On Mon, 2024-12-16 at 10:05 -0800, Alexei Starovoitov wrote: [...] > > Thanks for the review! Good point, I'll try to write them in C. > > > > It might not be possible to do them both entirely: clang also doesn't > > know that bpf_tail_call() can return, so it assumes the callee() will > > return a constant r0. It sometimes optimizes branches / loads out > > because of this. > > I wonder whether we should tell llvm that it's similar to longjmp() > with __attribute__((noreturn)) or some other attribute. GCC documents it as follows [1]: > The noreturn keyword tells the compiler to assume that fatal > cannot reaturn. It can then optimize without regard to what would > happen if fatal ever did return. This makes slightly better code. > More importantly, it helps avoid spurious warnings of > uninitialized variables. But the bpf_tail_call could return if MAX_TAIL_CALL_CNT limit is exceeded, or programs map index is out of bounds. [1] https://gcc.gnu.org/onlinedocs/gcc-14.2.0/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute
