> 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.
Besides, please keep in mind that GCC doens't have an integrated
assembler, and therefore relying on clang's understanding on the
instructions in inline assembly is something to avoid.
> There are also options like the one below to work around it.
> if ((volatile int){0}) bpf_throw();
> asm volatile ("call bpf_throw");
I can confirm the above results in a BTF entry for bpf_throw with
bpf-unknown-none-gcc -gbtf.
