On Fri, Nov 09, 2018 at 08:21:41AM -0800, Stanislav Fomichev wrote:
[ ... ]
> @@ -1918,23 +2160,20 @@ void *bpf_object__priv(struct bpf_object *obj)
> }
>
> static struct bpf_program *
> -__bpf_program__next(struct bpf_program *prev, struct bpf_object *obj)
> +__bpf_program__iter(struct bpf_program *p, struct bpf_object *obj, int i)
> {
> - size_t idx;
> + ssize_t idx;
>
> if (!obj->programs)
> return NULL;
> - /* First handler */
> - if (prev == NULL)
> - return &obj->programs[0];
>
> - if (prev->obj != obj) {
> + if (p->obj != obj) {
> pr_warning("error: program handler doesn't match object\n");
> return NULL;
> }
>
> - idx = (prev - obj->programs) + 1;
> - if (idx >= obj->nr_programs)
> + idx = (p - obj->programs) + i;
> + if (idx >= obj->nr_programs || idx < 0)
> return NULL;
> return &obj->programs[idx];
> }
> @@ -1944,8 +2183,29 @@ bpf_program__next(struct bpf_program *prev, struct
> bpf_object *obj)
> {
> struct bpf_program *prog = prev;
>
> + if (prev == NULL)
> + return obj->programs;
> +
This patch breaks the behavior introduced in
commit eac7d84519a3 ("tools: libbpf: don't return '.text' as a program for
multi-function programs"):
"Make bpf_program__next() skip over '.text' section if object file
has pseudo calls. The '.text' section is hardly a program in that
case, it's more of a storage for code of functions other than main."
For example, the userspace could have been doing:
prog = bpf_program__next(NULL, obj);
bpf_program__set_type(prog, BPF_PROG_TYPE_TRACEPOINT);
bpf_object__load(obj);
For the bpf_prog.o that has pseudo calls, after this patch in bpf-next,
the prog returned by bpf_program__next() could be in ".text" instead of
the main bpf program. The next bpf_program__set_type() has
no effect to the main program. The following bpf_object__load()
will catch user in surprise with the main bpf prog in
the wrong BPF_PROG_TYPE.
> do {
> - prog = __bpf_program__next(prog, obj);
> + prog = __bpf_program__iter(prog, obj, 1);
> + } while (prog && bpf_program__is_function_storage(prog, obj));
> +
> + return prog;
> +}
> +
> +struct bpf_program *
> +bpf_program__prev(struct bpf_program *next, struct bpf_object *obj)
> +{
> + struct bpf_program *prog = next;
> +
> + if (next == NULL) {
> + if (!obj->nr_programs)
> + return NULL;
> + return obj->programs + obj->nr_programs - 1;
> + }
> +
> + do {
> + prog = __bpf_program__iter(prog, obj, -1);
> } while (prog && bpf_program__is_function_storage(prog, obj));
>
> return prog;
