noinstr code

/**
 * atomic_read() - atomic load with relaxed ordering
 * @v: pointer to atomic_t
 *
 * Atomically loads the value of @v with relaxed ordering.
 *
 * Unsafe to use in noinstr code; use raw_atomic_read() there.
 *
 * Return: The value loaded from @v.
 */
static __always_inline int
atomic_read(const atomic_t *v)
{
	instrument_atomic_read(v, sizeof(*v));
	return raw_atomic_read(v);
}

相当于有的代码是不可以插桩的，如果那些不能插桩的代码想要使用 atomic_read 的时候， 那么就需要使用 raw_atomic_read

一共存在那些 trace 类型

/*
 * Event flags:
 *  CAP_ANY	  - Any user can enable for perf
 *  NO_SET_FILTER - Set when filter has error and is to be ignored
 *  IGNORE_ENABLE - For trace internal events, do not enable with debugfs file
 *  TRACEPOINT    - Event is a tracepoint
 *  DYNAMIC       - Event is a dynamic event (created at run time)
 *  KPROBE        - Event is a kprobe
 *  UPROBE        - Event is a uprobe
 *  EPROBE        - Event is an event probe
 *  FPROBE        - Event is an function probe
 *  CUSTOM        - Event is a custom event (to be attached to an exsiting tracepoint)
 *                   This is set when the custom event has not been attached
 *                   to a tracepoint yet, then it is cleared when it is.
 *  TEST_STR      - The event has a "%s" that points to a string outside the event
 */
enum {
	TRACE_EVENT_FL_CAP_ANY		= (1 << TRACE_EVENT_FL_CAP_ANY_BIT),
	TRACE_EVENT_FL_NO_SET_FILTER	= (1 << TRACE_EVENT_FL_NO_SET_FILTER_BIT),
	TRACE_EVENT_FL_IGNORE_ENABLE	= (1 << TRACE_EVENT_FL_IGNORE_ENABLE_BIT),
	TRACE_EVENT_FL_TRACEPOINT	= (1 << TRACE_EVENT_FL_TRACEPOINT_BIT),
	TRACE_EVENT_FL_DYNAMIC		= (1 << TRACE_EVENT_FL_DYNAMIC_BIT),
	TRACE_EVENT_FL_KPROBE		= (1 << TRACE_EVENT_FL_KPROBE_BIT),
	TRACE_EVENT_FL_UPROBE		= (1 << TRACE_EVENT_FL_UPROBE_BIT),
	TRACE_EVENT_FL_EPROBE		= (1 << TRACE_EVENT_FL_EPROBE_BIT),
	TRACE_EVENT_FL_FPROBE		= (1 << TRACE_EVENT_FL_FPROBE_BIT),
	TRACE_EVENT_FL_CUSTOM		= (1 << TRACE_EVENT_FL_CUSTOM_BIT),
	TRACE_EVENT_FL_TEST_STR		= (1 << TRACE_EVENT_FL_TEST_STR_BIT),
};

那么如何理解 DYNAMIC ?

此外，如何理解 tracefs 中的 dynamic_events ?

bcc 也可以同时观测多个函数

通过 funccount 可以发现

sudo funccount "tty_lock*"

Tracing 3 functions for "b'tty_lock*'"... Hit Ctrl-C to end.
^C
FUNC                                    COUNT
tty_lock_slave                              5
tty_lock                                    8
Detaching...

类似的，bpftrace 也是可以的:

sudo bpftrace -e 'kprobe:*_martins3 { printf("%s\n", func) }'

不过，这个正则展开到底是内核中做的，还是用户态做的可以确认一下，我认为这个是用户态做的。

而通过 tracefs ，显然是通过内核做的。

本站所有文章转发 CSDN 将按侵权追究法律责任，其它情况随意。