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[2001:8b0:7a5a:26ff::600]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a35ca5a8cfsm16538095f8f.37.2025.05.20.06.01.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 May 2025 06:01:41 -0700 (PDT) From: Lorenz Bauer Date: Tue, 20 May 2025 14:01:19 +0100 Subject: [PATCH bpf-next v5 3/3] libbpf: Use mmap to parse vmlinux BTF from sysfs Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250520-vmlinux-mmap-v5-3-e8c941acc414@isovalent.com> References: <20250520-vmlinux-mmap-v5-0-e8c941acc414@isovalent.com> In-Reply-To: <20250520-vmlinux-mmap-v5-0-e8c941acc414@isovalent.com> To: Arnd Bergmann , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Mykola Lysenko , Shuah Khan Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, Lorenz Bauer , Alan Maguire X-Mailer: b4 0.14.2 Teach libbpf to use mmap when parsing vmlinux BTF from /sys. We don't apply this to fall-back paths on the regular file system because there is no way to ensure that modifications underlying the MAP_PRIVATE mapping are not visible to the process. Acked-by: Andrii Nakryiko Tested-by: Alan Maguire Signed-off-by: Lorenz Bauer --- tools/lib/bpf/btf.c | 89 ++++++++++++++++++++++++++++++++++++++++++-------= ---- 1 file changed, 71 insertions(+), 18 deletions(-) diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index f18d7e6a453cd9e5c384487659df04f7efafdf5a..3b98ac40bbd66c4fa688f967f93= 70b5c92610ba0 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -120,6 +121,9 @@ struct btf { /* whether base_btf should be freed in btf_free for this instance */ bool owns_base; =20 + /* whether raw_data is a (read-only) mmap */ + bool raw_data_is_mmap; + /* BTF object FD, if loaded into kernel */ int fd; =20 @@ -951,6 +955,17 @@ static bool btf_is_modifiable(const struct btf *btf) return (void *)btf->hdr !=3D btf->raw_data; } =20 +static void btf_free_raw_data(struct btf *btf) +{ + if (btf->raw_data_is_mmap) { + munmap(btf->raw_data, btf->raw_size); + btf->raw_data_is_mmap =3D false; + } else { + free(btf->raw_data); + } + btf->raw_data =3D NULL; +} + void btf__free(struct btf *btf) { if (IS_ERR_OR_NULL(btf)) @@ -970,7 +985,7 @@ void btf__free(struct btf *btf) free(btf->types_data); strset__free(btf->strs_set); } - free(btf->raw_data); + btf_free_raw_data(btf); free(btf->raw_data_swapped); free(btf->type_offs); if (btf->owns_base) @@ -1030,7 +1045,7 @@ struct btf *btf__new_empty_split(struct btf *base_btf) return libbpf_ptr(btf_new_empty(base_btf)); } =20 -static struct btf *btf_new(const void *data, __u32 size, struct btf *base_= btf) +static struct btf *btf_new(const void *data, __u32 size, struct btf *base_= btf, bool is_mmap) { struct btf *btf; int err; @@ -1050,12 +1065,18 @@ static struct btf *btf_new(const void *data, __u32 = size, struct btf *base_btf) btf->start_str_off =3D base_btf->hdr->str_len; } =20 - btf->raw_data =3D malloc(size); - if (!btf->raw_data) { - err =3D -ENOMEM; - goto done; + if (is_mmap) { + btf->raw_data =3D (void *)data; + btf->raw_data_is_mmap =3D true; + } else { + btf->raw_data =3D malloc(size); + if (!btf->raw_data) { + err =3D -ENOMEM; + goto done; + } + memcpy(btf->raw_data, data, size); } - memcpy(btf->raw_data, data, size); + btf->raw_size =3D size; =20 