观察 Linux 内核中的变量(内存地址)变化，并在变化时打印堆栈跟踪? [英] Watch a variable (memory address) change in Linux kernel, and print stack trace when it changes?
问题描述
我想以某种方式在 Linux 内核(确切地说是内核模块/驱动程序)中观察"一个变量(或内存地址)；并找出是什么改变了它——基本上，当变量改变时打印出堆栈跟踪.
I would like to somehow "watch" a variable (or a memory address, rather) in the Linux kernel (a kernel module/driver, to be exact); and find out what changed it - basically, print out a stack trace when the variable changed.
例如，在这个答案，我想在每次 runcount 变量更改时打印出堆栈跟踪；希望堆栈跟踪将包含提及 testjiffy_timer_function，这确实是更改该变量的函数.
For instance, in the kernel module testjiffy-hr.c listed at end of this answer, I would like to print out a stack trace each time the runcount variable changes; hopefully the stack trace then would contain a mention of testjiffy_timer_function, which is indeed the function that changes that variable.
现在，我知道我可以使用 kgdb 连接到在虚拟机中运行的调试 Linux 内核，甚至可以像这样设置断点(希望也是观察点) - 但问题是我实际上想调试一个 ALSA 驱动程序，特别是回放 dma_area 缓冲区(我在那里得到了一些意外数据)——它对时间高度敏感；并且运行调试内核本身会弄乱时间(更不用说在虚拟机中运行它了).
Now, I know I can use kgdb to connect to a debug Linux kernel running in say a virtual machine, and even set breakpoints (so hopefully, also watchpoints) like that - but the problem is that I actually want to debug an ALSA driver, in particular the playback dma_area buffer (where I'm getting some unexpected data) - which is highly sensitive to timing; and running the debug kernel in itself would mess up the timings (let alone running it in a virtual machine).
这里一个更大的问题是播放dma_area指针仅在播放操作期间存在(或者换句话说，在_start和_stop之间)code> 处理程序) - 所以我必须在每个 _start 回调中记录 dma_area 地址，然后在播放操作期间以某种方式安排"它以观看".
An even bigger problem here is that the playback dma_area pointer exists only during a playback operation (or in other words, between the _start and _stop handlers) - so I'd have to record the dma_area address at each _start callback, and then somehow "schedule" it for "watching" during the playback operation.
所以我希望有一种方法可以直接在驱动程序代码中做这样的事情 - 例如，在这个记录 dma_area 的 _start 回调中添加一些代码指针，并将其用作启动监视"更改的命令的参数；从相应的回调函数打印堆栈跟踪.(我知道这也会影响时间，但我希望它足够轻"，不会过多地影响实时"驱动程序操作).
So I was hoping there was a way to do something like this directly in the driver code - as in, add some code in this _start callback which records the dma_area pointer, and use it as an argument to a command which initiates the "watch" for a change; with the stack trace printed from a corresponding callback function. (I'm aware that this too would influence the timing, but I was hoping it would be "light" enough not to influence the "live" driver operation too much).
所以我的问题是:在 Linux 内核中是否存在这种用于调试的技术?
So my question is: does such a technique for debugging in the Linux kernel exist?
如果不是:是否可以设置硬件(或软件)中断，对特定内存地址的变化做出反应?那么我可以设置这样一个中断处理程序，它可以打印出堆栈跟踪吗?(虽然，我认为当 IRQ 处理程序运行时整个上下文会发生变化，因此获取堆栈跟踪可能会出错)?
If not: is it possible to set up a hardware (or software) interrupt, that reacts on a change of a specific memory address? Then could I set up such an interrupt handler, that could print out a stack trace? (although, I think the whole context changes when IRQ handlers run, so maybe getting a stack trace there would be wrong)?
如果没有:是否还有其他技术可以让我打印进程的堆栈跟踪，该进程更改了存储在内核中给定内存位置的值(希望在实时的非调试内核中)?
If not: are there any other techniques left, that would allow me to print a stack trace of the process that changed the value stored in a given memory location in the kernel ( hopefully in a live, non-debug kernel)?
推荐答案
非常感谢 @CosminRatiu 和尤金;多亏了这些，我发现:
Many thanks for the replies by @CosminRatiu and Eugene; thanks to those, I found:
... 用它我可以开发我在这里发布的示例，testhrarr.c 内核模块/驱动程序和 Makefile(如下).它证明了硬件观察点跟踪可以通过两种方式实现:一种是使用perf程序，它可以不变地探测驱动程序；或者通过向驱动程序添加一些硬件断点代码(在示例中，由 HWDEBUG_STACK 定义变量封装).
... with which I could develop the example I'm posting here, the testhrarr.c kernel module/driver and the Makefile (below). It demonstrates that the hardware watchpoint tracing can be achieved in two ways: either using the perf program, which can probe the driver unchanged; or by adding some hardware breakpoint code to the driver (in the example, enveloped by the HWDEBUG_STACK define variable).
