linux-kernel - Re: [PATCH] perf bpf: Use ERR_CAST instead of ERR_PTR(PTR

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Message-ID: <20181127130306.GD15747@kernel.org>
Date:   Tue, 27 Nov 2018 10:03:06 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Wen Yang <wen.yang99@....com.cn>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, zhong.weidong@....com.cn,
        Julia Lawall <julia.lawall@...6.fr>,
        Wen Yang <yellowriver2010@...mail.com>
Subject: Re: [PATCH] perf bpf: Use ERR_CAST instead of ERR_PTR(PTR_ERR())

Em Tue, Nov 27, 2018 at 05:06:10PM +0800, Wen Yang escreveu:
> Use ERR_CAST inlined function instead of ERR_PTR(PTR_ERR(...)).
> This makes it more readable and also fix this warning detected
> by err_cast.cocci:
> tools/perf/util/bpf-loader.c:1606:11-18: WARNING: ERR_CAST can be used with op

Have you tried building perf with this patch applied?

[acme@...co perf]$ find tools/include/ -name "*.h"  | xargs grep ERR_CAST
[acme@...co perf]$

Its not there, you first have to grab a copy of ERR_CAST() from
include/linux/err.h and put it in tools/include/linux/err.h to then be
able to apply this patch and keep the tools building:

So, applying your patch I get:

[acme@...co perf]$ make O=/tmp/build/perf -C tools/perf install-bin
make: Entering directory '/home/acme/git/perf/tools/perf'
  BUILD:   Doing 'make -j8' parallel build
  INSTALL  trace_plugins
  CC       /tmp/build/perf/util/bpf-loader.o
util/bpf-loader.c: In function ‘bpf__setup_output_event’:
util/bpf-loader.c:1606:12: error: implicit declaration of function ‘ERR_CAST’; did you mean ‘ERR_PTR’? [-Werror=implicit-function-declaration]
     return ERR_CAST(op);
            ^~~~~~~~
            ERR_PTR
util/bpf-loader.c:1606:12: error: nested extern declaration of ‘ERR_CAST’ [-Werror=nested-externs]
util/bpf-loader.c:1606:12: error: returning ‘int’ from a function with return type ‘struct perf_evsel *’ makes pointer from integer without a cast [-Werror=int-conversion]
     return ERR_CAST(op);
            ^~~~~~~~~~~~
cc1: all warnings being treated as errors
mv: cannot stat '/tmp/build/perf/util/.bpf-loader.o.tmp': No such file or directory
make[4]: *** [/home/acme/git/perf/tools/build/Makefile.build:96: /tmp/build/perf/util/bpf-loader.o] Error 1
make[3]: *** [/home/acme/git/perf/tools/build/Makefile.build:139: util] Error 2
make[2]: *** [Makefile.perf:658: /tmp/build/perf/libperf-in.o] Error 2
make[1]: *** [Makefile.perf:215: sub-make] Error 2
make: *** [Makefile:110: install-bin] Error 2
make: Leaving directory '/home/acme/git/perf/tools/perf'
[acme@...co perf]$ git log --oneline -1
82acac0da3ff (HEAD -> perf/core) perf bpf: Use ERR_CAST instead of ERR_PTR(PTR_ERR())
[acme@...co perf]$


So I went on and added a prep patch adopting ERR_CAST(), then tools/perf
is back again building:

[acme@...co perf]$ git log --oneline -2
2a371d30dc43 (HEAD -> perf/core) perf record: Extend trace writing to multi AIO
decc44122cf0 perf record: Enable asynchronous trace writing
[acme@...co perf]$

Thanks, patch applied.

- Arnaldo

 
> Signed-off-by: Wen Yang <wen.yang99@....com.cn>
> CC: Peter Zijlstra <peterz@...radead.org>
> CC: Arnaldo Carvalho de Melo <acme@...nel.org>
> CC: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> CC: Jiri Olsa <jolsa@...hat.com>
> CC: Namhyung Kim <namhyung@...nel.org>
> CC: Julia Lawall <julia.lawall@...6.fr>
> CC: Wen Yang <yellowriver2010@...mail.com>
> CC: linux-kernel@...r.kernel.org
> ---
>  tools/perf/util/bpf-loader.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
> index f9ae1a993806..9a280647d829 100644
> --- a/tools/perf/util/bpf-loader.c
> +++ b/tools/perf/util/bpf-loader.c
> @@ -1603,7 +1603,7 @@ struct perf_evsel *bpf__setup_output_event(struct perf_evlist *evlist, const cha
>  
>  			op = bpf_map__add_newop(map, NULL);
>  			if (IS_ERR(op))
> -				return ERR_PTR(PTR_ERR(op));
> +				return ERR_CAST(op);
>  			op->op_type = BPF_MAP_OP_SET_EVSEL;
>  			op->v.evsel = evsel;
>  		}
> -- 
> 2.19.1

-- 

- Arnaldo