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Wed, 19 Jun 2024 05:25:29 -0700 (PDT) Received: from ubuntu.localdomain ([124.126.129.60]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-705ccb3d19esm10500824b3a.122.2024.06.19.05.25.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Jun 2024 05:25:28 -0700 (PDT) From: Donglin Peng To: alan.maguire@oracle.com, eddyz87@gmail.com Cc: ast@kernel.org, daniel@iogearbox.net, song@kernel.org, andrii@kernel.org, haoluo@google.com, yonghong.song@linux.dev, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Donglin Peng Subject: [PATCH v2] libbpf: checking the btf_type kind when fixing variable offsets Date: Wed, 19 Jun 2024 05:23:55 -0700 Message-Id: <20240619122355.426405-1-dolinux.peng@gmail.com> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" I encountered an issue when building the test_progs from the repository[1]: $ pwd /work/Qemu/x86_64/linux-6.10-rc2/tools/testing/selftests/bpf/ $ make test_progs V=3D1 ... ./tools/sbin/bpftool gen object ./ip_check_defrag.bpf.linked2.o ./ip_check_= defrag.bpf.linked1.o libbpf: failed to find symbol for variable 'bpf_dynptr_slice' in section '.= ksyms' Error: failed to link './ip_check_defrag.bpf.linked1.o': No such file or di= rectory (2) ... Upon investigation, I discovered that the btf_types referenced in the '.ksy= ms' section had a kind of BTF_KIND_FUNC instead of BTF_KIND_VAR: $ bpftool btf dump file ./ip_check_defrag.bpf.linked1.o ... [2] DATASEC '.ksyms' size=3D0 vlen=3D2 type_id=3D16 offset=3D0 size=3D0 (FUNC 'bpf_dynptr_from_skb') type_id=3D17 offset=3D0 size=3D0 (FUNC 'bpf_dynptr_slice') ... [16] FUNC 'bpf_dynptr_from_skb' type_id=3D82 linkage=3Dextern [17] FUNC 'bpf_dynptr_slice' type_id=3D85 linkage=3Dextern ... For a detailed analysis, please refer to [2]. We can add a kind checking to fix the issue. [1] https://github.com/eddyz87/bpf/tree/binsort-btf-dedup [2] https://lore.kernel.org/all/0c0ef20c-c05e-4db9-bad7-2cbc0d6dfae7@oracle= .com/ Fixes: 8fd27bf69b86 ("libbpf: Add BPF static linker BTF and BTF.ext support= ") Acked-by: Eduard Zingerman Reviewed-by: Alan Maguire Signed-off-by: Donglin Peng --- v2: - Refactored the code using btf_is_var - Improved the comment to be more reasonable --- tools/lib/bpf/linker.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c index 0d4be829551b..5a583053e311 100644 --- a/tools/lib/bpf/linker.c +++ b/tools/lib/bpf/linker.c @@ -2213,10 +2213,17 @@ static int linker_fixup_btf(struct src_obj *obj) vi =3D btf_var_secinfos(t); for (j =3D 0, m =3D btf_vlen(t); j < m; j++, vi++) { const struct btf_type *vt =3D btf__type_by_id(obj->btf, vi->type); - const char *var_name =3D btf__str_by_offset(obj->btf, vt->name_off); - int var_linkage =3D btf_var(vt)->linkage; + const char *var_name; + int var_linkage; Elf64_Sym *sym; =20 + /* could be a variable or function */ + if (!btf_is_var(vt)) + continue; + + var_name =3D btf__str_by_offset(obj->btf, vt->name_off); + var_linkage =3D btf_var(vt)->linkage; + /* no need to patch up static or extern vars */ if (var_linkage !=3D BTF_VAR_GLOBAL_ALLOCATED) continue; --=20 2.25.1