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Date:	Thu, 19 Jun 2014 07:39:42 +0000
From:	Tony Lu <zlu@...era.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tony Lu <zlu@...era.com>, Chris Metcalf <cmetcalf@...era.com>
Subject: [BUG] perf: can not resolve symbols for forked threads

Hi

I got the below output that shows perf can not resolve symbols for forked threads. I did a system-wide collection from all CPUs after the application hello run.

-bash-4.1$ ./perf --version
perf version 3.16.rc1.ge99cfa2
-bash-4.1$ ./hello & ./perf record -a sleep 5
-bash-4.1$ ./perf report
# Overhead      Command       Shared Object                         Symbol
# ........  ...........  ..................  .............................
#
    54.77%        hello  [unknown]           [.] 0x0000000000400610       
    28.59%        hello  [unknown]           [.] 0x0000000000400615       
    16.53%        hello  [unknown]           [.] 0x000000000040061f       
     0.01%        hello  [kernel.kallsyms]   [k] __rcu_process_callbacks  
     0.01%         perf  [kernel.kallsyms]   [k] copy_user_generic_string 
     0.01%        sleep  [kernel.kallsyms]   [k] filemap_fault
....

/***************************************************************************** FILE: hello.c
** DESCRIPTION:
** A "hello world" Pthreads program to trigger this bug.
***************************************************************************/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define NUM_THREADS     5

void foo(void)
{
  long i = 1000000000;
  while (i--) {
    ;
  }
}

void *PrintHello(void *threadid)
{
   long tid;
   tid = (long)threadid;
   printf("Hello World! It's me, thread #%ld!\n", tid);
   foo();
   pthread_exit(NULL);
}

int main(int argc, char *argv[])
{
   pthread_t threads[NUM_THREADS];
   int rc;
   long t;
   for(t=0;t<NUM_THREADS;t++){
     printf("In main: creating thread %ld\n", t);
     rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
     if (rc){
       printf("ERROR; return code from pthread_create() is %d\n", rc);
       exit(-1);
       }
     }

   /* Last thing that main() should do */
   pthread_exit(NULL);
}

Thanks
-Tony
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