本质上，调试标准原子变量类型如 ints(如 runcount 变量)的内容很简单，只要它们在内核模块中定义为全局变量，因此它们最终会显示作为全局内核符号.因此，下面的代码添加了 testhrarr_ 作为变量的前缀(以避免命名冲突).然而，由于需要取消引用，调试数组的内容可能有点棘手 - 这就是这篇文章所演示的，调试 testhrarr_arr 数组的第一个字节.完成于:
Essentially, debugging contents of standard atomic variable types like ints (like the runcount variable) are straightforward, as long as they are defined as a global variable in the kernel module, so they end up showing as a kernel symbol globally. Because of that, the code below adds the testhrarr_ as prefix to the variables (so as to avoid naming conflicts). However, debugging contents of arrays may be a bit trickier, due to the need for dereferencing - so that is what this post demonstrates, debug of the first byte of the testhrarr_arr array. It was done on:
$ echo `cat /etc/lsb-release`
DISTRIB_ID=Ubuntu DISTRIB_RELEASE=11.04 DISTRIB_CODENAME=natty DISTRIB_DESCRIPTION="Ubuntu 11.04"
$ uname -a
Linux mypc 2.6.38-16-generic #67-Ubuntu SMP Thu Sep 6 18:00:43 UTC 2012 i686 i686 i386 GNU/Linux
$ cat /proc/cpuinfo | grep "model name"
model name : Intel(R) Atom(TM) CPU N450 @ 1.66GHz
model name : Intel(R) Atom(TM) CPU N450 @ 1.66GHz
testhrarr 模块基本上是在模块初始化时为一个小数组分配内存，设置一个定时器函数，并暴露一个 /proc/testhrarr_proc 文件(使用较新的<代码>proc_create 接口).然后，尝试从 /proc/testhrarr_proc 文件中读取(例如，使用 cat)将触发计时器功能，该功能将修改 testhrarr_arr数组值，并将消息转储到 /var/log/syslog.我们预计testhrarr_arr[0]在操作过程中会变化3次；一次在 testhrarr_startup 中，两次在 testhrarr_timer_function 中(由于包装).
The testhrarr module basically allocates memory for a small array upon module initialization, sets up a timer function, and exposes a /proc/testhrarr_proc file (using the newer proc_create interface). Then, attempting to read from the /proc/testhrarr_proc file (say, using cat) will trigger the timer function, which will modify the testhrarr_arr array values, and dump messages to /var/log/syslog. We expect that testhrarr_arr[0] will change three times during the operation; once in testhrarr_startup, and twice in testhrarr_timer_function (due to wrapping).
使用make构建模块后，您可以使用:
After building the module with make, you can load it with:
sudo insmod ./testhrarr.ko
此时，/var/log/syslog 将包含:
kernel: [40277.199913] Init testhrarr: 0 ; HZ: 250 ; 1/HZ (ms): 4 ; hrres: 0.000000001
kernel: [40277.199930] Addresses: _runcount 0xf84be22c ; _arr 0xf84be2a0 ; _arr[0] 0xed182a80 (0xed182a80) ; _timer_function 0xf84bc1c3 ; my_hrtimer 0xf84be260; my_hrt.f 0xf84be27c
kernel: [40277.220329] HW Breakpoint for testhrarr_arr write installed (0xf84be2a0)
请注意，仅将 testhrarr_arr 作为硬件观察点的符号传递会扫描该变量的地址(0xf84be2a0)，而不是数组的第一个元素的地址(0xed182a80)！正因为如此，硬件断点不会被触发——所以行为就好像硬件断点代码根本不存在一样(这可以通过取消定义HWDEBUG_STACK)！
Note that just passing testhrarr_arr as symbol for hardware watchpoint scans the address of that variable (0xf84be2a0), not the address of the first element of the array (0xed182a80)! Because of this, the hardware breakpoint is not going to trigger - so the behavior will be as if the hardware breakpoint code is not present at all (which can be achieved by undefining HWDEBUG_STACK)!
