Re: [PATCH -tip v8 7/7] tracing: add kprobe-based event tracer

Steven Rostedt
2009-05-30T04:11:26Z

On Thu, 28 May 2009, Masami Hiramatsu wrote:

> +#undef SHOW_FIELD
> +#define SHOW_FIELD(type, item, name) \
> + do { \
> + ret = trace_seq_printf(s, "\tfield: " #type " %s;\t" \
> + "offset:%u;tsize:%u;\n", name, \
> + (unsigned)offsetof(typeof(field), item),\
> + (unsigned)sizeof(type)); \
> + if (!ret) \
> + return 0; \
> + } while (0)
> +
> +static int __probe_event_show_format(struct ftrace_event_call *event_call,
> + struct trace_seq *s, const char *fmt,
> + const char *arg)
> +{
> + struct kprobe_trace_entry field __attribute__((unused));

You use kprobe_trace_entry for both kprobe and kretprobe.

> + int ret, i;
> + char buf[MAX_ARGSTR_LEN + 1];
> + struct trace_probe *tp = container_of(event_call,
> + struct trace_probe, call);
> +
> + /* Show fields */
> + for (i = 0; i < tp->nr_args; i++) {
> + sprintf(buf, "arg%d", i);
> + SHOW_FIELD(unsigned long, args[i], buf);
> + }
> + trace_seq_puts(s, "\n");
> +
> + /* Show aliases */
> + for (i = 0; i < tp->nr_args; i++) {
> + if (trace_arg_string(buf, MAX_ARGSTR_LEN, &tp->args[i]))
> + return 0;
> + if (!trace_seq_printf(s, "\talias: %s;\toriginal: arg%d;\n",
> + buf, i))
> + return 0;
> + }
> + /* Show format */
> + if (!trace_seq_printf(s, "\nprint fmt: \"%s", fmt))
> + return 0;
> +
> + for (i = 0; i < tp->nr_args; i++)
> + if (!trace_seq_puts(s, " 0x%lx"))
> + return 0;
> +
> + if (!trace_seq_printf(s, "\", %s", arg))
> + return 0;
> +
> + for (i = 0; i < tp->nr_args; i++)
> + if (!trace_seq_printf(s, ", arg%d", i))
> + return 0;
> +
> + return trace_seq_puts(s, "\n");
> +}
> +
> +static int kprobe_event_show_format(struct ftrace_event_call *call,
> + struct trace_seq *s)
> +{
> + struct kprobe_trace_entry field __attribute__((unused));
> + int ret;
> +
> + SHOW_FIELD(unsigned long, ip, "ip");
> + SHOW_FIELD(int, nargs, "nargs");
> +
> + return __probe_event_show_format(call, s, "%lx:", "ip");
> +}
> +
> +static int kretprobe_event_show_format(struct ftrace_event_call *call,
> + struct trace_seq *s)
> +{
> + struct kretprobe_trace_entry field __attribute__((unused));
> + int ret;
> +
> + SHOW_FIELD(unsigned long, func, "func");
> + SHOW_FIELD(unsigned long, ret_ip, "ret_ip");
> + SHOW_FIELD(int, nargs, "nargs");
> +
> + return __probe_event_show_format(call, s, "%lx <- %lx:",
> + "func, ret_ip");
> +}

Thus we end up with:

format:
field:unsigned short common_type; offset:0; size:2;
field:unsigned char common_flags; offset:2; size:1;
field:unsigned char common_preempt_count; offset:3;
size:1;
field:int common_pid; offset:4; size:4;
field:int common_tgid; offset:8; size:4;

field: unsigned long func; offset:16;tsize:8;
field: unsigned long ret_ip; offset:24;tsize:8;
field: int nargs; offset:32;tsize:4;
field: unsigned long arg0; offset:32;tsize:8;
field: unsigned long arg1; offset:40;tsize:8;
field: unsigned long arg2; offset:48;tsize:8;
field: unsigned long arg3; offset:56;tsize:8;

Notice that nargs and arg0 are both at offest 32.

-- Steve