On Wed, 9 Aug 2023 at 17:11, Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote:
>
> [...]
>
> Known issues
> ------------
>
> * Just asm volatile ("call bpf_throw" :::) does not emit DATASEC .ksyms
> for bpf_throw, there needs to be explicit call in C for clang to emit
> the DATASEC info in BTF, leading to errors during compilation.
>
Hi Yonghong, I'd like to ask you about this issue to figure out
whether this is something worth fixing in clang or not.
It pops up in programs which only use bpf_assert macros (which emit
the call to bpf_throw using inline assembly) and not bpf_throw kfunc
directly.
I believe in case we emit a call bpf_throw instruction, the BPF
backend code will not see any DWARF debug info for the respective
symbol, so it will also not be able to convert it and emit anything to
.BTF section in case no direct call without asm volatile is present.
Therefore my guess is that this isn't something that can be fixed in clang/LLVM.
There are also options like the one below to work around it.
if ((volatile int){0}) bpf_throw();
asm volatile ("call bpf_throw");