因此，即使没有通过内核模块代码设置硬件断点，我们仍然可以使用 perf 来观察内存地址的变化 - 在 perf 中，我们指定两者我们要观察的地址(这里是testhrarr_arr的第一个元素的地址，0xed182a80)，以及应该运行的进程:这里我们运行bash，所以我们可以执行一个 cat/proc/testhrarr_proc 这将触发内核模块计时器，然后是一个 sleep 0.5 这将使计时器完成.-a 参数也是需要的，否则可能会漏掉一些事件:
So, even without a hardware breakpoint set through kernel module code, we can still use perf to observe a change of a memory address - in perf, we specify both the address we want to watch (here the address of the first element of testhrarr_arr, 0xed182a80), and the process which should be ran: here we run bash, so we can execute a cat /proc/testhrarr_proc which will trigger the kernel module timer, followed by a sleep 0.5 which will allow the timer to complete. The -a parameter is also needed, otherwise some events may be missed:
$ sudo perf record -a --call-graph --event=mem:0xed182a80:w bash -c 'cat /proc/testhrarr_proc ; sleep 0.5'
testhrarr proc: startup
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.485 MB perf.data (~21172 samples) ]
此时，/var/log/syslog 也将包含如下内容:
At this point, /var/log/syslog would also contain something like:
[40822.114964] testhrarr_timer_function: testhrarr_runcount 0
[40822.114980] testhrarr jiffies 10130528 ; ret: 1 ; ktnsec: 40822114975062
[40822.118956] testhrarr_timer_function: testhrarr_runcount 1
[40822.118977] testhrarr jiffies 10130529 ; ret: 1 ; ktnsec: 40822118973195
[40822.122940] testhrarr_timer_function: testhrarr_runcount 2
[40822.122956] testhrarr jiffies 10130530 ; ret: 1 ; ktnsec: 40822122951143
[40822.126962] testhrarr_timer_function: testhrarr_runcount 3
[40822.126978] testhrarr jiffies 10130531 ; ret: 1 ; ktnsec: 40822126973583
[40822.130941] testhrarr_timer_function: testhrarr_runcount 4
[40822.130961] testhrarr jiffies 10130532 ; ret: 1 ; ktnsec: 40822130955167
[40822.134940] testhrarr_timer_function: testhrarr_runcount 5
[40822.134962] testhrarr jiffies 10130533 ; ret: 1 ; ktnsec: 40822134958888
[40822.138936] testhrarr_timer_function: testhrarr_runcount 6
[40822.138958] testhrarr jiffies 10130534 ; ret: 1 ; ktnsec: 40822138955693
[40822.142940] testhrarr_timer_function: testhrarr_runcount 7
[40822.142962] testhrarr jiffies 10130535 ; ret: 1 ; ktnsec: 40822142959345
[40822.146936] testhrarr_timer_function: testhrarr_runcount 8
[40822.146957] testhrarr jiffies 10130536 ; ret: 1 ; ktnsec: 40822146954479
[40822.150949] testhrarr_timer_function: testhrarr_runcount 9
[40822.150970] testhrarr jiffies 10130537 ; ret: 1 ; ktnsec: 40822150963438
[40822.154974] testhrarr_timer_function: testhrarr_runcount 10
[40822.154988] testhrarr [ 5, 7, 9, 11, 13, ]
要读取 perf(一个名为 perf.data 的文件)的捕获，我们可以使用:
To read the capture of perf (a file called perf.data) we can use:
$ sudo perf report --call-graph flat --stdio
No kallsyms or vmlinux with build-id 5031df4d8668bcc45a7bdb4023909c6f8e2d3d34 was found
[testhrarr] with build id 5031df4d8668bcc45a7bdb4023909c6f8e2d3d34 not found, continuing without symbols
Failed to open /bin/cat, continuing without symbols
Failed to open /usr/lib/libpixman-1.so.0.20.2, continuing without symbols
Failed to open /usr/lib/xorg/modules/drivers/intel_drv.so, continuing without symbols
Failed to open /usr/bin/Xorg, continuing without symbols
# Events: 5 unknown
#
# Overhead Command Shared Object Symbol
# ........ ....... ............. ....................................
#
87.50% Xorg [testhrarr] [k] testhrarr_timer_function
87.50%
testhrarr_timer_function
__run_hrtimer
hrtimer_interrupt
smp_apic_timer_interrupt
apic_timer_interrupt
0x30185d
0x2ed701
0x2ed8cc
0x2edba0
0x9d0386
0x8126fc8
0x81217a1
0x811bdd3
0x8070aa7
0x806281c
__libc_start_main
0x8062411
6.25% cat [testhrarr] [k] testhrarr_timer_function
6.25%
testhrarr_timer_function
testhrarr_proc_show
seq_read
proc_reg_read
vfs_read
sys_read
syscall_call
0xaa2416
0x8049f4d
__libc_start_main
0x8049081
3.12% swapper [testhrarr] [k] testhrarr_timer_function
3.12%
testhrarr_timer_function
__run_hrtimer
hrtimer_interrupt
smp_apic_timer_interrupt
apic_timer_interrupt
cpuidle_idle_call
cpu_idle
start_secondary
3.12% cat [testhrarr] [k] 0x356
3.12%
0xf84bc356
0xf84bc3a7
seq_read
proc_reg_read
vfs_read
sys_read
syscall_call
0xaa2416
0x8049f4d
__libc_start_main
0x8049081
#
# (For a higher level overview, try: perf report --sort comm,dso)
#
因此，由于我们正在构建内核模块并调试(Makefile 中的-g)，因此对于 perf 来查找此模块的符号，即使实时内核不是调试内核.所以它在大多数情况下正确地将 testhrarr_timer_function 解释为 setter，尽管它没有报告 testhrarr_startup(但它确实报告了调用它的 testhrarr_proc_show).还有对 0xf84bc3a7 和 0xf84bc356 的引用，它无法解析；但是，请注意该模块是在 0xf84bc000 处加载的:
So, since we're building the kernel module with debugging on (-g in the Makefile), it is not a problem for perf to find this module's symbols, even if the live kernel is not a debug kernel. So it correctly interprets testhrarr_timer_function as the setter most of the time, although it doesn't report testhrarr_startup (but it does report testhrarr_proc_show which calls it). There are also references to 0xf84bc3a7 and 0xf84bc356 which it couldn't resolve; however, note that the module is loaded at 0xf84bc000:
$ sudo cat /proc/modules | grep testhr
testhrarr 13433 0 - Live 0xf84bc000
... 并且该条目也以 ...[k] 0x356 开头；如果我们查看内核模块的objdump:
... and that entry also starts with ...[k] 0x356; and if we look in the objdump of the kernel module:
$ objdump -S testhrarr.ko | less
...
