On Wed, Aug 27, 2025 at 11:34 AM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote: > > On Wed, 2025-08-27 at 10:32 -0700, Andrii Nakryiko wrote: > > 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(-) > > The CI found an issue with bpf-gcc in the meantime, I will fix this in > v3. > > > > 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? > > Will do. > > > > > > /* 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? > > It should be fine according to [1]: > > Compatible attribute specifications on distinct declarations of the > same function are merged. > > I will add this to the commit message in v3. Sure, for BPF selftests it will work. My question was broader, for anyone using bpf_obj_new in the wild, they won't have __must_check annotation from vmlinux.h (and I doubt they will manually add it like we do here for BPF selftests), so if that's important, I guess we need to think how to wire that up so that it happens automatically through vmlinux.h. "It's not that important to bother" is a fine answer as well :) > > [1] > https://gcc.gnu.org/onlinedocs/gcc-12.4.0/gcc/Function-Attributes.html > > [...]
