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([2620:10d:c090:600::1:f0da]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-23ff71916f0sm87534415ad.147.2025.07.30.09.13.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Jul 2025 09:13:33 -0700 (PDT) Message-ID: Subject: Re: [PATCH] libbpf: avoid possible use of uninitialized mod_len From: Eduard Zingerman To: Yonghong Song , Achill Gilgenast , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Viktor Malik , bpf@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Martin KaFai Lau , Song Liu , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa Date: Wed, 30 Jul 2025 09:13:32 -0700 In-Reply-To: <49c6b3ba-7860-4b13-944f-5f503eb201fd@linux.dev> References: <20250729094611.2065713-1-fossdd@pwned.life> <49c6b3ba-7860-4b13-944f-5f503eb201fd@linux.dev> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2025-07-29 at 09:17 -0700, Yonghong Song wrote: >=20 > On 7/29/25 2:45 AM, Achill Gilgenast wrote: > > If not fn_name, mod_len does never get initialized which fails now with > > gcc15 on Alpine Linux edge: > >=20 > > libbpf.c: In function 'find_kernel_btf_id.constprop': > > libbpf.c:10100:33: error: 'mod_len' may be used uninitialized [-Werror= =3Dmaybe-uninitialized] > > 10100 | if (mod_name && strncmp(mod->name, mod_name, m= od_len) !=3D 0) > > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~= ~~~~~~~ > > libbpf.c:10070:21: note: 'mod_len' was declared here > > 10070 | int ret, i, mod_len; > > | ^~~~~~~ > >=20 > > Fixes: 8f8a024272f3 ("libbpf: support "module: Function" syntax for tra= cing programs") > > Signed-off-by: Achill Gilgenast >=20 > The code itself is actually okay. The error is triggered due to'maybe-uni= nitialized'. > To silence the compilation error, I think this change is okay. >=20 > Acked-by: Yonghong Song I agree with Yonghong, `mod_len` is only read if mod_name !=3D NULL, meaning that "if (fn_name) { ... mod_name =3D ...; mod_len =3D ... }" block was executed. Please drop the "Fixes" tag. Acked-by: Eduard Zingerman [...]