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Subject[PATCH 18/20 v2] tracing/perf: Allow perf to use function based events
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Have perf use function based events.

# echo 'SyS_openat(int dfd, string buf, x32 flags, x32 mode)' > /sys/kernel/tracing/function_events
# perf record -e functions:SyS_openat grep task_forks /proc/kallsyms
# perf script
grep 913 [002] 5713.413239: functions:SyS_openat: entry_SYSCALL_64_fastpath->sys_openat(dfd=-100, buf=/proc/kallsyms, flags=100, mode=0)

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
Documentation/trace/function-based-events.rst | 3 +-
kernel/trace/trace_event_ftrace.c | 134 ++++++++++++++++++++------
2 files changed, 104 insertions(+), 33 deletions(-)

diff --git a/Documentation/trace/function-based-events.rst b/Documentation/trace/function-based-events.rst
index 3b341992b93d..6effde96d3d6 100644
--- a/Documentation/trace/function-based-events.rst
+++ b/Documentation/trace/function-based-events.rst
@@ -48,7 +48,8 @@ enable filter format hist id trigger

Even though the above function based event does not record much more
than the function tracer does, it does become a full fledge event.
-This can be used by the histogram infrastructure, and triggers.
+This can be used by the histogram infrastructure, triggers, and perf
+where one can attach eBPF programs to.

# cat events/functions/do_IRQ/format
name: do_IRQ
diff --git a/kernel/trace/trace_event_ftrace.c b/kernel/trace/trace_event_ftrace.c
index 732ba570466b..303a56c3339a 100644
--- a/kernel/trace/trace_event_ftrace.c
+++ b/kernel/trace/trace_event_ftrace.c
@@ -749,46 +749,33 @@ static int get_string(unsigned long addr, unsigned int idx,
return len;
}

-static void func_event_trace(struct trace_event_file *trace_file,
- struct func_event *func_event,
- unsigned long ip, unsigned long parent_ip,
- struct pt_regs *pt_regs)
+static int get_event_size(struct func_event *func_event, struct pt_regs *pt_regs,
+ long *args, int *nr_args)
{
- struct func_event_hdr *entry;
- struct trace_event_call *call = &func_event->call;
- struct ring_buffer_event *event;
- struct ring_buffer *buffer;
- struct func_arg *arg;
- long args[func_event->arg_cnt];
- long long val = 1;
- unsigned long irq_flags;
- int str_offset;
- int str_idx = 0;
- int nr_args = 0;
int size;
- int pc;
-
- if (trace_trigger_soft_disabled(trace_file))
- return;
-
- local_save_flags(irq_flags);
- pc = preempt_count();

- size = func_event->arg_offset + sizeof(*entry);
+ size = func_event->arg_offset + sizeof(struct func_event_hdr);

if (func_event->arg_cnt)
- nr_args = arch_get_func_args(pt_regs, 0, func_event->arg_cnt, args);
+ *nr_args = arch_get_func_args(pt_regs, 0, func_event->arg_cnt, args);
+ else
+ *nr_args = 0;

if (func_event->has_strings)
- size += calculate_strings(func_event, nr_args, args);
+ size += calculate_strings(func_event, *nr_args, args);

- event = trace_event_buffer_lock_reserve(&buffer, trace_file,
- call->event.type,
- size, irq_flags, pc);
- if (!event)
- return;
+ return size;
+}
+
+static void
+record_entry(struct func_event_hdr *entry, struct func_event *func_event,
+ unsigned long ip, unsigned long parent_ip, int nr_args, long *args)
+{
+ struct func_arg *arg;
+ long long val;
+ int str_offset;
+ int str_idx = 0;

- entry = ring_buffer_event_data(event);
entry->ip = ip;
entry->parent_ip = parent_ip;

