Re: [PATCH] bpftool: un-const bpf_func_info to fix it for llvm 17 and newer

[Yonghong Song]

On 5/20/24 4:51 PM, Ivan Babrou wrote:
> LLVM 17 started treating const structs as constants:
>
> * https://github.com/llvm/llvm-project/commit/0b2d5b967d98
>
> Combined with pointer laundering via ptr_to_u64, which takes a const ptr,
> but in reality treats the underlying memory as mutable, this makes clang
> always pass zero to btf__type_by_id, which breaks full name resolution.
>
> Disassembly before (LLVM 16) and after (LLVM 17):
>
>      -    8b 75 cc                 mov    -0x34(%rbp),%esi
>      -    e8 47 8d 02 00           call   3f5b0 <btf__type_by_id>
>      +    31 f6                    xor    %esi,%esi
>      +    e8 a9 8c 02 00           call   3f510 <btf__type_by_id>
>
> It's a bigger project to fix this properly (and a question whether LLVM
> itself should detect this), but for right now let's just fix bpftool.
>
> For more information, see this thread in bpf mailing list:
>
> * https://lore.kernel.org/bpf/CABWYdi0ymezpYsQsPv7qzpx2fWuTkoD1-wG1eT-9x-TSREFrQg@xxxxxxxxxxxxxx/T/
>
> Fixes: b662000aff84 ("bpftool: Adding support for BTF program names")
> Signed-off-by: Ivan Babrou <ivan@xxxxxxxxxxxxxx>

Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>