00000323 :
static void testhrarr_startup(void)
{
...
testhrarr_arr[0] = 0; //just the first element
34b: a1 80 00 00 00 mov 0x80,%eax
350: c7 00 00 00 00 00 movl $0x0,(%eax)
hrtimer_start(&my_hrtimer, ktime_period_ns, HRTIMER_MODE_REL);
356: c7 04 24 01 00 00 00 movl $0x1,(%esp) **********
35d: 8b 15 1c 00 00 00 mov 0x1c,%edx
...
00000375 :
static int testhrarr_proc_show(struct seq_file *m, void *v) {
...
seq_printf(m, "testhrarr proc: startup
");
38f: c7 44 24 04 79 00 00 movl $0x79,0x4(%esp)
396: 00
397: 8b 45 fc mov -0x4(%ebp),%eax
39a: 89 04 24 mov %eax,(%esp)
39d: e8 fc ff ff ff call 39e
testhrarr_startup();
3a2: e8 7c ff ff ff call 323
3a7: eb 1c jmp 3c5 **********
} else {
seq_printf(m, "testhrarr proc: (is running, %d)
", testhrarr_runcount);
3a9: a1 0c 00 00 00 mov 0xc,%eax
...
... 所以 0xf84bc356 显然是指 hrtimer_start;而 0xf84bc3a7 -> 3a7 指的是它调用的 testhrarr_proc_show 函数；谢天谢地，这是有道理的.(请注意，我使用过不同版本的驱动程序，_start 可以显示，timer_function 由纯粹的地址表示；不确定这是什么原因).
... so 0xf84bc356 apparently refers to hrtimer_start; and 0xf84bc3a7 -> 3a7 refers to its calling testhrarr_proc_show function; which thankfully makes sense. (Note that I've experienced with different versions of the driver, that the _start could show, and the timer_function to be expressed by sheer addresses; not sure what this is due).
perf 的一个问题是，它为我提供了这些函数发生的统计开销"(不确定这是指什么 - 可能在进入和退出函数之间花费的时间?) - 但我真正想要的是一个连续的堆栈跟踪日志.不确定是否可以为此设置 perf - 但它肯定可以通过硬件断点的内核模块代码来完成.
One problem with perf, though, is that it gives me a statistical "Overhead" of these functions occurring (not sure what that refers to - probably time spent between entry and exit of a function?) - but what I want, really, is a log of stack traces which is sequential. Not sure if perf can be set up for that - but it definitely be done with kernel module code for hardware breakpoints.
HWDEBUG_STACK 中的代码实现了硬件断点的设置和处理.如前所述，符号 ksym_name(如果未指定)的默认设置是 testhrarr_arr，它根本不会触发硬件断点.ksym_name 参数可以在insmod 时在命令行指定；在这里我们可以注意到:
The code which is in the HWDEBUG_STACK implements the HW breakpoint setup and handling. As noted, the default set up for the symbol ksym_name (if unspecified), is testhrarr_arr, which doesn't trigger the hardware breakpoint at all. The ksym_name parameter can be specified on the command line during insmod; here we can note that:
$ sudo rmmod testhrarr # remove module if still loaded
$ sudo insmod ./testhrarr.ko ksym=testhrarr_arr[0]
... 结果是 HW Breakpoint for testhrarr_arr[0] write installed (0x (null)) in /var/log/syslog;- 这意味着我们不能使用带括号表示法的符号来访问数组；谢天谢地，这里的空指针只是意味着硬件断点不会再次触发；它不会使操作系统完全崩溃 :)
... results with a HW Breakpoint for testhrarr_arr[0] write installed (0x (null)) in /var/log/syslog; - which means we cannot use symbols with bracket notation for array access; thankfully a null pointer here simply means that HW breakpoint will again not fire; it doesn't crash the OS completely :)
然而，有一个全局变量用于引用 testhrarr_arr 数组的第一个元素，称为 testhrarr_arr_first - 注意这个全局变量是如何在代码，需要解引用，才能得到正确的地址.所以我们这样做:
There is, however, a global variable made to refer to the first element of the testhrarr_arr array, called testhrarr_arr_first - note how this global variable is specially handled in the code, and needs to be dereferenced, so that the correct address is obtained. So we do:
$ sudo rmmod testhrarr # remove module if still loaded
$ sudo insmod ./testhrarr.ko ksym=testhrarr_arr_first
... 系统日志通知:
... and the syslog informs:
kernel: [43910.509726] Init testhrarr: 0 ; HZ: 250 ; 1/HZ (ms): 4 ; hrres: 0.000000001
kernel: [43910.509765] Addresses: _runcount 0xf84be22c ; _arr 0xf84be2a0 ; _arr[0] 0xedf6c5c0 (0xedf6c5c0) ; _timer_function 0xf84bc1c3 ; my_hrtimer 0xf84be260; my_hrt.f 0xf84be27c
