Performance, stepping into source for shared libs

Performance, stepping into source for shared libs

[Arne Steinarson]

I have a C++ app with just a small main.cpp. However
it links into large libraries (GTK and framework on
top of GTK, running i386 Linux).

Most times when I open the app in GDB I will have
quite a delay when stepping into a lower function the
first time. CPU usage goes to 100% and it takes
between 10 and 60 seconds before I can see the new
source line. The next time stepping into the same
function, it happens without delay.

Stepping into a new function in another source file
(possibly in the same directory as the last one) I
again have the long delay.

It seems to happen mostly with functions in shared
libraries.

First I thought it was the IDE (Eclipse) to blame. So
I tried in GDB standalone, command line version. Same
delay!

Is there some way to reduce these waits?

What is GDB up to during this time (it doesn't give
any feedback)?

Regards
// ATS


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Re: Performance, stepping into source for shared libs

[Nick Roberts]

Arne Steinarson writes:
 > I have a C++ app with just a small main.cpp. However
 > it links into large libraries (GTK and framework on
 > top of GTK, running i386 Linux).
 > 
 > Most times when I open the app in GDB I will have
 > quite a delay when stepping into a lower function the
 > first time. CPU usage goes to 100% and it takes
 > between 10 and 60 seconds before I can see the new
 > source line. The next time stepping into the same
 > function, it happens without delay.
 > 
 > Stepping into a new function in another source file
 > (possibly in the same directory as the last one) I
 > again have the long delay.
 > 
 > It seems to happen mostly with functions in shared
 > libraries.
 > 
 > First I thought it was the IDE (Eclipse) to blame. So
 > I tried in GDB standalone, command line version. Same
 > delay!
 > 
 > Is there some way to reduce these waits?

What happens if you do

  (gdb) set auto-solib-add off

first?

-- 
Nick                                           http://www.inet.net.nz/~nickrob

Re: Performance, stepping into source for shared libs

[Daniel Jacobowitz]

On Mon, Jul 02, 2007 at 01:34:05AM +0200, Arne Steinarson wrote:
> Is there some way to reduce these waits?
> 
> What is GDB up to during this time (it doesn't give
> any feedback)?

It's hard to say.  It could be any of several things.  My first guess
is that it is stepping its way through the dynamic symbol lookup
process; under some conditions it can use a breakpoint instead, under
others it can not.

-- 
Daniel Jacobowitz
CodeSourcery

Re: Performance, stepping into source for shared libs

[Arne Steinarson]

After doing some searching, I found this thread from
January: 

http://www.ecos.sourceware.org/ml/gdb/2007-01/msg00020.html

It's the same problem I have, I'm also on Debian
system (Ubuntu), with GDB 6.6. Apparently GDB is
single stepping through loading and resolving every
symbol of the shared library. 

Setting LD_BIND_NOW to non-empty value solves the
problem.

Hoping a fix of this issue could make it into future
release. 

Regards
// Arne S.


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