On Thu, Sep 10, 2009 at 07:53:30PM -0400, Masami Hiramatsu wrote:
+#ifdef CONFIG_EVENT_PROFILE
+
+/* Kprobe profile handler */
+static __kprobes int kprobe_profile_func(struct kprobe *kp,
+ struct pt_regs *regs)
+{
+ struct trace_probe *tp = container_of(kp, struct trace_probe, rp.kp);
+ struct ftrace_event_call *call =&tp->call;
+ struct kprobe_trace_entry *entry;
+ int size, i, pc;
+ unsigned long irq_flags;
+
+ local_save_flags(irq_flags);
+ pc = preempt_count();
+
+ size = SIZEOF_KPROBE_TRACE_ENTRY(tp->nr_args);
Note that the end-result must be u64 aligned for perf ring buffer.
And this is a bit tricky.
What is inserted in the perf ring buffer is:
raw_trace + (u32)raw_trace_size
So we must ensure that sizeof(raw_trace) + sizeof(u32)
is well u64 aligned.
We don't insert the trace_size ourself though, this is done
from kernel/perf_counter.c
But we need to handle the size of the size (sorry) in the final
alignment.
To sum-up: sizeof(raw_trace) doesn't need (shouldn't) to be u64
aligned but sizeof(raw_trace) + sizeof(u32) must be.
Given this aligned size, we then substract it by sizeof(u32)
to have the needed size of the raw entry.
This result gives you the size of char raw_data[], which
is also the same size passed in perf_tpcounter_event().
See?
That's why we have this in trace/ftrace.h:
__data_size = "the real entry data size"
__entry_size = ALIGN(__data_size + sizeof(*entry) + sizeof(u32), sizeof(u64));
__entry_size -= sizeof(u32);
do {
char raw_data[__entry_size];
...
perf_tpcounter_event(event_call->id, __addr, __count, entry,
__entry_size);
...
} while (0);