On Tue, Aug 22, 2023 at 4:06 PM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Tue, Aug 22, 2023 at 3:54 PM Kumar Kartikeya Dwivedi > <memxor@xxxxxxxxx> wrote: > > > > > > I suppose we could switch to the ' if (!(LHS <op> RHS)) bpf_throw(); ' > > sequence in C, force volatile load for LHS and __builtin_constant_p > > for RHS to get the same behavior. Emitting these redundant checks is > > definitely a bit weird just to emit BTF. > > I guess we can try > #define bpf_assert(LHS, OP, RHS) if (!(LHS OP RHS)) bpf_throw(); > with barrier_var(LHS) and __builtin_constant_p(RHS) and > keep things completely in C, > but there is no guarantee that the compiler will not convert == to !=, > swap lhs and rhs, etc. > Maybe we can have both asm and C style macros, then recommend C to start > and switch to asm if things are dodgy. > Feels like dangerous ambiguity. This seems similar to the issue I had with __attribute__((cleanup(some_kfunc)))) not emitting BTF info for that some_kfunc? See bpf_for_each(), seems like just adding `(void)bpf_iter_##type##_destroy` makes Clang emit BTF info. It would be nice to have this fixed for cleanup() attribute and asm, of course. But this is a simple work around.
