On Wed, Aug 27, 2025 at 6:05 AM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote: > > The verifier requires that pointers returned by bpf_obj_new_impl() are > either dropped or stored in a map. Therefore programs that do not use > its return values will fail to load. Make the compiler point out these > issues. Adjust selftests that check that the verifier does indeed spot > these bugs. > > Link: https://lore.kernel.org/bpf/CAADnVQL6Q+QRv3_JwEd26biwGpFYcwD_=BjBJWLAtpgOP9CKRw@xxxxxxxxxxxxxx/ > Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx> > Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx> > --- > tools/lib/bpf/bpf_helpers.h | 4 ++++ > tools/testing/selftests/bpf/bpf_experimental.h | 2 +- > tools/testing/selftests/bpf/progs/linked_list_fail.c | 8 ++++---- > 3 files changed, 9 insertions(+), 5 deletions(-) > > diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h > index 80c028540656..e1496a328e3f 100644 > --- a/tools/lib/bpf/bpf_helpers.h > +++ b/tools/lib/bpf/bpf_helpers.h > @@ -69,6 +69,10 @@ > */ > #define __hidden __attribute__((visibility("hidden"))) > > +#ifndef __must_check > +#define __must_check __attribute__((__warn_unused_result__)) > +#endif > + do we need to add this to libbpf UAPI? let's put it in selftests header somewhere instead? > /* When utilizing vmlinux.h with BPF CO-RE, user BPF programs can't include > * any system-level headers (such as stddef.h, linux/version.h, etc), and > * commonly-used macros like NULL and KERNEL_VERSION aren't available through > diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h > index da7e230f2781..e5ef4792da42 100644 > --- a/tools/testing/selftests/bpf/bpf_experimental.h > +++ b/tools/testing/selftests/bpf/bpf_experimental.h > @@ -20,7 +20,7 @@ > * A pointer to an object of the type corresponding to the passed in > * 'local_type_id', or NULL on failure. > */ > -extern void *bpf_obj_new_impl(__u64 local_type_id, void *meta) __ksym; > +extern __must_check void *bpf_obj_new_impl(__u64 local_type_id, void *meta) __ksym; bpf_obj_new_impl will generally come from vmlinux.h nowadays, and that one won't have __must_check annotation, is that a problem? > > /* Convenience macro to wrap over bpf_obj_new_impl */ > #define bpf_obj_new(type) ((type *)bpf_obj_new_impl(bpf_core_type_id_local(type), NULL)) > diff --git a/tools/testing/selftests/bpf/progs/linked_list_fail.c b/tools/testing/selftests/bpf/progs/linked_list_fail.c > index 6438982b928b..84883f04d58b 100644 > --- a/tools/testing/selftests/bpf/progs/linked_list_fail.c > +++ b/tools/testing/selftests/bpf/progs/linked_list_fail.c > @@ -212,14 +212,14 @@ int map_compat_raw_tp_w(void *ctx) > SEC("?tc") > int obj_type_id_oor(void *ctx) > { > - bpf_obj_new_impl(~0UL, NULL); > + (void)bpf_obj_new_impl(~0UL, NULL); > return 0; > } > > SEC("?tc") > int obj_new_no_composite(void *ctx) > { > - bpf_obj_new_impl(bpf_core_type_id_local(int), (void *)42); > + (void)bpf_obj_new_impl(bpf_core_type_id_local(int), (void *)42); > return 0; > } > > @@ -227,7 +227,7 @@ SEC("?tc") > int obj_new_no_struct(void *ctx) > { > > - bpf_obj_new(union { int data; unsigned udata; }); > + (void)bpf_obj_new(union { int data; unsigned udata; }); > return 0; > } > > @@ -252,7 +252,7 @@ int new_null_ret(void *ctx) > SEC("?tc") > int obj_new_acq(void *ctx) > { > - bpf_obj_new(struct foo); > + (void)bpf_obj_new(struct foo); > return 0; > } > > -- > 2.50.1 >
