Re: [PATCH v2] tracing/uprobe: Add missing PID filter for uretprobe

Oleg Nesterov
2024-08-26T21:26:15Z

This is offtopic, sorry for the spam, but...

On 08/26, Jiri Olsa wrote:
>
> On Mon, Aug 26, 2024 at 01:57:52PM +0200, Oleg Nesterov wrote:
> >
> > Does bpftrace use bpf_uprobe_multi_link_attach/etc ? I guess not...
> > Then which userspace tool uses this code? ;)
>
> yes, it will trigger if you attach to multiple uprobes, like with your
> test example with:
>
> # bpftrace -p xxx -e 'uprobe:./ex:func* { printf("%d\n", pid); }'

Hmm. I reserved the testing machine with fedora 40 to play with bpftrace.

dummy.c:

#include <unistd.h>

void func1(void) {}
void func2(void) {}

int main(void) { for (;;) pause(); }

If I do

# ./dummy &
# bpftrace -p $! -e 'uprobe:./dummy:func* { printf("%d\n", pid); }'

and run

# bpftrace -e 'kprobe:__uprobe_register { printf("%s\n", kstack); }'

on another console I get

Attaching 1 probe...

__uprobe_register+1
probe_event_enable+399
perf_trace_event_init+440
perf_uprobe_init+152
perf_uprobe_event_init+74
perf_try_init_event+71
perf_event_alloc+1681
__do_sys_perf_event_open+447
do_syscall_64+130
entry_SYSCALL_64_after_hwframe+118

__uprobe_register+1
probe_event_enable+399
perf_trace_event_init+440
perf_uprobe_init+152
perf_uprobe_event_init+74
perf_try_init_event+71
perf_event_alloc+1681
__do_sys_perf_event_open+447
do_syscall_64+130
entry_SYSCALL_64_after_hwframe+118

so it seems that bpftrace doesn't use bpf_uprobe_multi_link_attach()
(called by sys_bpf(BPF_LINK_CREATE) ?) in this case.

But again, this is offtopic, please forget.

Oleg.