Re: sys_enter tracepoint ctx structure

[Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>]

On Sun, Apr 23, 2023 at 2:04 AM Yauheni Kaliuta <ykaliuta@xxxxxxxxxx> wrote:
>
> Hi, Alexei!
>
> >>>>> On Fri, 21 Apr 2023 09:02:34 -0700, Alexei Starovoitov  wrote:
>  > On Fri, Apr 21, 2023 at 4:17 AM Yauheni Kaliuta <ykaliuta@xxxxxxxxxx> wrote:
>  >> >>>>> On Thu, 20 Apr 2023 16:12:49 -0700, Alexei Starovoitov  wrote:
>  >> > On Thu, Apr 20, 2023 at 2:40 PM Yauheni Kaliuta <ykaliuta@xxxxxxxxxx> wrote:
>  >> >> >>>>> On Thu, 20 Apr 2023 13:54:26 -0700, Alexei Starovoitov  wrote:
>  >> >> > On Thu, Apr 20, 2023 at 1:37 PM Yauheni Kaliuta <ykaliuta@xxxxxxxxxx> wrote:
>  >> >> >> >>>>> On Thu, 20 Apr 2023 08:59:09 -0700, Alexei Starovoitov  wrote:
>
> [...]
>
>  >> > Let's fix the kernel side too. Something like this should do it:
>  >>
>  >> > diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
>  >> > index 942ddbdace4a..7aa1f4299486 100644
>  >> > --- a/kernel/trace/trace_syscalls.c
>  >> > +++ b/kernel/trace/trace_syscalls.c
>  >> > @@ -555,7 +555,7 @@ static int perf_call_bpf_enter(struct
>  >> > trace_event_call *call, struct pt_regs *re
>  >> >                                struct syscall_trace_enter *rec)
>  >> >  {
>  >> >         struct syscall_tp_t {
>  >> > -               unsigned long long regs;
>  >> > +               struct trace_entry ent;
>  >> >                 unsigned long syscall_nr;
>  >> >                 unsigned long args[SYSCALL_DEFINE_MAXARGS];
>  >> >         } param;
>  >> > @@ -657,7 +657,7 @@ static int perf_call_bpf_exit(struct
>  >> > trace_event_call *call, struct pt_regs *reg
>  >> >                               struct syscall_trace_exit *rec)
>  >> >  {
>  >> >         struct syscall_tp_t {
>  >> > -               unsigned long long regs;
>  >> > +               struct trace_entry ent;
>  >>
>  >>
>  >> > pls add build_bug_on that sizeof(ent) >= sizeof(void*).
>  >>
>  >> Ok. Should the line *(struct pt_regs **)&param = regs; be commented somehow?
>
>  > commented out?
>
> No, no :)
>
>  > No. It's mandatory.
>  > And the reason for build_bug_on existence... to make sure that there
>  > is enough space there.
>
> Yes, it's clear for sure.
>
> It can be not obvious why basically 'ent' is inited with
> 'regs'. Before it was called 'regs' at least.

Got it :) Yeah. A comment describing the intent would be nice.