On Thu, Mar 31, 2022 at 6:34 PM Song Chen <chensong_2000@xxxxxx> wrote:
>
> When i was writing my eBPF program, i copied some pieces of code from
> syscall_tp, syscall_tp_kern only records how many files are opened, but
> mine needs to print file name.I reused struct syscalls_enter_open_args,
> which is defined as:
>
> struct syscalls_enter_open_args {
> unsigned long long unused;
> long syscall_nr;
> long filename_ptr;
> long flags;
> long mode;
> };
>
> I tried to use filename_ptr, but it's not the pointer of filename, flags
> turns out to be the pointer I'm looking for, there might be something
> missed in the struct.
>
> I read the ftrace log, found the missed one is dfd, which is supposed to be
> placed in between syscall_nr and filename_ptr.
>
> Actually syscall_tp has nothing to do with dfd, it can run anyway without
> it, but it's better to have it to make it a better eBPF sample, especially
> to new eBPF programmers, then i fixed it.
>
> Signed-off-by: Song Chen <chensong_2000@xxxxxx>
> ---
> samples/bpf/syscall_tp_kern.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/samples/bpf/syscall_tp_kern.c b/samples/bpf/syscall_tp_kern.c
> index 50231c2eff9c..e4ac818aee57 100644
> --- a/samples/bpf/syscall_tp_kern.c
> +++ b/samples/bpf/syscall_tp_kern.c
> @@ -7,6 +7,7 @@
> struct syscalls_enter_open_args {
> unsigned long long unused;
> long syscall_nr;
> + long dfd_ptr;
> long filename_ptr;
> long flags;
> long mode;
Here's what I see on latest bpf-next:
# cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_open/format
name: sys_enter_open
ID: 613
format:
field:unsigned short common_type; offset:0;
size:2; signed:0;
field:unsigned char common_flags; offset:2;
size:1; signed:0;
field:unsigned char common_preempt_count; offset:3;
size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;
field:int __syscall_nr; offset:8; size:4; signed:1;
field:const char * filename; offset:16; size:8; signed:0;
field:int flags; offset:24; size:8; signed:0;
field:umode_t mode; offset:32; size:8; signed:0;
This layout doesn't correspond either to before or after state of
syscalls_enter_open_args. Not sure what's going on, but it doesn't
seem that struct syscalls_enter_open_args is correct anyways.
> --
> 2.25.1
>