btf->hdr =3D btf->raw_data; @@ -1083,12 +1104,12 @@ static struct btf *btf_new(const void *data, __u32 = size, struct btf *base_btf) =20 struct btf *btf__new(const void *data, __u32 size) { - return libbpf_ptr(btf_new(data, size, NULL)); + return libbpf_ptr(btf_new(data, size, NULL, false)); } =20 struct btf *btf__new_split(const void *data, __u32 size, struct btf *base_= btf) { - return libbpf_ptr(btf_new(data, size, base_btf)); + return libbpf_ptr(btf_new(data, size, base_btf, false)); } =20 struct btf_elf_secs { @@ -1209,7 +1230,7 @@ static struct btf *btf_parse_elf(const char *path, st= ruct btf *base_btf, =20 if (secs.btf_base_data) { dist_base_btf =3D btf_new(secs.btf_base_data->d_buf, secs.btf_base_data-= >d_size, - NULL); + NULL, false); if (IS_ERR(dist_base_btf)) { err =3D PTR_ERR(dist_base_btf); dist_base_btf =3D NULL; @@ -1218,7 +1239,7 @@ static struct btf *btf_parse_elf(const char *path, st= ruct btf *base_btf, } =20 btf =3D btf_new(secs.btf_data->d_buf, secs.btf_data->d_size, - dist_base_btf ?: base_btf); + dist_base_btf ?: base_btf, false); if (IS_ERR(btf)) { err =3D PTR_ERR(btf); goto done; @@ -1335,7 +1356,7 @@ static struct btf *btf_parse_raw(const char *path, st= ruct btf *base_btf) } =20 /* finally parse BTF data */ - btf =3D btf_new(data, sz, base_btf); + btf =3D btf_new(data, sz, base_btf, false); =20 err_out: free(data); @@ -1354,6 +1375,37 @@ struct btf *btf__parse_raw_split(const char *path, s= truct btf *base_btf) return libbpf_ptr(btf_parse_raw(path, base_btf)); } =20 +static struct btf *btf_parse_raw_mmap(const char *path, struct btf *base_b= tf) +{ + struct stat st; + void *data; + struct btf *btf; + int fd, err; + + fd =3D open(path, O_RDONLY); + if (fd < 0) + return libbpf_err_ptr(-errno); + + if (fstat(fd, &st) < 0) { + err =3D -errno; + close(fd); + return libbpf_err_ptr(err); + } + + data =3D mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0); + err =3D -errno; + close(fd); + + if (data =3D=3D MAP_FAILED) + return libbpf_err_ptr(err); + + btf =3D btf_new(data, st.st_size, base_btf, true); + if (IS_ERR(btf)) + munmap(data, st.st_size); + + return btf; +} + static struct btf *btf_parse(const char *path, struct btf *base_btf, struc= t btf_ext **btf_ext) { struct btf *btf; @@ -1618,7 +1670,7 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *b= ase_btf) goto exit_free; } =20 - btf =3D btf_new(ptr, btf_info.btf_size, base_btf); + btf =3D btf_new(ptr, btf_info.btf_size, base_btf, false); =20 exit_free: free(ptr); @@ -1658,10 +1710,8 @@ struct btf *btf__load_from_kernel_by_id(__u32 id) =20 static void btf_invalidate_raw_data(struct btf *btf) { - if (btf->raw_data) { - free(btf->raw_data); - btf->raw_data =3D NULL; - } + if (btf->raw_data) + btf_free_raw_data(btf); if (btf->raw_data_swapped) { free(btf->raw_data_swapped); btf->raw_data_swapped =3D NULL; @@ -5331,7 +5381,10 @@ struct btf *btf__load_vmlinux_btf(void) pr_warn("kernel BTF is missing at '%s', was CONFIG_DEBUG_INFO_BTF enable= d?\n", sysfs_btf_path); } else { - btf =3D btf__parse(sysfs_btf_path, NULL); + btf =3D btf_parse_raw_mmap(sysfs_btf_path, NULL); + if (IS_ERR(btf)) + btf =3D btf__parse(sysfs_btf_path, NULL); + if (!btf) { err =3D -errno; pr_warn("failed to read kernel BTF from '%s': %s\n", --=20 2.49.0