kernel: [43910.538535] HW Breakpoint for testhrarr_arr_first write installed (0xedf6c5c0)
...我们可以看到硬件断点设置在0xedf6c5c0，也就是testhrarr_arr[0]的地址.现在，如果我们通过 /proc 文件触发驱动程序:
... and we can see that the HW breakpoint is set at 0xedf6c5c0, which is the address of testhrarr_arr[0]. Now if we trigger the driver via the /proc file:
$ cat /proc/testhrarr_proc
testhrarr proc: startup
...我们在syslog中获得:
kernel: [44069.735695] testhrarr_arr_first value is changed
[44069.735711] Pid: 29320, comm: cat Not tainted 2.6.38-16-generic #67-Ubuntu
[44069.735719] Call Trace:
[44069.735737] [] ? sample_hbp_handler+0x2d/0x3b [testhrarr]
[44069.735755] [] ? __perf_event_overflow+0x90/0x240
[44069.735768] [] ? proc_alloc_inode+0x23/0x90
[44069.735778] [] ? proc_alloc_inode+0x23/0x90
[44069.735790] [] ? perf_swevent_event+0x136/0x140
[44069.735801] [] ? perf_bp_event+0x70/0x80
[44069.735812] [] ? prep_new_page+0x110/0x1a0
[44069.735824] [] ? get_page_from_freelist+0x12e/0x320
[44069.735836] [] ? seq_open+0x3d/0xa0
[44069.735848] [] ? hw_breakpoint_handler.clone.0+0x102/0x130
[44069.735861] [] ? hw_breakpoint_exceptions_notify+0x22/0x30
[44069.735872] [] ? notifier_call_chain+0x45/0x60
[44069.735883] [] ? atomic_notifier_call_chain+0x22/0x30
[44069.735894] [] ? notify_die+0x2d/0x30
[44069.735904] [] ? do_debug+0x88/0x180
[44069.735915] [] ? debug_stack_correct+0x30/0x38
[44069.735928] [] ? testhrarr_startup+0x33/0x52 [testhrarr]
[44069.735940] [] ? testhrarr_proc_show+0x32/0x57 [testhrarr]
[44069.735952] [] ? seq_read+0x145/0x390
[44069.735963] [] ? seq_read+0x0/0x390
[44069.735973] [] ? proc_reg_read+0x64/0xa0
[44069.735985] [] ? vfs_read+0x9f/0x160
[44069.735995] [] ? proc_reg_read+0x0/0xa0
[44069.736003] [] ? sys_read+0x42/0x70
[44069.736013] [] ? syscall_call+0x7/0xb
[44069.736019] Dump stack from sample_hbp_handler
[44069.740132] testhrarr_timer_function: testhrarr_runcount 0
[44069.740146] testhrarr jiffies 10942435 ; ret: 1 ; ktnsec: 44069740142485
[44069.740159] testhrarr_arr_first value is changed
[44069.740169] Pid: 4302, comm: gnome-terminal Not tainted 2.6.38-16-generic #67-Ubuntu
[44069.740176] Call Trace:
[44069.740195] [] ? sample_hbp_handler+0x2d/0x3b [testhrarr]
[44069.740213] [] ? __perf_event_overflow+0x90/0x240
[44069.740227] [] ? perf_swevent_event+0x136/0x140
[44069.740239] [] ? perf_bp_event+0x70/0x80
[44069.740253] [] ? sched_clock_local+0xd3/0x1c0
[44069.740267] [] ? format_decode+0x323/0x380
[44069.740280] [] ? hw_breakpoint_handler.clone.0+0x102/0x130
[44069.740292] [] ? hw_breakpoint_exceptions_notify+0x22/0x30
[44069.740302] [] ? notifier_call_chain+0x45/0x60
[44069.740313] [] ? atomic_notifier_call_chain+0x22/0x30
[44069.740324] [] ? notify_die+0x2d/0x30
[44069.740335] [] ? do_debug+0x88/0x180
[44069.740345] [] ? debug_stack_correct+0x30/0x38
[44069.740364] [] ? init_intel_cacheinfo+0x103/0x394
[44069.740379] [] ? testhrarr_timer_function+0xed/0x160 [testhrarr]
[44069.740391] [] ? __run_hrtimer+0x6f/0x190
[44069.740404] [] ? testhrarr_timer_function+0x0/0x160 [testhrarr]
[44069.740416] [] ? hrtimer_interrupt+0x108/0x240
[44069.740430] [] ? smp_apic_timer_interrupt+0x56/0x8a
[44069.740441] [] ? apic_timer_interrupt+0x31/0x38
[44069.740453] [] ? _raw_spin_unlock_irqrestore+0x15/0x20
[44069.740465] [] ? try_to_del_timer_sync+0x67/0xb0
[44069.740476] [] ? del_timer_sync+0x29/0x50
[44069.740486] [] ? flush_delayed_work+0x13/0x40
[44069.740500] [] ? tty_flush_to_ldisc+0x12/0x20
[44069.740510] [] ? n_tty_poll+0x4f/0x190
[44069.740523] [] ? tty_poll+0x6d/0x90
[44069.740531] [] ? n_tty_poll+0x0/0x190
[44069.740542] [] ? do_poll.clone.3+0xd0/0x210
[44069.740553] [] ? do_sys_poll+0x134/0x1e0
[44069.740563] [] ? __pollwait+0x0/0xd0
[44069.740572] [] ? pollwake+0x0/0x60
...
