调试 – 观察Linux内核中的变量(内存地址)更改,并在更改时打印堆栈跟踪？

我想以某种方式“监视” Linux内核中的变量(或内存地址)(确切地说是内核模块/驱动程序);并找出改变它的原因 – 基本上,当变量改变时打印出堆栈跟踪.

例如,在this answer年末列出的内核模块testjiffy-hr.c中,我想在每次runcount变量更改时打印出堆栈跟踪;希望堆栈跟踪然后会提到testjiffy_timer_function,这确实是改变该变量的函数.

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,甚至可以设置断点(所以希望也是观察点) – 但问题是我实际上想要调试ALSA驱动程序,特别是播放dma_area缓冲区(我得到了一些意想不到的数据) – 这对时间非常敏感;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.

这里更大的问题是回放dma_area指针仅在回放操作期间(或者换句话说,在_start和_stop处理程序之间)存在 – 所以我必须在每个_start回调中记录dma_area地址,然后以某种方式“在播放操作期间安排“用于”观看“.

所以我希望有一种方法可以直接在驱动程序代码中执行此类操作 – 例如,在此_start回调中添加一些代码来记录dma_area指针,并将其用作启动“watch”的命令的参数改变;从相应的回调函数打印堆栈跟踪. (我知道这也会影响时间,但我希望它能够“轻松”,不会过多地影响“实时”驱动程序操作).

所以我的问题是：在Linux内核中进行调试的这种技术是否存在？

如果不是：是否可以设置硬件(或软件)中断,该中断会对特定内存地址的更改做出反应？然后,我可以设置这样的中断处理程序,可以打印出堆栈跟踪吗？ (虽然,我认为整个上下文在IRQ处理程序运行时会发生变化,因此可能会出现堆栈跟踪错误)？

如果没有：是否还有其他技术,这将允许我打印进程的堆栈跟踪,该跟踪更改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)？

解决方法

非常感谢 @CosminRatiu和 Eugene的回复;多亏了那些,我发现：

> debugging – Linux kernel hardware break points – Stack Overflow
> Hardware Breakpoint (or watchpoint) – The Linux Kernel Archives

…我可以用它来开发我在这里发布的示例,testhrarr.c内核模块/驱动程序和Makefile(下面).它表明硬件观察点跟踪可以通过两种方式实现：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定义变量包含).

本质上,调试像int这样的标准原子变量类型(如runcount变量)的内容很简单,只要它们被定义为内核模块中的全局变量,因此它们最终全局显示为内核符号.因此,下面的代码将testhrarr_添加为变量的前缀(以避免命名冲突).但是,由于需要解除引用,调试数组的内容可能有点棘手 – 这就是本文演示的内容,调试testhrarr_arr数组的第一个字节.它完成于：

$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模块基本上在模块初始化时为小数组分配内存,设置定时器函数,并公开/ proc / testhrarr_proc文件(使用较新的proc_create接口).然后,尝试从/ proc / testhrarr_proc文件(例如,使用cat)读取将触发计时器功能,该功能将修改testhrarr_arr数组值,并将消息转储到/ var / log / syslog.我们期望testhrarr_arr [0]在操作期间会改变三次;一次在testhrarr_startup中,两次在testhrarr_timer_function中(由于换行).

使用perf

使用make构建模块后,您可以使用以下命令加载它：

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)

注意,只是将testhrarr_arr作为硬件观察点的符号传递,扫描该变量的地址(0xf84be2a0),而不是数组的第一个元素的地址(0xed182a80)！因此,硬件断点不会触发 – 因此行为就好像硬件断点代码根本不存在(可以通过取消定义HWDEBUG_STACK来实现)！

因此,即使没有通过内核模块代码设置的硬件断点,我们仍然可以使用perf来观察内存地址的变化 – 在perf中,我们指定我们要监视的地址(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cat / proc / testhrarr_proc,它将触发内核模块定时器,然后是sleep 0.5,这将允许定时器完成. -a参数也是必需的,否则可能会遗漏一些事件：