@@ -811,11 +798,80 @@ static void func_event_trace(struct trace_event_file *trace_file,
} else
memcpy(&entry->data[arg->offset], &val, arg->size);
}
+}
+
+static void func_event_trace(struct trace_event_file *trace_file,
+ struct func_event *func_event,
+ unsigned long ip, unsigned long parent_ip,
+ struct pt_regs *pt_regs)
+{
+ struct func_event_hdr *entry;
+ struct trace_event_call *call = &func_event->call;
+ struct ring_buffer_event *event;
+ struct ring_buffer *buffer;
+ long args[func_event->arg_cnt];
+ unsigned long irq_flags;
+ int nr_args;
+ int size;
+ int pc;
+
+ if (trace_trigger_soft_disabled(trace_file))
+ return;
+
+ local_save_flags(irq_flags);
+ pc = preempt_count();
+
+ size = get_event_size(func_event, pt_regs, args, &nr_args);
+
+ event = trace_event_buffer_lock_reserve(&buffer, trace_file,
+ call->event.type,
+ size, irq_flags, pc);
+ if (!event)
+ return;

+ entry = ring_buffer_event_data(event);
+ record_entry(entry, func_event, ip, parent_ip, nr_args, args);
event_trigger_unlock_commit_regs(trace_file, buffer, event,
entry, irq_flags, pc, pt_regs);
}

+#ifdef CONFIG_PERF_EVENTS
+/* Kprobe profile handler */
+static void func_event_perf(struct func_event *func_event,
+ unsigned long ip, unsigned long parent_ip,
+ struct pt_regs *pt_regs)
+{
+ struct trace_event_call *call = &func_event->call;
+ struct func_event_hdr *entry;
+ struct hlist_head *head;
+ long args[func_event->arg_cnt];
+ int nr_args = 0;
+ int rctx;
+ int size;
+
+ if (bpf_prog_array_valid(call) && !trace_call_bpf(call, pt_regs))
+ return;
+
+ head = this_cpu_ptr(call->perf_events);
+ if (hlist_empty(head))
+ return;
+
+ size = get_event_size(func_event, pt_regs, args, &nr_args);
+
+ entry = perf_trace_buf_alloc(size, NULL, &rctx);
+ if (!entry)
+ return;
+
+ record_entry(entry, func_event, ip, parent_ip, nr_args, args);
+ perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, pt_regs,
+ head, NULL);
+}
+#else
+static inline void func_event_perf(struct func_event *func_event,
+ unsigned long ip, unsigned long parent_ip,
+ struct pt_regs *pt_regs) { }
+#endif
+
static void
func_event_call(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op, struct pt_regs *pt_regs)
@@ -830,7 +886,10 @@ func_event_call(unsigned long ip, unsigned long parent_ip,
rcu_irq_enter_irqson();
rcu_read_lock_sched_notrace();
list_for_each_entry_rcu(ff, &func_event->files, list) {
- func_event_trace(ff->file, func_event, ip, parent_ip, pt_regs);
+ if (ff->file)
+ func_event_trace(ff->file, func_event, ip, parent_ip, pt_regs);
+ else
+ func_event_perf(func_event, ip, parent_ip, pt_regs);
}
rcu_read_unlock_sched_notrace();
rcu_irq_exit_irqson();
@@ -1047,6 +1106,17 @@ static int func_event_register(struct trace_event_call *event,
return enable_func_event(func_event, file);
case TRACE_REG_UNREGISTER:
return disable_func_event(func_event, file);
+#ifdef CONFIG_PERF_EVENTS
+ case TRACE_REG_PERF_REGISTER:
+ return enable_func_event(func_event, NULL);
+ case TRACE_REG_PERF_UNREGISTER:
+ return disable_func_event(func_event, NULL);
+ case TRACE_REG_PERF_OPEN:
+ case TRACE_REG_PERF_CLOSE:
+ case TRACE_REG_PERF_ADD:
+ case TRACE_REG_PERF_DEL:
+ return 0;
+#endif
default:
break;
}
--
2.15.1

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