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[24.46.218.209]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6f6e39f588asm25725556d6.49.2025.05.10.05.35.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 10 May 2025 05:35:14 -0700 (PDT) From: Lorenz Bauer Date: Sat, 10 May 2025 08:34:56 -0400 Subject: [PATCH bpf-next v4 3/3] libbpf: Use mmap to parse vmlinux BTF from sysfs Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20250510-vmlinux-mmap-v4-3-69e424b2a672@isovalent.com> References: <20250510-vmlinux-mmap-v4-0-69e424b2a672@isovalent.com> In-Reply-To: <20250510-vmlinux-mmap-v4-0-69e424b2a672@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 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. Signed-off-by: Lorenz Bauer --- tools/lib/bpf/btf.c | 85 +++++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 69 insertions(+), 16 deletions(-) diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index f18d7e6a453cd9e5c384487659df04f7efafdf5a..42815a29c0a52a1a7eed2c6b22b9b1754ae01c9a 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; + /* whether raw_data is a (read-only) mmap */ + bool raw_data_is_mmap; + /* BTF object FD, if loaded into kernel */ int fd; @@ -951,6 +955,17 @@ static bool btf_is_modifiable(const struct btf *btf) return (void *)btf->hdr != btf->raw_data; } +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 = false; + } else { + free(btf->raw_data); + } + btf->raw_data = 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)); } -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 = base_btf->hdr->str_len; } - btf->raw_data = malloc(size); - if (!btf->raw_data) { - err = -ENOMEM; - goto done; + if (is_mmap) { + btf->raw_data = (void *)data; + btf->raw_data_is_mmap = true; + } else { + btf->raw_data = malloc(size); + if (!btf->raw_data) { + err = -ENOMEM; + goto done; + } + memcpy(btf->raw_data, data, size); } - memcpy(btf->raw_data, data, size); + btf->raw_size = size; btf->hdr = btf->raw_data; @@ -1083,12 +1104,12 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf) 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)); } 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)); } struct btf_elf_secs { @@ -1209,7 +1230,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, if (secs.btf_base_data) { dist_base_btf = btf_new(secs.btf_base_data->d_buf, secs.btf_base_data->d_size, - NULL); + NULL, false); if (IS_ERR(dist_base_btf)) { err = PTR_ERR(dist_base_btf); dist_base_btf = NULL; @@ -1218,7 +1239,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, } btf = 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 = PTR_ERR(btf); goto done; @@ -1335,7 +1356,7 @@ static struct btf *btf_parse_raw(const char *path, struct btf *base_btf) } /* finally parse BTF data */ - btf = btf_new(data, sz, base_btf); + btf = btf_new(data, sz, base_btf, false); err_out: free(data); @@ -1354,6 +1375,36 @@ struct btf *btf__parse_raw_split(const char *path, struct btf *base_btf) return libbpf_ptr(btf_parse_raw(path, base_btf)); } +static struct btf *btf_parse_raw_mmap(const char *path, struct btf *base_btf) +{ + struct stat st; + void *data; + struct btf *btf; + int fd, err; + + fd = open(path, O_RDONLY); + if (fd < 0) + return libbpf_err_ptr(-errno); + + if (fstat(fd, &st) < 0) { + err = -errno; + close(fd); + return libbpf_err_ptr(err); + } + + data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0); + close(fd); + + if (data == MAP_FAILED) + return NULL; + + btf = 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, struct btf_ext **btf_ext) { struct btf *btf; @@ -1618,7 +1669,7 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf) goto exit_free; } - btf = btf_new(ptr, btf_info.btf_size, base_btf); + btf = btf_new(ptr, btf_info.btf_size, base_btf, false); exit_free: free(ptr); @@ -1659,8 +1710,7 @@ struct btf *btf__load_from_kernel_by_id(__u32 id) static void btf_invalidate_raw_data(struct btf *btf) { if (btf->raw_data) { - free(btf->raw_data); - btf->raw_data = NULL; + btf_free_raw_data(btf); } if (btf->raw_data_swapped) { free(btf->raw_data_swapped); @@ -5331,7 +5381,10 @@ struct btf *btf__load_vmlinux_btf(void) pr_warn("kernel BTF is missing at '%s', was CONFIG_DEBUG_INFO_BTF enabled?\n", sysfs_btf_path); } else { - btf = btf__parse(sysfs_btf_path, NULL); + btf = btf_parse_raw_mmap(sysfs_btf_path, NULL); + if (IS_ERR_OR_NULL(btf)) + btf = btf__parse(sysfs_btf_path, NULL); + if (!btf) { err = -errno; pr_warn("failed to read kernel BTF from '%s': %s\n",