On Wed, 13 Sept 2023 at 01:32, Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote: > > This series implements the _first_ part of the runtime and verifier > support needed to enable BPF exceptions. Exceptions thrown from programs > are processed as an immediate exit from the program, which unwinds all > the active stack frames until the main stack frame, and returns to the > BPF program's caller. The ability to perform this unwinding safely > allows the program to test conditions that are always true at runtime > but which the verifier has no visibility into. > > [...] Hi everyone, just to make sure this is not missed, I had to revert back to the ASM approach as I found the C approach to be too fragile during testing. David asked whether we could move this facility into libbpf as well, but I think with the current state it is probably better to let things sit in bpf_experimental.h for a while. The problem with BTF info generation for such ksyms still remains, I tried and kept the (void)bpf_throw suggestion from Andrii but I'm not sure it helps in every case, atleast with clang 17 I can reduce the program to a simple case where it doesn't produce the BTF info needed for successful loading. For now, another no-overhead solution can be having a bpf_throw call that never executes in a static function that is never used. The libbpf loading process will never append this to the main program's instruction sequence (since unreferenced), it will just be there in the object.
