c++ - Systemtap 简单用户空间示例(功能跟踪，Ubuntu)？

Question

(我花了很多时间让它工作，所以我想我应该记录它 - 首先，正式地把它作为一个问题):

在用户空间应用程序中是否有systemtap 探测/跟踪功能的简单示例，最好是在 C++ 中？我的系统是 Ubuntu 14.04:

$ uname -a
Linux mypc 4.2.0-42-generic #49~14.04.1-Ubuntu SMP Wed Jun 29 20:22:11 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
$ g++ --version
g++ (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4 ...
$ stap --version
Systemtap translator/driver (version 2.3/0.158, Debian version 2.3-1ubuntu1.4 (trusty))

Answer 1

好的，所以这并不是微不足道的——首先，我以某种方式在 Ubuntu 14.04 上得到了一个(更新的)内核 4.2.0；显然是 systemtap Ubuntu 14.04 附带的内核对于该内核来说太旧了(见下文)。这意味着我必须构建 systemtap来自源头——这是我的程序:

cd /path/to/src
git clone git://sourceware.org/git/elfutils.git elfutils_git
git clone git://sourceware.org/git/systemtap.git systemtap_git
cd systemtap_git
./configure --with-elfutils=/path/to/src/elfutils_git --prefix=/path/to/src/systemtap_git/local --enable-docs=no
make
make install
# after this, there are `stap` executables in: 
#  /path/to/src/systemtap_git/stap
#  /path/to/src/systemtap_git/local/bin/stap

事情是这样的:

• 你不应该 build elfutils分开，然后 systemtap - 你应该改为传递 elfutils源目录到 --with-elfutils的 systemtap的 configure ，然后将 configure并构建elfutils以及。
• 你必须做make install的 systemtap ，即使它在非系统/私有(private)(本地)目录中! - 否则，会发生一些错误(不幸的是，没有记录它们)

构建后，stap报告版本:

$ ./stap --version
Systemtap translator/driver (version 3.2/0.170, commit release-3.1-331-g0efba6fc74c8 + changes) ...

好的，所以我找到了一个基本的 Fibonacci C++ 示例进行分析，我稍微修改了一下，并调用了 /tmp/<b>fibo.cpp</b> :

// based on: http://www.cplusplus.com/articles/LT75fSEw/
#include <iostream>

using namespace std;

class Fibonacci{
public:
  int a, b, c;
  void generate(int);
  void doFibonacciStep(int);
};

void Fibonacci::doFibonacciStep(int istep){
  c = a + b;
  cout << "  istep: " << istep << " c: " << c << endl;
  a = b;
  b = c;
}

void Fibonacci::generate(int n){
  a = 0; b = 1;
  cout << " Start: a "<< a << " b " << b << endl;
  for(int i=1; i<= n-2; i++){
    doFibonacciStep(i);
  }
}

int main()
{
  cout << "Hello world! Fibonacci series" << endl;
  cout << "Enter number of items you need in the series: ";
  int n;
  cin  >> n;
  Fibonacci fibonacci;
  fibonacci.generate(n);
  return 0;
}

首先我尝试这样编译它:

cd /tmp
g++ -g fibo.cpp -o fibo.exe

现在，我们要做的第一件事是找出可执行文件中哪些函数可用于探测；为此，我们可以使用 stap -L (注意，这里我仍然使用旧的 Ubuntu 14.04 系统 stap ):

$ stap -L 'process("/tmp/fibo.exe").function("*").call'
process("/tmp/fibo.exe").function("_GLOBAL__sub_I__ZN9Fibonacci15doFibonacciStepEi").call
process("/tmp/fibo.exe").function("__static_initialization_and_destruction_0").call $__initialize_p:int $__priority:int
process("/tmp/fibo.exe").function("doFibonacciStep@/tmp/fibo.cpp:13").call $this:class Fibonacci* const $istep:int
process("/tmp/fibo.exe").function("generate@/tmp/fibo.cpp:20").call $this:class Fibonacci* const $n:int
process("/tmp/fibo.exe").function("main@/tmp/fibo.cpp:28").call

很好 - 所以我想探测/追踪 doFibonacciStep及其输入参数 istep .所以我从命令行尝试:

$ sudo stap -e 'probe process("/tmp/fibo.exe").function("Fibonacci::doFibonacciStep").call { printf("stap do step: %d\n", $istep) }' -c /tmp/fibo.exe 
WARNING: "__tracepoint_sched_process_fork" [/tmp/stap51A5tV/stap_ab5b824c79b38b5207910696c49c4e22_1760.ko] undefined!
WARNING: "__tracepoint_sys_exit" [/tmp/stap51A5tV/stap_ab5b824c79b38b5207910696c49c4e22_1760.ko] undefined!
WARNING: "__tracepoint_sys_enter" [/tmp/stap51A5tV/stap_ab5b824c79b38b5207910696c49c4e22_1760.ko] undefined!
WARNING: "__tracepoint_sched_process_exec" [/tmp/stap51A5tV/stap_ab5b824c79b38b5207910696c49c4e22_1760.ko] undefined!
WARNING: "__tracepoint_sched_process_exit" [/tmp/stap51A5tV/stap_ab5b824c79b38b5207910696c49c4e22_1760.ko] undefined!
ERROR: Couldn't insert module '/tmp/stap51A5tV/stap_ab5b824c79b38b5207910696c49c4e22_1760.ko': Unknown symbol in module
WARNING: /usr/bin/staprun exited with status: 1
Pass 5: run failed.  [man error::pass5]
Tip: /usr/share/doc/systemtap/README.Debian should help you get started.
$ sudo stap -e 'probe process("/tmp/fibo.exe").function("Fibonacci::doFibonacciStep").call { printf("stap do step: %d\n", $istep) }' -c /tmp/fibo.exe 
ERROR: Couldn't insert module '/tmp/stapmo60OW/stap_ab5b824c79b38b5207910696c49c4e22_1760.ko': Unknown symbol in module
WARNING: /usr/bin/staprun exited with status: 1
Pass 5: run failed.  [man error::pass5]