[44069.740742] [] ? pollwake+0x0/0x60
[44069.740757] [] ? rw_verify_area+0x6c/0x130
[44069.740770] [] ? ktime_get_ts+0xf8/0x120
[44069.740781] [] ? poll_select_set_timeout+0x64/0x70
[44069.740793] [] ? sys_poll+0x5a/0xd0
[44069.740804] [] ? syscall_call+0x7/0xb
[44069.740815] [] ? init_intel_cacheinfo+0x23/0x394
[44069.740822] Dump stack from sample_hbp_handler
[44069.744130] testhrarr_timer_function: testhrarr_runcount 1
[44069.744143] testhrarr jiffies 10942436 ; ret: 1 ; ktnsec: 44069744140055
[44069.748132] testhrarr_timer_function: testhrarr_runcount 2
[44069.748145] testhrarr jiffies 10942437 ; ret: 1 ; ktnsec: 44069748141271
[44069.752131] testhrarr_timer_function: testhrarr_runcount 3
[44069.752145] testhrarr jiffies 10942438 ; ret: 1 ; ktnsec: 44069752141164
[44069.756131] testhrarr_timer_function: testhrarr_runcount 4
[44069.756141] testhrarr jiffies 10942439 ; ret: 1 ; ktnsec: 44069756138318
[44069.760130] testhrarr_timer_function: testhrarr_runcount 5
[44069.760141] testhrarr jiffies 10942440 ; ret: 1 ; ktnsec: 44069760138469
[44069.760154] testhrarr_arr_first value is changed
[44069.760164] Pid: 4302, comm: gnome-terminal Not tainted 2.6.38-16-generic #67-Ubuntu
[44069.760170] Call Trace:
[44069.760187] [] ? sample_hbp_handler+0x2d/0x3b [testhrarr]
[44069.760202] [] ? __perf_event_overflow+0x90/0x240
[44069.760213] [] ? perf_swevent_event+0x136/0x140
[44069.760224] [] ? perf_bp_event+0x70/0x80
[44069.760235] [] ? sched_clock_local+0xd3/0x1c0
[44069.760247] [] ? format_decode+0x323/0x380
[44069.760258] [] ? hw_breakpoint_handler.clone.0+0x102/0x130
[44069.760269] [] ? hw_breakpoint_exceptions_notify+0x22/0x30
[44069.760279] [] ? notifier_call_chain+0x45/0x60
[44069.760289] [] ? atomic_notifier_call_chain+0x22/0x30
[44069.760299] [] ? notify_die+0x2d/0x30
[44069.760308] [] ? do_debug+0x88/0x180
[44069.760318] [] ? debug_stack_correct+0x30/0x38
[44069.760334] [] ? init_intel_cacheinfo+0x103/0x394
[44069.760345] [] ? testhrarr_timer_function+0xed/0x160 [testhrarr]
[44069.760356] [] ? __run_hrtimer+0x6f/0x190
[44069.760366] [] ? send_to_group.clone.1+0xf8/0x150
[44069.760376] [] ? testhrarr_timer_function+0x0/0x160 [testhrarr]
[44069.760387] [] ? hrtimer_interrupt+0x108/0x240
[44069.760396] [] ? fsnotify+0x1a5/0x290
[44069.760407] [] ? smp_apic_timer_interrupt+0x56/0x8a
[44069.760416] [] ? apic_timer_interrupt+0x31/0x38
[44069.760428] [] ? mem_cgroup_resize_limit+0x108/0x1c0
[44069.760437] [] ? fput+0x0/0x30
[44069.760446] [] ? sys_write+0x67/0x70
[44069.760455] [] ? syscall_call+0x7/0xb
[44069.760464] [] ? init_intel_cacheinfo+0x23/0x394
[44069.760470] Dump stack from sample_hbp_handler
[44069.764134] testhrarr_timer_function: testhrarr_runcount 6
[44069.764147] testhrarr jiffies 10942441 ; ret: 1 ; ktnsec: 44069764144141
[44069.768133] testhrarr_timer_function: testhrarr_runcount 7
[44069.768146] testhrarr jiffies 10942442 ; ret: 1 ; ktnsec: 44069768142976
[44069.772134] testhrarr_timer_function: testhrarr_runcount 8
[44069.772148] testhrarr jiffies 10942443 ; ret: 1 ; ktnsec: 44069772144121
[44069.776132] testhrarr_timer_function: testhrarr_runcount 9
[44069.776145] testhrarr jiffies 10942444 ; ret: 1 ; ktnsec: 44069776141971
[44069.780133] testhrarr_timer_function: testhrarr_runcount 10
[44069.780141] testhrarr [ 5, 7, 9, 11, 13, ]...我们准确地获得了三次堆栈跟踪 - 一次是在 testhrarr_startup 期间，两次是在 testhrarr_timer_function:一次是 runcount==0> 和一次用于 runcount==5，正如预期的那样.
