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 <[email protected]>
---
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
On Mon, May 20, 2024 at 3:52 PM Ivan Babrou <[email protected]> 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.
Right, looks like we don't currently have UBSan instrumentation for "I
modified an object declared const." Instead, it just leads to fun
bugs like "why was my write elided" or in this case "why did my
constant folding change between compiler versions?" Such are the joys
of UB.
Acked-by: Nick Desaulniers <[email protected]>
>
> 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 <[email protected]>
> ---
> 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
>
--
Thanks,
~Nick Desaulniers
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@mail.gmail.com/T/
>
> Fixes: b662000aff84 ("bpftool: Adding support for BTF program names")
> Signed-off-by: Ivan Babrou <[email protected]>
Acked-by: Yonghong Song <[email protected]>
Hello:
This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <[email protected]>:
On Mon, 20 May 2024 15:51:49 -0700 you 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.
>
> [...]
Here is the summary with links:
- bpftool: un-const bpf_func_info to fix it for llvm 17 and newer
https://git.kernel.org/bpf/bpf-next/c/f4aba3471cfb
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html