哎呀，像这样的错误 - 不好。本帖"__tracepoint_sched_process_fork undefined" when run systemstap script基本上解释了 stap版本对于我拥有的内核来说太旧了——这需要从源代码(上面)构建。那么现在让我们看看新的 stap -L 是如何产生的。作品:

$ /path/to/src/systemtap_git/stap -L 'process("/tmp/fibo.exe").function("*").call'
process("/tmp/fibo.exe").function("_GLOBAL__sub_I__ZN9Fibonacci15doFibonacciStepEi@/tmp/fibo.cpp:37").call
process("/tmp/fibo.exe").function("__do_global_dtors_aux").call
process("/tmp/fibo.exe").function("__libc_csu_fini").call
process("/tmp/fibo.exe").function("__libc_csu_init").call
process("/tmp/fibo.exe").function("__static_initialization_and_destruction_0@/tmp/fibo.cpp:37").call $__initialize_p:int $__priority:int
process("/tmp/fibo.exe").function("_fini").call
process("/tmp/fibo.exe").function("_init").call
process("/tmp/fibo.exe").function("_start").call
process("/tmp/fibo.exe").function("deregister_tm_clones").call
process("/tmp/fibo.exe").function("doFibonacciStep@/tmp/fibo.cpp:13").call $this:class Fibonacci* const $istep:int
process("/tmp/fibo.exe").function("frame_dummy").call
process("/tmp/fibo.exe").function("generate@/tmp/fibo.cpp:20").call $this:class Fibonacci* const $n:int
process("/tmp/fibo.exe").function("main@/tmp/fibo.cpp:28").call
process("/tmp/fibo.exe").function("register_tm_clones").call

很好，这已经比旧版本更冗长了。不管怎样，我想调查一下 doFibonacciStep函数及其输入参数，此处为 $istep .所以我在命令行上写了这个:

$ sudo /path/to/src/systemtap_git/stap -e 'probe process("/tmp/fibo.exe").function("Fibonacci::doFibonacciStep").call { printf("stap do step: %d\n", $istep) }' -c /tmp/fibo.exe 
semantic error: while processing probe process("/tmp/fibo.exe").function("Fibonacci::doFibonacciStep@/tmp/fibo.cpp:13").call from: process("/tmp/fibo.exe").function("Fibonacci::doFibonacciStep").call

semantic error: No cfa_ops supplied, but needed by DW_OP_call_frame_cfa: identifier '$istep' at <input>:1:107
        source: probe process("/tmp/fibo.exe").function("Fibonacci::doFibonacciStep").call { printf("stap do step: %d\n", $istep) }

Pass 2: analysis failed.  [man error::pass2]

糟糕 - 一个令人讨厌的错误，并没有真正告诉我任何事情 - 关于此错误的错误报告很少(而且大部分来自 2010 年)。所以我正要卡在这里，不知何故，我想起前几天，我用 -gdwarf-2 编译了一些程序。 (出于我现在忘记的原因)；所以我想我会尝试一下 - 哇天知道，它现在真的开始工作了:

$ g++ -gdwarf-2 fibo.cpp -o fibo.exe
$ sudo /path/to/src/systemtap_git/stap -e 'probe process("/tmp/fibo.exe").function("Fibonacci::doFibonacciStep").call { printf("stap do step: %d\n", $istep) }' -c /tmp/fibo.exe 
Hello world! Fibonacci series
Enter number of items you need in the series: 5
 Start: a 0 b 1
  istep: 1 c: 1
  istep: 2 c: 2
  istep: 3 c: 3
stap do step: 1
stap do step: 2
stap do step: 3

不错!请注意 stap打印实际上是在程序完成后 打印的(也就是说，它们不会与它们出现的实际程序输出交错)。

我们可以编写一个脚本，而不是直接在命令行上指定探测点和行为 - 所以这里是 check-do-step.stp - 这里有一些额外的东西:

#!/usr/bin/env stap

global stringone = "Testing String One"
global stringtwo = "Testing String Two"

probe begin {
  printf("begin: %s\n", stringone)
  #exit() # must have; else probe end runs only upon Ctrl-C if we only have `begin` and `end` probes!
}

probe process(
  "/tmp/fibo.exe"
).function(
  "Fibonacci::doFibonacciStep"
).call {
  printf("stap do step: %d\n", $istep)
}

probe end {
  newstr = "We Are " . stringtwo . " And We're Done" # string concat
  printf("%s\n", newstr)
}

...使用此脚本，我们的调用和结果如下所示:

$ sudo /path/to/src/systemtap_git/stap check-do-step.stp -c /tmp/fibo.exe
Hello world! Fibonacci series
Enter number of items you need in the series: begin: Testing String One
6
 Start: a 0 b 1
  istep: 1 c: 1
  istep: 2 c: 2
  istep: 3 c: 3
  istep: 4 c: 5
stap do step: 1
stap do step: 2
stap do step: 3
stap do step: 4
We Are Testing String Two And We're Done

再次注意 - begin: Testing ...字符串并没有像我们预期的那样在一开始就命中，而是在程序已经开始生成输出之后才命中。

好吧，我想就是这样 - 对我来说当然足够了，举个简单的例子......