... we get a stack trace exactly three times - once during testhrarr_startup, and twice in testhrarr_timer_function: once for runcount==0 and once for runcount==5, as expected.
好吧，希望这对某人有所帮助，
干杯！
Well, hope this helps someone,
Cheers!
Makefile
CONFIG_MODULE_FORCE_UNLOAD=y
# debug build:
# "CFLAGS was changed ... Fix it to use EXTRA_CFLAGS."
override EXTRA_CFLAGS+=-g -O0
obj-m += testhrarr.o
#testhrarr-objs := testhrarr.o
all:
@echo EXTRA_CFLAGS = $(EXTRA_CFLAGS)
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
testhrarr.c
/*
* [http://www.tldp.org/LDP/lkmpg/2.6/html/lkmpg.html#AEN189 The Linux Kernel Module Programming Guide]
* https://stackoverflow.com/questions/16920238/reliability-of-linux-kernel-add-timer-at-resolution-of-one-jiffy/17055867#17055867
* https://stackoverflow.com/questions/8516021/proc-create-example-for-kernel-module/18924359#18924359
* http://lxr.free-electrons.com/source/samples/hw_breakpoint/data_breakpoint.c
*/
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_INFO */
#include <linux/init.h> /* Needed for the macros */
#include <linux/jiffies.h>
#include <linux/time.h>
#include <linux/proc_fs.h> /* /proc entry */
#include <linux/seq_file.h> /* /proc entry */
#define ARRSIZE 5
#define MAXRUNS 2*ARRSIZE
#include <linux/hrtimer.h>
#define HWDEBUG_STACK 1
#if (HWDEBUG_STACK == 1)
#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
struct perf_event * __percpu *sample_hbp;
static char ksym_name[KSYM_NAME_LEN] = "testhrarr_arr";
module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
" write operations on the kernel symbol");
#endif
static volatile int testhrarr_runcount = 0;
static volatile int testhrarr_isRunning = 0;
static unsigned long period_ms;
static unsigned long period_ns;
static ktime_t ktime_period_ns;
static struct hrtimer my_hrtimer;
static int* testhrarr_arr;
static int* testhrarr_arr_first;
static enum hrtimer_restart testhrarr_timer_function(struct hrtimer *timer)
{
unsigned long tjnow;
ktime_t kt_now;
int ret_overrun;
printk(KERN_INFO
" %s: testhrarr_runcount %d
",
__func__, testhrarr_runcount);
if (testhrarr_runcount < MAXRUNS) {
tjnow = jiffies;
kt_now = hrtimer_cb_get_time(&my_hrtimer);
ret_overrun = hrtimer_forward(&my_hrtimer, kt_now, ktime_period_ns);
printk(KERN_INFO
" testhrarr jiffies %lu ; ret: %d ; ktnsec: %lld
",
tjnow, ret_overrun, ktime_to_ns(kt_now));
testhrarr_arr[(testhrarr_runcount % ARRSIZE)] += testhrarr_runcount;
testhrarr_runcount++;
return HRTIMER_RESTART;
}
else {
int i;
testhrarr_isRunning = 0;
// do not use KERN_DEBUG etc, if printk buffering until newline is desired!
