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[2001:8b0:7a5a:26ff::600]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a099b17017sm1742342f8f.92.2025.05.02.03.20.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 May 2025 03:20:34 -0700 (PDT) From: Lorenz Bauer Date: Fri, 02 May 2025 11:20:07 +0100 Subject: [PATCH bpf-next v2 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: <20250502-vmlinux-mmap-v2-3-95c271434519@isovalent.com> References: <20250502-vmlinux-mmap-v2-0-95c271434519@isovalent.com> In-Reply-To: <20250502-vmlinux-mmap-v2-0-95c271434519@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 | 82 ++++++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 71 insertions(+), 11 deletions(-) diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index b7513d4cce55b263310c341bc254df6364e829d9..7fec41a2dc617c9d388f9ab10d9850ef759c74d9 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_no_copy(void *data, __u32 size, struct btf *base_btf) { struct btf *btf; int err; @@ -1050,12 +1065,7 @@ 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; - } - memcpy(btf->raw_data, data, size); + btf->raw_data = data; btf->raw_size = size; btf->hdr = btf->raw_data; @@ -1081,6 +1091,24 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf) return btf; } +static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf) +{ + struct btf *btf; + void *raw_data; + + raw_data = malloc(size); + if (!raw_data) + return ERR_PTR(-ENOMEM); + + memcpy(raw_data, data, size); + + btf = btf_new_no_copy(raw_data, size, base_btf); + if (IS_ERR(btf)) + free(raw_data); + + return btf; +} + struct btf *btf__new(const void *data, __u32 size) { return libbpf_ptr(btf_new(data, size, NULL)); @@ -1659,8 +1687,7 @@ 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); @@ -5290,7 +5317,40 @@ 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); + struct stat st; + void *data = NULL; + int fd; + + fd = open(sysfs_btf_path, O_RDONLY); + if (fd < 0) { + err = -errno; + pr_warn("failed to open kernel BTF at '%s': %s\n", + sysfs_btf_path, errstr(err)); + return libbpf_err_ptr(err); + } + + if (fstat(fd, &st) < 0) { + err = -errno; + pr_warn("failed to stat kernel BTF at '%s': %s\n", + sysfs_btf_path, errstr(err)); + 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) { + btf = libbpf_ptr(btf_new_no_copy(data, st.st_size, NULL)); + if (!btf) + munmap(data, st.st_size); + else + btf->raw_data_is_mmap = true; + } else { + pr_debug("reading kernel BTF via file-based fallback\n"); + btf = btf__parse(sysfs_btf_path, NULL); + } + if (!btf) { err = -errno; pr_warn("failed to read kernel BTF from '%s': %s\n",