Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 27 Jul 2018 10:59:23 -0700
From:   Jakub Kicinski <jakub.kicinski@netronome.com>
To:     Thomas Richter <tmricht@linux.ibm.com>
Cc:     daniel@iogearbox.net, ast@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, heiko.carstens@de.ibm.com,
        brueckner@linux.vnet.ibm.com, schwidefsky@de.ibm.com
Subject: Re: [PATCH] perf build: Build error in libbpf missing
 initialization
Message-ID: <20180727105923.2d5da6aa@cakuba.netronome.com>
In-Reply-To: <20180727082126.87530-1-tmricht@linux.ibm.com>
References: <20180727082126.87530-1-tmricht@linux.ibm.com>
Organization: Netronome Systems, Ltd.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, 27 Jul 2018 10:21:26 +0200, Thomas Richter wrote:
> In linux-next tree compiling the perf tool with additional make flags
> "EXTRA_CFLAGS=3D"-Wp,-D_FORTIFY_SOURCE=3D2 -O2"
> causes a compiler error. It is the warning
> 	'variable may be used uninitialized'
> which is treated as error:
>=20
> I compile it using a FEDORA 28 installation, my gcc compiler version:
> gcc (GCC) 8.0.1 20180324 (Red Hat 8.0.1-0.20)
>=20
> The file that causes the error is tools/lib/bpf/libbpf.c
>=20
> Here is the error message:
>=20
> [root@p23lp27] # make V=3D1 EXTRA_CFLAGS=3D"-Wp,-D_FORTIFY_SOURCE=3D2 -O2"
> [...]
> Makefile.config:849: No openjdk development package found, please
>    install JDK package, e.g. openjdk-8-jdk, java-1.8.0-openjdk-devel
> Warning: Kernel ABI header at 'tools/include/uapi/linux/if_link.h'
>         differs from latest version at 'include/uapi/linux/if_link.h'
>   CC       libbpf.o
> libbpf.c: In function =E2=80=98bpf_perf_event_read_simple=E2=80=99:
> libbpf.c:2342:6: error: =E2=80=98ret=E2=80=99 may be used uninitialized i=
n this
> 			function [-Werror=3Dmaybe-uninitialized]
>   int ret;
>       ^
> cc1: all warnings being treated as errors
> mv: cannot stat './.libbpf.o.tmp': No such file or directory
> /home6/tmricht/linux-next/tools/build/Makefile.build:96: recipe for targe=
t 'libbpf.o' failed
>=20
> Fix this warning and add an addition check at the beginning
> of the while loop.
>=20
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
>=20
> Suggested-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>

Ah, you already sent this, LGTM, thanks Thomas!

>  tools/lib/bpf/libbpf.c | 2 ++
>  1 file changed, 2 insertions(+)
>=20
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 73465caa33ba..66965ca96113 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -2349,6 +2349,8 @@ bpf_perf_event_read_simple(void *mem, unsigned long=
 size,
> =20
>  	begin =3D base + data_tail % size;
>  	end =3D base + data_head % size;
> +	if (begin =3D=3D end)
> +		return LIBBPF_PERF_EVENT_ERROR;
> =20
>  	while (begin !=3D end) {
>  		struct perf_event_header *ehdr;