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libbpf: Fix no-args func prototype BTF dumping syntax

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For all these years libbpf's BTF dumper has been emitting not strictly
valid syntax for function prototypes that have no input arguments.

Instead of `int (*blah)()` we should emit `int (*blah)(void)`.

This is not normally a problem, but it manifests when we get kfuncs in
vmlinux.h that have no input arguments. Due to compiler internal
specifics, we get no BTF information for such kfuncs, if they are not
declared with proper `(void)`.

The fix is trivial. We also need to adjust a few ancient tests that
happily assumed `()` is correct.

Fixes: 351131b51c7a ("libbpf: add btf_dump API for BTF-to-C conversion")
Reported-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://lore.kernel.org/bpf/20240712224442.282823-1-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko
2024-07-12 15:44:42 -07:00
committed by Andrii Nakryiko
parent 86fc78bd2b
commit 205e86de8b
1 changed files with 5 additions and 3 deletions
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8
src/btf_dump.c
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@@ -1559,10 +1559,12 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
* Clang for BPF target generates func_proto with no
* args as a func_proto with a single void arg (e.g.,
* `int (*f)(void)` vs just `int (*f)()`). We are
* going to pretend there are no args for such case.
* going to emit valid empty args (void) syntax for
* such case. Similarly and conveniently, valid
* no args case can be special-cased here as well.
*/
if (vlen == 1 && p->type == 0) {
btf_dump_printf(d, ")");
if (vlen == 0 || (vlen == 1 && p->type == 0)) {
btf_dump_printf(d, "void)");
return;
}