在 2025/3/28 01:19, Song Liu 写道:
Hi Tao,
Compiler optimizations can cause issues for tracing kernel functions. Please
refer to Yonghong and Alan's presentation [1] for various cases.
Thanks,
Song
[1] https://lpc.events/event/18/contributions/1945/
Hi Song,
Thank you for the materials you provided. I'll take a look at them.
On Thu, Mar 27, 2025 at 9:03 AM Tao Chen <chen.dylane@xxxxxxxxx> wrote:
Hi,
I recently encountered a problem when using fentry to trace kernel
functions optimized by compiler, the specific situation is as follows:
https://github.com/bpftrace/bpftrace/issues/3940
Simply put, some functions have been optimized by the compiler. The
original function names are found through BTF, but the optimized
functions are the ones that exist in kallsyms_lookup_name. Therefore,
the two do not match.
func_proto = btf_type_by_id(desc_btf, func->type);
if (!func_proto || !btf_type_is_func_proto(func_proto)) {
verbose(env, "kernel function btf_id %u does not have a
valid func_proto\n",
func_id);
return -EINVAL;
}
func_name = btf_name_by_offset(desc_btf, func->name_off);
addr = kallsyms_lookup_name(func_name);
if (!addr) {
verbose(env, "cannot find address for kernel function
%s\n",
func_name);
return -EINVAL;
}
I have made a simple statistics and there are approximately more than
2,000 functions in Ubuntu 24.04.
dylane@2404:~$ cat /proc/kallsyms | grep isra | wc -l
2324
So can we add a judgment from libbpf. If it is an optimized function,
pass the suffix of the optimized function from the user space to the
kernel, and then perform a function name concatenation, like:
func_name = btf_name_by_offset(desc_btf, func->name_off);
if (optimize) {
func_name = func_name + ".isra.0"
}
addr = kallsyms_lookup_name(func_name);
--
Best Regards
Tao Chen
--
Best Regards
Tao Chen