$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还包含以下内容：

^{[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：

$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,由于我们正在使用调试on(Makefile中的-g)构建内核模块,所以即使实时内核不是调试内核,perf也不能找到该模块的符号.所以它在大多数时候正确地将testhrarr_timer_function解释为setter,虽然它没有报告testhrarr_startup(但它报告了testhrarr_proc_show调用它).还有对0xf84bc3a7和0xf84bc356的引用无法解析;但请注意,模块加载为0xf84bc000：

$sudo cat /proc/modules | grep testhr
testhrarr 13433 0 - Live 0xf84bc000

……并且该条目也以…开头[k] 0x356;如果我们查看内核模块的objdump：

$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\n");
 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)\n",testhrarr_runcount);
 3a9:   a1 0c 00 00 00          mov    0xc,%eax
...}

…所以0xf84bc356显然是指hrtimer_start;和0xf84bc3a7 – > 3a7指其调用testhrarr_proc_show函数;值得庆幸的是. (请注意,我已经体验过不同版本的驱动程序,_start可以显示,而timer_function由纯粹的地址表示;不确定是什么原因).

然而,perf的一个问题是,它给了我这些函数的统计“开销”(不确定是什么意思 – 可能是在函数的进入和退出之间花费的时间？) – 但我真正想要的是堆栈跟踪的日志是顺序的.不确定是否可以为此设置perf – 但绝对可以使用内核模块代码来完成硬件断点.

使用内核模块HW断点

HWDEBUG_STACK中的代码实现了HW断点的设置和处理.如上所述,符号ksym_name(如果未指定)的默认设置是testhrarr_arr,它根本不触发硬件断点.在insmod期间,可以在命令行中指定ksym_name参数;在这里我们可以注意到：

$sudo rmmod testhrarr    # remove module if still loaded
$sudo insmod ./testhrarr.ko ksym=testhrarr_arr[0]

…在/ var / log / syslog中安装了HW Breakpoint for testhrarr_arr [0]的结果(0x(null)); – 这意味着我们不能使用带括号表示法的符号进行数组访问;谢天谢地,这里的空指针只是意味着HW断点将再次不会触发;它不会完全崩溃操作系统:)

但是,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 – 注意如何在代码中专门处理此全局变量,并且需要取消引用,以便获得正确的地址.所以我们这样做：

$sudo rmmod testhrarr    # remove module if still loaded
$sudo insmod ./testhrarr.ko ksym=testhrarr_arr_first

…并且syslog通知：

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HW断点设置为0xedf6c5c0,这是testhrarr_arr [0]的地址.现在,如果我们通过/ proc文件触发驱动程序：

$cat /proc/testhrarr_proc 
testhrarr proc: startup

…我们在syslog中获取：

^{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,]}

…我们得到一个堆栈跟踪正好三次 – 一次在testhrarr_startup期间,两次在testhrarr_timer_function中：一次用于runcount == 0,一次用于runcount == 5,如预期的那样.

嗯,希望这有助于某人,
干杯!

Makefile文件

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 \n",__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\n",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("]\n");
    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,HRTIMER_MODE_REL);
  }
}


static int testhrarr_proc_show(struct seq_file *m,void *v) {
  if (testhrarr_isRunning == 0) {
    seq_printf(m,"testhrarr proc: startup\n");
    testhrarr_startup();
  } else {
    seq_printf(m,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\n",ksym_name);
  dump_stack();
  printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
}
#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\n",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\n",&testhrarr_runcount,&testhrarr_arr,&(testhrarr_arr[0]),testhrarr_arr_first,&testhrarr_timer_function,&my_hrtimer,&my_hrtimer.function);


  proc_create("testhrarr_proc",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\n");
    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)\n",(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)\n",ret_cancel);
  }
  if (hrtimer_active(&my_hrtimer) != 0) {
    ret_cancel = hrtimer_cancel(&my_hrtimer);
    printk(KERN_INFO " testhrarr active hrtimer cancelled: %d (%d)\n",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)\n",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\n",ksym_name);
  #endif
  printk(KERN_INFO "Exit testhrarr\n");
}

module_init(testhrarr_init);
module_exit(testhrarr_exit);

MODULE_LICENSE("GPL");

调试 – 观察Linux内核中的变量(内存地址)更改,并在更改时打印堆栈跟踪？

解决方法

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