Re: Problems on glibc UTRACE

[Shane Wayne <zx0319 at gmail dot com>]

2014-11-22 0:40 GMT+08:00 David Smith <dsmith@redhat.com>:
> On 11/20/2014 08:25 PM, Shane Wayne wrote:
>> I've recently tap into malloc function of glibc, but I've encounter
>> some problems.
>> Firstly, I have install systemtap and glibc-dbg on Ubuntu 14.04(with
>> kernel 3.13 and UTRACE kernel flag default on).
>
> What UTRACE kernel flag are you talking about? In the past (RHEL5 &
> RHEL6), there was an in-kernel utrace. Now utrace functionality is built
> on top of kernel tracepoints.
Sorry, I got it wrong, it was UPROBES flag, in /boot/config-3.13.0-40-generic
42:
CONFIG_ARCH_SUPPORTS_UPROBES=y
CONFIG_DEFCONFIG_LIST="/lib/modules/$UNAME_RELEASE/.config"
CONFIG_IRQ_WORK=y
CONFIG_BUILDTIME_EXTABLE_SORT=y

But in /boot/config-3.2.0-61-generic in Ubuntu dist there is no flags
related to UPROBES

>
>> The result show that, I can tap into
>> process("/lib/x86_64-linux-gnu/libc.so.6").function("malloc"), BUT,
>> the question is that, I can't get the right $bytes in this system, the
>> value I've got always like an pointer value start with 0x7f****. I've
>> tried the script on my own micro benchmark, with a single malloc
>> function invoke, the result also show that I can't get the right
>> parameters out, what's more, my micro benchmark triggered the tap
>> TWICE.
>> Secondly, I migrate to CentOS 6.6, with kernel
>> 2.6.32-504.1.3.el6.x86_64 and UTRACE kernel flag default on, at this
>> time, I can get the right parameter $bytes out, but in my own micro
>> benchmark, the twice triggered problem also appear.
>
> Do you have glibc debuginfo installed on your Ubuntu system? Can you
> show us your systemtap script?
>
I think the following packets was related to Glibc:
ii  libc6:amd64                           2.19-0ubuntu6.3
              amd64        Embedded GNU C Library: Shared libraries
ii  libc6-dbg:amd64                       2.19-0ubuntu6.3
              amd64        Embedded GNU C Library: detached debugging
symbols
ii  libc6-dev:amd64                       2.19-0ubuntu6.3
              amd64        Embedded GNU C Library: Development
Libraries and Header Files

I think libc60dbg:amd64 was the debuginfo?

The script was:
probe process("/lib/x86_64-linux-gnu/libc.so.6").function("malloc").return
{
  if(execname()==@1)
  {
    t = gettimeofday_us()
    printf("malloc\t%s\treturn=0x%x\tPID:%d\tTID:%d\tCPU:%d\tSTART:%d\tEND:%d\n",$$parms,$return,pid(),tid(),cpu(),@entry(gettimeofday_us()),t)
  }
}

And the result like:
malloc  bytes=0x7ffff45c7440    return=0x951010 PID:21274
TID:21274  CPU:16   START:1416809393964834  END:1416809393964865
malloc  bytes=0x7ffff45c7440    return=0x951010 PID:21274
TID:21274  CPU:16   START:1416809393964737  END:1416809393964874

The source file was like:
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  void *ptr;
  int i;

  getchar();
  ptr = malloc(10);
  printf("%x",ptr);
  getchar();
  return 0;
}

The result also shows the twice trigger problem
Thanks for your reply~ David Smith~



> --
> David Smith
> dsmith@redhat.com
> Red Hat
> http://www.redhat.com
> 256.217.0141 (direct)
> 256.837.0057 (fax)



-- 
------------------------------------------------------------
ZHANG Xiao

The Institute of Computer Software Engineering and Theory in Xi'an
Jiaotong University
Master-and-Doctoral Program Student

ACM Student Member
CCF Student Member
IEEE Computer Society Sister Society Associate Member

Xi'an Jiaotong University
Bachelor of Engineering in Computer Science and Technology

The Chinese University of Hong Kong
International Asia Study Program in CS/CE/EE/IE