gprof 没有输出 [英] gprof gives no output

问题描述

我正在尝试使用 gprof 来分析我正在开发的一些数字代码，但是 gprof 似乎无法从我的程序中收集数据.这是我的命令行:

I am trying to use gprof to profile some numerical code I am developing, but gprof seems to fail to collect data from my program. Here is my command line:

g++ -Wall -O3 -g -pg -o fftw_test fftw_test.cpp -lfftw3 -lfftw3_threads -lm && ./fftw_test

gmon.out 文件已创建，但似乎没有数据.当我跑

The gmon.out file is created, but it seems to have no data. When i run

gprof -b fftw_test gmon.out > gprof.out

我得到的是

Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls  Ts/call  Ts/call  name    


                        Call graph


granularity: each sample hit covers 2 byte(s) no time propagated

index % time    self  children    called     name


Index by function name

有什么见解吗?

代码做了很多事情，它不只是调用 FFTW 例程.它具有计算某些复数系数的函数、将输入数据乘以这些系数的函数等.

The code does a lot of stuff, it does not simply call FFTW routines. It has functions that compute certain complex coefficients, functions that multiply input data by these coefficients, and so on.

编辑.:包括示例代码和结果.

Edit.: Including example code and results.

#include <cstdlib>
#include <ctime>

int main()
{
   std::srand( std::time( 0 ) );

   double sum = 0.0;

   for ( int i = 0; i < RAND_MAX; ++i )
      sum += std::rand() / ( double ) RAND_MAX;

   std::cout << sum << '\n';

   return 0;
}

命令行:

$ g++ -Wall -O3 -g -pg -o gprof_test gprof_test.cpp && ./gprof_test
1.07374e+09
$ gprof -b gprof_test gmon.out > gprof.out
$ cat gprof.out

结果:

Flat profile:

Each sample counts as 0.01 seconds.
 no time accumulated

  %   cumulative   self              self     total           
 time   seconds   seconds    calls  Ts/call  Ts/call  name    


                        Call graph


granularity: each sample hit covers 2 byte(s) no time propagated

index % time    self  children    called     name


Index by function name

就是这样.

推荐答案

如果您使用 gcc 6，您很可能会遇到 this 错误(请注意，该错误并非特定于 Debian，而是取决于 gcc 的构建方式).一种解决方法是使用 `-no-pie' 选项进行编译，该选项会禁用与位置无关的代码生成.

If you're using gcc 6, you're most likely running into this bug (note that the bug is not specific to Debian but depends on how gcc was built). A workaround is simply to compile using the `-no-pie' option which disables position-independent code generation.

这个 是一个好的开始.

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