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Commit 6a8a0da4 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Greg Kroah-Hartman
Browse files

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: 351131b5 ("libbpf: add btf_dump API for BTF-to-C conversion")
Reported-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarStanislav Fomichev <sdf@fomichev.me>
Link: https://lore.kernel.org/bpf/20240712224442.282823-1-andrii@kernel.org


Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent f4eee360

tools/lib/bpf/btf_dump.c

+5 −3
Original line number Diff line number Diff line
@@ -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;

			}

tools/testing/selftests/bpf/progs/btf_dump_test_case_multidim.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

tools/testing/selftests/bpf/progs/btf_dump_test_case_syntax.c

+2 −2
Original line number Diff line number Diff line
@@ -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;