printk("testhrarr_arr [ ");
for(i=0; i<ARRSIZE; i++) {
printk("%d, ", testhrarr_arr[i]);
}
printk("]
");
return HRTIMER_NORESTART;
}
}
static void testhrarr_startup(void)
{
if (testhrarr_isRunning == 0) {
testhrarr_isRunning = 1;
testhrarr_runcount = 0;
testhrarr_arr[0] = 0; //just the first element
hrtimer_start(&my_hrtimer, ktime_period_ns, HRTIMER_MODE_REL);
}
}
static int testhrarr_proc_show(struct seq_file *m, void *v) {
if (testhrarr_isRunning == 0) {
seq_printf(m, "testhrarr proc: startup
");
testhrarr_startup();
} else {
seq_printf(m, "testhrarr proc: (is running, %d)
", testhrarr_runcount);
}
return 0;
}
static int testhrarr_proc_open(struct inode *inode, struct file *file) {
return single_open(file, testhrarr_proc_show, NULL);
}
static const struct file_operations testhrarr_proc_fops = {
.owner = THIS_MODULE,
.open = testhrarr_proc_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
#if (HWDEBUG_STACK == 1)
static void sample_hbp_handler(struct perf_event *bp,
struct perf_sample_data *data,
struct pt_regs *regs)
{
printk(KERN_INFO "%s value is changed
", ksym_name);
dump_stack();
printk(KERN_INFO "Dump stack from sample_hbp_handler
");
}
#endif
static int __init testhrarr_init(void)
{
struct timespec tp_hr_res;
#if (HWDEBUG_STACK == 1)
struct perf_event_attr attr;
#endif
period_ms = 1000/HZ;
hrtimer_get_res(CLOCK_MONOTONIC, &tp_hr_res);
printk(KERN_INFO
"Init testhrarr: %d ; HZ: %d ; 1/HZ (ms): %ld ; hrres: %lld.%.9ld
",
testhrarr_runcount, HZ, period_ms, (long long)tp_hr_res.tv_sec, tp_hr_res.tv_nsec );
testhrarr_arr = (int*)kcalloc(ARRSIZE, sizeof(int), GFP_ATOMIC);
testhrarr_arr_first = &testhrarr_arr[0];
hrtimer_init(&my_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
my_hrtimer.function = &testhrarr_timer_function;
period_ns = period_ms*( (unsigned long)1E6L );
ktime_period_ns = ktime_set(0,period_ns);
printk(KERN_INFO
" Addresses: _runcount 0x%p ; _arr 0x%p ; _arr[0] 0x%p (0x%p) ; _timer_function 0x%p ; my_hrtimer 0x%p; my_hrt.f 0x%p
",
&testhrarr_runcount, &testhrarr_arr, &(testhrarr_arr[0]), testhrarr_arr_first, &testhrarr_timer_function, &my_hrtimer, &my_hrtimer.function);
proc_create("testhrarr_proc", 0, NULL, &testhrarr_proc_fops);
#if (HWDEBUG_STACK == 1)
hw_breakpoint_init(&attr);
if (strcmp(ksym_name, "testhrarr_arr_first") == 0) {
// just for testhrarr_arr_first - interpret the found symbol address
// as int*, and dereference it to get the "real" address it points to
attr.bp_addr = *((int*)kallsyms_lookup_name(ksym_name));
} else {
// the usual - address is kallsyms_lookup_name result
attr.bp_addr = kallsyms_lookup_name(ksym_name);
}
attr.bp_len = HW_BREAKPOINT_LEN_1;
attr.bp_type = HW_BREAKPOINT_W ; //| HW_BREAKPOINT_R;
sample_hbp = register_wide_hw_breakpoint(&attr, (perf_overflow_handler_t)sample_hbp_handler);
if (IS_ERR((void __force *)sample_hbp)) {
int ret = PTR_ERR((void __force *)sample_hbp);
printk(KERN_INFO "Breakpoint registration failed
");
return ret;
}
// explicit cast needed to show 64-bit bp_addr as 32-bit address
// https://stackoverflow.com/questions/11796909/how-to-resolve-cast-to-pointer-from-integer-of-different-size-warning-in-c-co/11797103#11797103
printk(KERN_INFO "HW Breakpoint for %s write installed (0x%p)
", ksym_name, (void*)(uintptr_t)attr.bp_addr);
#endif
return 0;
}
static void __exit testhrarr_exit(void)
{
int ret_cancel = 0;
kfree(testhrarr_arr);
while( hrtimer_callback_running(&my_hrtimer) ) {
ret_cancel++;
}
if (ret_cancel != 0) {
printk(KERN_INFO " testhrarr Waited for hrtimer callback to finish (%d)
", ret_cancel);
}
if (hrtimer_active(&my_hrtimer) != 0) {
ret_cancel = hrtimer_cancel(&my_hrtimer);
printk(KERN_INFO " testhrarr active hrtimer cancelled: %d (%d)
", ret_cancel, testhrarr_runcount);
}
if (hrtimer_is_queued(&my_hrtimer) != 0) {
ret_cancel = hrtimer_cancel(&my_hrtimer);
printk(KERN_INFO " testhrarr queued hrtimer cancelled: %d (%d)
", ret_cancel, testhrarr_runcount);
}
remove_proc_entry("testhrarr_proc", NULL);
#if (HWDEBUG_STACK == 1)
unregister_wide_hw_breakpoint(sample_hbp);
printk(KERN_INFO "HW Breakpoint for %s write uninstalled
", ksym_name);
#endif
printk(KERN_INFO "Exit testhrarr
");
}
module_init(testhrarr_init);
module_exit(testhrarr_exit);
MODULE_LICENSE("GPL");
这篇关于观察 Linux 内核中的变量(内存地址)变化，并在变化时打印堆栈跟踪?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
