The skeleton generated by `bpftool` makes it easy to attach and load bpf
objects as a whole. Some BPF programs are not directly portable across kernel
versions, though, and require some cherry-picking on which programs to
load/attach. The skeleton makes this cherry-picking possible, but not entirely
friendly in some cases.
For example, an useful feature is `attach_with_fallback` so that one
program can be attempted, and fallback programs tried subsequently until
one works (think `tcp_recvmsg` interface changing on kernel 5.19).
Being able to represent a set of probes programatically in a way that is both
descriptive, compile-time validated, runtime efficient and custom library
friendly is quite desirable for application developers. A very simple way to
represent a set of probes is with an array of indices.
This patch creates a couple of enums under the `__cplusplus` section to
represent the program and map indices inside the skeleton object, that can be
used to refer to the proper program/map object.
This is the code generated for the `__cplusplus` section of `profiler.skel.h`:
```
enum map_idxs: size_t {
events = 0,
fentry_readings = 1,
accum_readings = 2,
counts = 3,
rodata = 4
};
enum prog_idxs: size_t {
fentry_XXX = 0,
fexit_XXX = 1
};
static inline struct profiler_bpf *open(const struct bpf_object_open_opts *opts = nullptr);
static inline struct profiler_bpf *open_and_load();
static inline int load(struct profiler_bpf *skel);
static inline int attach(struct profiler_bpf *skel);
static inline void detach(struct profiler_bpf *skel);
static inline void destroy(struct profiler_bpf *skel);
static inline const void *elf_bytes(size_t *sz);
```
---
src/gen.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/src/gen.c b/src/gen.c
index 7070dcf..7e28dc7 100644
--- a/src/gen.c
+++ b/src/gen.c
@@ -1086,6 +1086,38 @@ static int do_skeleton(int argc, char **argv)
\n\
\n\
#ifdef __cplusplus \n\
+ "
+ );
+
+ {
+ size_t i = 0;
+ printf("\tenum map_index: size_t {");
+ bpf_object__for_each_map(map, obj) {
+ if (!get_map_ident(map, ident, sizeof(ident)))
+ continue;
+ if (i) {
+ printf(",");
+ }
+ printf("\n\t\t%s = %lu", ident, i);
+ ++i;
+ }
+ printf("\n\t};\n");
+ }
+ {
+ size_t i = 0;
+ printf("\tenum prog_index: size_t {");
+ bpf_object__for_each_program(prog, obj) {
+ if (i) {
+ printf(",");
+ }
+ printf("\n\t\t%s = %lu", bpf_program__name(prog), i);
+ ++i;
+ }
+ printf("\n\t};\n");
+ }
+
+ codegen("\
+ \n\
static inline struct %1$s *open(const struct bpf_object_open_opts *opts = nullptr);\n\
static inline struct %1$s *open_and_load(); \n\
static inline int load(struct %1$s *skel); \n\
--
2.37.2
