libbpf: Fail early when loading programs with unspecified type

Before this patch, a program with unspecified type
(BPF_PROG_TYPE_UNSPEC) would be passed to the BPF syscall, only to have
the kernel reject it with an opaque invalid argument error. This patch
makes libbpf reject such programs with a nicer error message - in
particular libbpf now tries to diagnose bad ELF section names at both
open time and load time.

Signed-off-by: Andrei Matei <andreimatei1@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20201203043410.59699-1-andreimatei1@gmail.com

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 3130341..d6f4553 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6629,6 +6629,16 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
        char *log_buf = NULL;
        int btf_fd, ret;
 
+       if (prog->type == BPF_PROG_TYPE_UNSPEC) {
+               /*
+                * The program type must be set.  Most likely we couldn't find a proper
+                * section definition at load time, and thus we didn't infer the type.
+                */
+               pr_warn("prog '%s': missing BPF prog type, check ELF section name '%s'\n",
+                       prog->name, prog->sec_name);
+               return -EINVAL;
+       }
+
        if (!insns || !insns_cnt)
                return -EINVAL;
 
@@ -6920,9 +6930,12 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
 
        bpf_object__for_each_program(prog, obj) {
                prog->sec_def = find_sec_def(prog->sec_name);
-               if (!prog->sec_def)
+               if (!prog->sec_def) {
                        /* couldn't guess, but user might manually specify */
+                       pr_debug("prog '%s': unrecognized ELF section name '%s'\n",
+                               prog->name, prog->sec_name);
                        continue;
+               }
 
                if (prog->sec_def->is_sleepable)
                        prog->prog_flags |= BPF_F_SLEEPABLE;