From: Bryce Kahle <bryce.kahle@xxxxxxxxxxxxx> Enables a user to generate minimized kernel module BTF. If an eBPF program probes a function within a kernel module or uses types that come from a kernel module, split BTF is required. The split module BTF contains only the BTF types that are unique to the module. It will reference the base/vmlinux BTF types and always starts its type IDs at X+1 where X is the largest type ID in the base BTF. Minimization allows a user to ship only the types necessary to do relocations for the program(s) in the provided eBPF object file(s). A minimized module BTF will still not contain vmlinux BTF types, so you should always minimize the vmlinux file first, and then minimize the kernel module file. Example: bpftool gen min_core_btf vmlinux.btf vm-min.btf prog.bpf.o bpftool -B vm-min.btf gen min_core_btf mod.btf mod-min.btf prog.bpf.o v3->v4: - address style nit about start_id initialization - rename base to src_base_btf (base_btf is a global var) - copy src_base_btf so new BTF is not modifying original vmlinux BTF Signed-off-by: Bryce Kahle <bryce.kahle@xxxxxxxxxxxxx> --- .../bpf/bpftool/Documentation/bpftool-gen.rst | 18 ++++++++++- tools/bpf/bpftool/gen.c | 32 +++++++++++++++---- 2 files changed, 42 insertions(+), 8 deletions(-) diff --git a/tools/bpf/bpftool/Documentation/bpftool-gen.rst b/tools/bpf/bpftool/Documentation/bpftool-gen.rst index 5006e724d..e067d3b05 100644 --- a/tools/bpf/bpftool/Documentation/bpftool-gen.rst +++ b/tools/bpf/bpftool/Documentation/bpftool-gen.rst @@ -16,7 +16,7 @@ SYNOPSIS **bpftool** [*OPTIONS*] **gen** *COMMAND* - *OPTIONS* := { |COMMON_OPTIONS| | { **-L** | **--use-loader** } } + *OPTIONS* := { |COMMON_OPTIONS| | { **-B** | **--base-btf** } | { **-L** | **--use-loader** } } *COMMAND* := { **object** | **skeleton** | **help** } @@ -202,6 +202,14 @@ OPTIONS ======= .. include:: common_options.rst + -B, --base-btf *FILE* + Pass a base BTF object. Base BTF objects are typically used + with BTF objects for kernel modules. To avoid duplicating + all kernel symbols required by modules, BTF objects for + modules are "split", they are built incrementally on top of + the kernel (vmlinux) BTF object. So the base BTF reference + should usually point to the kernel BTF. + -L, --use-loader For skeletons, generate a "light" skeleton (also known as "loader" skeleton). A light skeleton contains a loader eBPF program. It does @@ -444,3 +452,11 @@ ones given to min_core_btf. obj = bpf_object__open_file("one.bpf.o", &opts); ... + +Kernel module BTF may also be minimized by using the -B option: + +**$ bpftool -B 5.4.0-smaller.btf gen min_core_btf 5.4.0-module.btf 5.4.0-module-smaller.btf one.bpf.o** + +A minimized module BTF will still not contain vmlinux BTF types, so you +should always minimize the vmlinux file first, and then minimize the +kernel module file. diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c index ee3ce2b80..57691f766 100644 --- a/tools/bpf/bpftool/gen.c +++ b/tools/bpf/bpftool/gen.c @@ -1630,6 +1630,7 @@ static int do_help(int argc, char **argv) " %1$s %2$s help\n" "\n" " " HELP_SPEC_OPTIONS " |\n" + " {-B|--base-btf} |\n" " {-L|--use-loader} }\n" "", bin_name, "gen"); @@ -1695,14 +1696,14 @@ btfgen_new_info(const char *targ_btf_path) if (!info) return NULL; - info->src_btf = btf__parse(targ_btf_path, NULL); + info->src_btf = btf__parse_split(targ_btf_path, base_btf); if (!info->src_btf) { err = -errno; p_err("failed parsing '%s' BTF file: %s", targ_btf_path, strerror(errno)); goto err_out; } - info->marked_btf = btf__parse(targ_btf_path, NULL); + info->marked_btf = btf__parse_split(targ_btf_path, base_btf); if (!info->marked_btf) { err = -errno; p_err("failed parsing '%s' BTF file: %s", targ_btf_path, strerror(errno)); @@ -2139,12 +2140,29 @@ static int btfgen_remap_id(__u32 *type_id, void *ctx) /* Generate BTF from relocation information previously recorded */ static struct btf *btfgen_get_btf(struct btfgen_info *info) { - struct btf *btf_new = NULL; + struct btf *btf_new = NULL, *src_base_btf_new = NULL; unsigned int *ids = NULL; + const struct btf *src_base_btf; unsigned int i, n = btf__type_cnt(info->marked_btf); - int err = 0; + int start_id, err = 0; + + src_base_btf = btf__base_btf(info->src_btf); + start_id = src_base_btf ? btf__type_cnt(src_base_btf) : 1; - btf_new = btf__new_empty(); + /* clone BTF to sanitize a copy and leave the original intact */ + if (src_base_btf) { + const void *raw_data; + __u32 sz; + + raw_data = btf__raw_data(src_base_btf, &sz); + src_base_btf_new = btf__new(raw_data, sz); + if (!src_base_btf_new) { + err = -errno; + goto err_out; + } + } + + btf_new = btf__new_empty_split(src_base_btf_new); if (!btf_new) { err = -errno; goto err_out; @@ -2157,7 +2175,7 @@ static struct btf *btfgen_get_btf(struct btfgen_info *info) } /* first pass: add all marked types to btf_new and add their new ids to the ids map */ - for (i = 1; i < n; i++) { + for (i = start_id; i < n; i++) { const struct btf_type *cloned_type, *type; const char *name; int new_id; @@ -2213,7 +2231,7 @@ static struct btf *btfgen_get_btf(struct btfgen_info *info) } /* second pass: fix up type ids */ - for (i = 1; i < btf__type_cnt(btf_new); i++) { + for (i = start_id; i < btf__type_cnt(btf_new); i++) { struct btf_type *btf_type = (struct btf_type *) btf__type_by_id(btf_new, i); err = btf_type_visit_type_ids(btf_type, btfgen_remap_id, ids); -- 2.25.1