libbpf: fix sym_is_subprog() logic for weak global subprogs

sym_is_subprog() is incorrectly rejecting relocations against *weak*
global subprogs. Fix that by realizing that STB_WEAK is also a global
function.

While it seems like verifier doesn't support taking an address of
non-static subprog right now, it's still best to fix support for it on
libbpf side, otherwise users will get a very confusing error during BPF
skeleton generation or static linking due to misinterpreted relocation:

  libbpf: prog 'handle_tp': bad map relo against 'foo' in section '.text'
  Error: failed to open BPF object file: Relocation failed

It's clearly not a map relocation, but is treated and reported as such
without this fix.

Fixes: 53eddb5e04ac ("libbpf: Support subprog address relocation")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20241009011554.880168-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 712b95e8891bd2b97887ff9c39856495392cdc7e..05ad264ff09bf1d5d7616efc0cf0239522d7ef8c 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4013,7 +4013,7 @@ static bool sym_is_subprog(const Elf64_Sym *sym, int text_shndx)
                return true;
 
        /* global function */
-       return bind == STB_GLOBAL && type == STT_FUNC;
+       return (bind == STB_GLOBAL || bind == STB_WEAK) && type == STT_FUNC;
 }
 
 static int find_extern_btf_id(const struct btf *btf, const char *ext_name)