5.4-stable review patch. If anyone has any objections, please let me know.
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From: Andrii Nakryiko andrii@kernel.org
[ 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@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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 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;