About use of dlsym()

DISCUSSION taeung 2 participants 4 messages Aug 8, 2014 – Aug 12, 2014

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taeung

author

2014-08-08 06:29 UTC #0 lore raw

Hello, perf hackers :-)

I'm beginner in perf.
I'm analysing the sequence of function call and how it was written to update 'report' of gtk view.

This is a thread of a command 'perf report --gtk'

1. run_argv()
(in main of perf.c:534)

2. handle_internal_command()
(in run_argv of perf.c:420 )
So far, I've thought this process is to filter what command and option is

3. cmd_report()
(in run_builtin of perf.c:319) by function pointer

4. setup_browser()
(in cmd_report of builtin-report.c:750)

5. setup_gtk_browser()
(in setup_browser of ui/setup.c:74)

6. perf_gtk__init()
(in setup_gtk_browser of ui/setup.c:32)

about number 6, I have a question.

In setup_gtk_browser of ui/setup.c: 28 ~ 32,

28 perf_ui_init = dlsym(perf_gtk_handle, "perf_gtk__init");
29 if (perf_ui_init == NULL)
30 goto out_close;
31
32 if (perf_ui_init() == 0)
33 return 0;
34

Why not call directly 'perf_gtk__init()' ?
Why call the function by function pointer(perf_ui_init) after it is gotten by 'dlsym()' ? Why use 'dlsym()' ?
Is it better than calling directly the function ?

- Taeung -

Taeung

author

2014-08-09 13:39 UTC #1 lore raw

Sorry for my poor question.

I didn't know that 'dlopen()', 'dlsym()', 'dlclose()' for DL(Dynamic Library). But I know it.

- Taeung -

Quoted 44 lines · taeung

Hello, perf hackers :-)
I'm beginner in perf.
I'm analysing the sequence of function call and how it was written to update 'report' of gtk view.
This is a thread of a command 'perf report --gtk'
1. run_argv()
(in main of perf.c:534)
2. handle_internal_command()
(in run_argv of perf.c:420 )
So far, I've thought this process is to filter what command and option is
3. cmd_report()
(in run_builtin of perf.c:319) by function pointer
4. setup_browser()
(in cmd_report of builtin-report.c:750)
5. setup_gtk_browser()
(in setup_browser of ui/setup.c:74)
6. perf_gtk__init()
(in setup_gtk_browser of ui/setup.c:32)
about number 6, I have a question.
In setup_gtk_browser of ui/setup.c: 28 ~ 32,
28 perf_ui_init = dlsym(perf_gtk_handle, "perf_gtk__init");
29 if (perf_ui_init == NULL)
30 goto out_close;
31
32 if (perf_ui_init() == 0)
33 return 0;
34
Why not call directly 'perf_gtk__init()' ?
Why call the function by function pointer(perf_ui_init) after it is gotten by 'dlsym()' ? Why use 'dlsym()' ?
Is it better than calling directly the function ?
- Taeung -

Namhyung Kim

2014-08-11 07:25 UTC #2 lore raw

In reply to taeung

Hi taeung,

Quoted 39 lines · taeung

Hello, perf hackers :-)
I'm beginner in perf.
I'm analysing the sequence of function call and how it was written to update 'report' of gtk view.
This is a thread of a command 'perf report --gtk'
1. run_argv()
(in main of perf.c:534)
2. handle_internal_command()
(in run_argv of perf.c:420 )
So far, I've thought this process is to filter what command and option is
3. cmd_report()
(in run_builtin of perf.c:319) by function pointer
4. setup_browser()
(in cmd_report of builtin-report.c:750)
5. setup_gtk_browser()
(in setup_browser of ui/setup.c:74)
6. perf_gtk__init()
(in setup_gtk_browser of ui/setup.c:32)
about number 6, I have a question.
In setup_gtk_browser of ui/setup.c: 28 ~ 32,
28 perf_ui_init = dlsym(perf_gtk_handle, "perf_gtk__init");
29 if (perf_ui_init == NULL)
30 goto out_close;
31
32 if (perf_ui_init() == 0)
33 return 0;
34

Quoted 5 lines

Why not call directly 'perf_gtk__init()' ?
Why call the function by function pointer(perf_ui_init) after it is gotten by 'dlsym()' ?
Why use 'dlsym()' ?
Is it better than calling directly the function ?

It was because many perf users wanted to reduce dependency in the main perf binary as they hardly/never use the GTK ui. Although it can be disabled with NO_GTK2=1 when invoking make, they're just too lazy to do that. :)

Please see https://lkml.org/lkml/2013/8/4/154 .

Thanks,
Namhyung

taeung

author

2014-08-12 05:51 UTC #3 lore raw

Thanks, Namhyung Kim

I've understood what you mean.
And I've read the patch which you told me.

There are the different between current version and the patch. In current version, 'perfgtk', gtkstub.c aren't used. and GUI_OBJS was changed into GTK_OBJS.

I thought about the reason why DL(Dynamic Library) is used instead of several ways of the patch. But I need to look over more..

Thank you, again.

- Taeung -

Quoted 56 lines · Namhyung Kim

Hi taeung,
Quoted 39 lines · taeung
Hello, perf hackers :-)
I'm beginner in perf.
I'm analysing the sequence of function call and how it was written to update 'report' of gtk view.
This is a thread of a command 'perf report --gtk'
1. run_argv()
(in main of perf.c:534)
2. handle_internal_command()
(in run_argv of perf.c:420 )
So far, I've thought this process is to filter what command and option is
3. cmd_report()
(in run_builtin of perf.c:319) by function pointer
4. setup_browser()
(in cmd_report of builtin-report.c:750)
5. setup_gtk_browser()
(in setup_browser of ui/setup.c:74)
6. perf_gtk__init()
(in setup_gtk_browser of ui/setup.c:32)
about number 6, I have a question.
In setup_gtk_browser of ui/setup.c: 28 ~ 32,
  28         perf_ui_init = dlsym(perf_gtk_handle, "perf_gtk__init");
  29         if (perf_ui_init == NULL)
  30                 goto out_close;
  31
  32         if (perf_ui_init() == 0)
  33                 return 0;
  34
Quoted 5 lines
Why not call directly 'perf_gtk__init()' ?
Why call the function by function pointer(perf_ui_init) after it is gotten by 'dlsym()' ?
Why use 'dlsym()' ?
Is it better than calling directly the function ?
It was because many perf users wanted to reduce dependency in the main perf binary as they hardly/never use the GTK ui. Although it can be disabled with NO_GTK2=1 when invoking make, they're just too lazy to do that. :)
Please see https://lkml.org/lkml/2013/8/4/154 .
Thanks,
Namhyung