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authorAndrii Nakryiko <andrii@kernel.org>2021-10-26 01:45:29 +0300
committerAlexei Starovoitov <ast@kernel.org>2021-10-26 04:37:21 +0300
commit65a7fa2e4e5381d205d3b0098da0fc8471fbbfb6 (patch)
tree0b451016988454b1ebeec6ca9ec09d40b3c67908 /tools/lib
parentde5d0dcef602de39070c31c7e56c58249c56ba37 (diff)
downloadlinux-65a7fa2e4e5381d205d3b0098da0fc8471fbbfb6.tar.xz
libbpf: Add ability to fetch bpf_program's underlying instructions
Add APIs providing read-only access to bpf_program BPF instructions ([0]). This is useful for diagnostics purposes, but it also allows a cleaner support for cloning BPF programs after libbpf did all the FD resolution and CO-RE relocations, subprog instructions appending, etc. Currently, cloning BPF program is possible only through hijacking a half-broken bpf_program__set_prep() API, which doesn't really work well for anything but most primitive programs. For instance, set_prep() API doesn't allow adjusting BPF program load parameters which are necessary for loading fentry/fexit BPF programs (the case where BPF program cloning is a necessity if doing some sort of mass-attachment functionality). Given bpf_program__set_prep() API is set to be deprecated, having a cleaner alternative is a must. libbpf internally already keeps track of linear array of struct bpf_insn, so it's not hard to expose it. The only gotcha is that libbpf previously freed instructions array during bpf_object load time, which would make this API much less useful overall, because in between bpf_object__open() and bpf_object__load() a lot of changes to instructions are done by libbpf. So this patch makes libbpf hold onto prog->insns array even after BPF program loading. I think this is a small price for added functionality and improved introspection of BPF program code. See retsnoop PR ([1]) for how it can be used in practice and code savings compared to relying on bpf_program__set_prep(). [0] Closes: https://github.com/libbpf/libbpf/issues/298 [1] https://github.com/anakryiko/retsnoop/pull/1 Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211025224531.1088894-3-andrii@kernel.org
Diffstat (limited to 'tools/lib')
-rw-r--r--tools/lib/bpf/libbpf.c12
-rw-r--r--tools/lib/bpf/libbpf.h36
-rw-r--r--tools/lib/bpf/libbpf.map2
3 files changed, 46 insertions, 4 deletions
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e27a249d46fb..dc86ad24dfcb 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6653,8 +6653,6 @@ int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver)
out:
if (err)
pr_warn("failed to load program '%s'\n", prog->name);
- zfree(&prog->insns);
- prog->insns_cnt = 0;
return libbpf_err(err);
}
@@ -8143,6 +8141,16 @@ size_t bpf_program__size(const struct bpf_program *prog)
return prog->insns_cnt * BPF_INSN_SZ;
}
+const struct bpf_insn *bpf_program__insns(const struct bpf_program *prog)
+{
+ return prog->insns;
+}
+
+size_t bpf_program__insn_cnt(const struct bpf_program *prog)
+{
+ return prog->insns_cnt;
+}
+
int bpf_program__set_prep(struct bpf_program *prog, int nr_instances,
bpf_program_prep_t prep)
{
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 89ca9c83ed4e..c6bcc5b98906 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -226,6 +226,40 @@ LIBBPF_API int bpf_program__set_autoload(struct bpf_program *prog, bool autoload
/* returns program size in bytes */
LIBBPF_API size_t bpf_program__size(const struct bpf_program *prog);
+struct bpf_insn;
+
+/**
+ * @brief **bpf_program__insns()** gives read-only access to BPF program's
+ * underlying BPF instructions.
+ * @param prog BPF program for which to return instructions
+ * @return a pointer to an array of BPF instructions that belong to the
+ * specified BPF program
+ *
+ * Returned pointer is always valid and not NULL. Number of `struct bpf_insn`
+ * pointed to can be fetched using **bpf_program__insn_cnt()** API.
+ *
+ * Keep in mind, libbpf can modify and append/delete BPF program's
+ * instructions as it processes BPF object file and prepares everything for
+ * uploading into the kernel. So depending on the point in BPF object
+ * lifetime, **bpf_program__insns()** can return different sets of
+ * instructions. As an example, during BPF object load phase BPF program
+ * instructions will be CO-RE-relocated, BPF subprograms instructions will be
+ * appended, ldimm64 instructions will have FDs embedded, etc. So instructions
+ * returned before **bpf_object__load()** and after it might be quite
+ * different.
+ */
+LIBBPF_API const struct bpf_insn *bpf_program__insns(const struct bpf_program *prog);
+/**
+ * @brief **bpf_program__insn_cnt()** returns number of `struct bpf_insn`'s
+ * that form specified BPF program.
+ * @param prog BPF program for which to return number of BPF instructions
+ *
+ * See **bpf_program__insns()** documentation for notes on how libbpf can
+ * change instructions and their count during different phases of
+ * **bpf_object** lifetime.
+ */
+LIBBPF_API size_t bpf_program__insn_cnt(const struct bpf_program *prog);
+
LIBBPF_API int bpf_program__load(struct bpf_program *prog, char *license,
__u32 kern_version);
LIBBPF_API int bpf_program__fd(const struct bpf_program *prog);
@@ -365,8 +399,6 @@ LIBBPF_API struct bpf_link *
bpf_program__attach_iter(const struct bpf_program *prog,
const struct bpf_iter_attach_opts *opts);
-struct bpf_insn;
-
/*
* Libbpf allows callers to adjust BPF programs before being loaded
* into kernel. One program in an object file can be transformed into
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 116964a29e44..15239c05659c 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -393,6 +393,8 @@ LIBBPF_0.6.0 {
bpf_object__next_program;
bpf_object__prev_map;
bpf_object__prev_program;
+ bpf_program__insn_cnt;
+ bpf_program__insns;
btf__add_btf;
btf__add_decl_tag;
btf__raw_data;