perf can find symbol in the kernel ,but can not find symbol in my program. How to fix it?

Question

you may have read this question: how can i get perf to find symbols in my program

1)my question is:

when I use perf report , it gives a result like this:

    # Overhead  Command      Shared Object                    Symbol
    #   .  .  
    #
        99.59%     test  test               [.] 0x000003d4          
         0.21%     test  [kernel.kallsyms]  [k] __do_fault          
         0.10%     test  [kernel.kallsyms]  [k] run_timer_softirq   
         0.10%     test  [kernel.kallsyms]  [k] __update_cpu_load   
         0.01%     test  [kernel.kallsyms]  [k] set_task_comm       
         0.00%     test  [kernel.kallsyms]  [k] intel_pmu_enable_all

That is: the perf can find symbol in kernel but cannot find symbol in my program.

my program is here:

     void longa() 
      { 
         int i,j; 
         for(i = 0; i < 1000000; i++) 
        j=i; //am I silly or crazy? I feel boring and desperate. 
      } 


     void foo2() 
     { 
       int i; 
       for(i=0 ; i < 10; i++) 
        longa(); 
     } 

     void foo1() 
     { 
       int i; 
       for(i = 0; i< 100; i++) 
          longa(); 
     } 

    int main(void) 
     { 
       foo1(); 
       foo2(); 
     } 

2)I have compile the program like:

gcc test.c -g -o test

My env: os:ubuntu kernel:3.10.9

Answer 1

Today, when I run perf test, I got a message saying vmlinux symtab matches kallsyms: Failed.

When I was looking for the reason, I found that the reason is that the value of /proc/sys/kernel/kptr_restrict is 1. When we set it to 0, we will get the symbol in our program.

Answer 2

There are 2 possible sources of the problem:

• Your perf tool was compiled without elfutils support.
• Your perf tool cannot find libelf.so library on your target.