This is a note to let you know that I've just added the patch titled
libbpf: Fix no-args func prototype BTF dumping syntax
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
libbpf-fix-no-args-func-prototype-btf-dumping-syntax.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 37e55d54112c1b9dde67859ba9e4f080de1ab905
Author: Andrii Nakryiko <andrii@xxxxxxxxxx>
Date: Fri Jul 12 15:44:42 2024 -0700
libbpf: Fix no-args func prototype BTF dumping syntax
[ Upstream commit 189f1a976e426011e6a5588f1d3ceedf71fe2965 ]
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@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20240712224442.282823-1-andrii@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index a1176a9e8430a..1391f6c292054 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -1302,10 +1302,12 @@ 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;
}
diff --git a/tools/testing/selftests/bpf/progs/btf_dump_test_case_multidim.c b/tools/testing/selftests/bpf/progs/btf_dump_test_case_multidim.c
index ba97165bdb282..a657651eba523 100644
--- a/tools/testing/selftests/bpf/progs/btf_dump_test_case_multidim.c
+++ b/tools/testing/selftests/bpf/progs/btf_dump_test_case_multidim.c
@@ -14,9 +14,9 @@ typedef int *ptr_arr_t[6];
typedef int *ptr_multiarr_t[7][8][9][10];
-typedef int * (*fn_ptr_arr_t[11])();
+typedef int * (*fn_ptr_arr_t[11])(void);
-typedef int * (*fn_ptr_multiarr_t[12][13])();
+typedef int * (*fn_ptr_multiarr_t[12][13])(void);
struct root_struct {
arr_t _1;
diff --git a/tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c b/tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c
index 0620580a5c16c..1fcca43ab342d 100644
--- a/tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c
+++ b/tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c
@@ -67,7 +67,7 @@ typedef void (*printf_fn_t)(const char *, ...);
* `int -> char *` function and returns pointer to a char. Equivalent:
* typedef char * (*fn_input_t)(int);
* typedef char * (*fn_output_outer_t)(fn_input_t);
- * typedef const fn_output_outer_t (* fn_output_inner_t)();
+ * typedef const fn_output_outer_t (* fn_output_inner_t)(void);
* typedef const fn_output_inner_t fn_ptr_arr2_t[5];
*/
/* ----- START-EXPECTED-OUTPUT ----- */
@@ -94,7 +94,7 @@ typedef void (* (*signal_t)(int, void (*)(int)))(int);
typedef char * (*fn_ptr_arr1_t[10])(int **);
-typedef char * (* (* const fn_ptr_arr2_t[5])())(char * (*)(int));
+typedef char * (* (* const fn_ptr_arr2_t[5])(void))(char * (*)(int));
struct struct_w_typedefs {
int_t a;
