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bpftool: Un-const bpf_func_info to fix it for llvm 17 and newer

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LLVM 17 started treating const structs as constants:

* 0b2d5b967d

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@mail.gmail.com/T/

Fixes: b662000aff ("bpftool: Adding support for BTF program names")
Signed-off-by: Ivan Babrou <ivan@cloudflare.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240520225149.5517-1-ivan@cloudflare.com
This commit is contained in:
Ivan Babrou 2024-05-20 15:51:49 -07:00 • committed by Andrii Nakryiko
parent 6f130e4d4a
commit f4aba3471c
1 changed files with 1 additions and 1 deletions
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2
tools/bpf/bpftool/common.c
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@ -410,7 +410,7 @@ void get_prog_full_name(const struct bpf_prog_info *prog_info, int prog_fd,
{
const char *prog_name = prog_info->name;
const struct btf_type *func_type;
const struct bpf_func_info finfo = {};
struct bpf_func_info finfo = {};
struct bpf_prog_info info = {};
__u32 info_len = sizeof(info);
struct btf *prog_btf = NULL;