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Message-ID: <20240520225149.5517-1-ivan@cloudflare.com>
Date: Mon, 20 May 2024 15:51:49 -0700
From: Ivan Babrou <ivan@...udflare.com>
To: bpf@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
kernel-team@...udflare.com,
Ivan Babrou <ivan@...udflare.com>,
Quentin Monnet <quentin@...valent.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Tom Rix <trix@...hat.com>,
Raman Shukhau <ramasha@...com>
Subject: [PATCH] bpftool: un-const bpf_func_info to fix it for llvm 17 and newer
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@mail.gmail.com/T/
Fixes: b662000aff84 ("bpftool: Adding support for BTF program names")
Signed-off-by: Ivan Babrou <ivan@...udflare.com>
---
tools/bpf/bpftool/common.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
index cc6e6aae2447..6d8bbc3ec603 100644
--- a/tools/bpf/bpftool/common.c
+++ b/tools/bpf/bpftool/common.c
@@ -338,7 +338,7 @@ 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;
--
2.44.0
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