From 6a8a0da4d84a4018c210c043d4331945a524ba29 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Fri, 12 Jul 2024 15:44:42 -0700 Subject: [PATCH] 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 Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Acked-by: Stanislav Fomichev Link: https://lore.kernel.org/bpf/20240712224442.282823-1-andrii@kernel.org Signed-off-by: Sasha Levin --- tools/lib/bpf/btf_dump.c | 8 +++++--- .../selftests/bpf/progs/btf_dump_test_case_multidim.c | 4 ++-- .../selftests/bpf/progs/btf_dump_test_case_syntax.c | 4 ++-- 3 files changed, 9 insertions(+), 7 deletions(-) diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index a1176a9e8430..1391f6c29205 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 ba97165bdb28..a657651eba52 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 0620580a5c16..1fcca43ab342 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;