>,
        <acme@...nel.org>, <mark.rutland@....com>,
        <alexander.shishkin@...ux.intel.com>, <jolsa@...hat.com>,
        <namhyung@...nel.org>, <mingo@...hat.com>
CC:     <irogers@...gle.com>, <linux-perf-users@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <kjain@...ux.ibm.com>
Subject: Re: [PATCH 2/2] perf jevents: Enable warnings through HOSTCFLAGS

On 18/10/2021 11:41, James Clark wrote:
> 
> 
> On 15/10/2021 17:48, John Garry wrote:
>> Currently no compiler warnings at all are enabled for building jevents,
>> so help catch bugs at compile time by enabling through HOSTCFLAGS.
> 

Hi James,

> Is there any reason to not enable -Wall and -Werror so that it builds like
> the main project? Or if HOSTCFLAGS ends up being the same as CORE_CFLAGS
> then why not use CORE_CFLAGS instead?

I am not sure that we really want that, as CORE_CFLAGS brings with it 
things like _LARGEFILE64_SOURCE, which I doubt we want.

> 
> I added them like this and only one unused function needs to be removed to
> make it build successfully:
> 
> 
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 65934984f032..b2edcedf01db 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -18,6 +18,8 @@ detected_var = $(shell echo "$(1)=$($(1))" >> $(OUTPUT).config-detected)
>   
>   CFLAGS := $(EXTRA_CFLAGS) $(filter-out -Wnested-externs,$(EXTRA_WARNINGS))
>   HOSTCFLAGS := $(filter-out -Wnested-externs,$(EXTRA_WARNINGS))
> +HOSTCFLAGS += -Wall
> +HOSTCFLAGS += -Wextra
>   
>   include $(srctree)/tools/scripts/Makefile.arch
>   
> @@ -212,6 +214,7 @@ endif
>   ifneq ($(WERROR),0)
>     CORE_CFLAGS += -Werror
>     CXXFLAGS += -Werror
> +  HOSTCFLAGS += -Werror

These seem fine to add. Actually what I have in HOSTCFLAGS doesn't seem 
to detect unused functions, with one example fixed in b94729919db2.

Thanks,
John