How to store function-name and its return values while program runs

How to store function-name and its return values while program runs

[Sandeep222]

As we proceed with debugging a program, if I need to know the order of
functions being executed by printing on screen along with their return
values when a 'run' command or 'next' command is executed, how can i
proceed? I went thru frame.c but all the function seem to execute only when
a command is executed in the gdb. Plz help. 
Reg, 
Sandeep
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Re: How to store function-name and its return values while program runs

[Gaius Mulley]

Sandeep222 <sandeep.srikumar@honeywell.com> writes:

> As we proceed with debugging a program, if I need to know the order of
> functions being executed by printing on screen along with their return
> values when a 'run' command or 'next' command is executed, how can i
> proceed? I went thru frame.c but all the function seem to execute only when
> a command is executed in the gdb. Plz help. 
> Reg, 
> Sandeep

set a breakpoint at each of the functions of interest.

(gdb) break function1
(gdb) break function2

etc

now run the program

(gdb) run

when gdb hits a breakpoint you can finish the function and
print the result via:

(gdb) fin

regards,
Gaius

Re: How to store function-name and its return values while program runs

[Michael Snyder]

Gaius Mulley wrote:
> Sandeep222 <sandeep.srikumar@honeywell.com> writes:
> 
>> As we proceed with debugging a program, if I need to know the order of
>> functions being executed by printing on screen along with their return
>> values when a 'run' command or 'next' command is executed, how can i
>> proceed? I went thru frame.c but all the function seem to execute only when
>> a command is executed in the gdb. Plz help. 
>> Reg, 
>> Sandeep
> 
> set a breakpoint at each of the functions of interest.
> 
> (gdb) break function1
> (gdb) break function2
> 
> etc
> 
> now run the program
> 
> (gdb) run
> 
> when gdb hits a breakpoint you can finish the function and
> print the result via:
> 
> (gdb) fin

And indeed, you can make that automatic by attaching the
commands to the breakpoints:

(gdb) break function1
(gdb) commands
 > finish
 > continue
 > end
(gdb)

Re: How to store function-name and its return values while program runs

[Paul Pluzhnikov]

On Fri, Nov 21, 2008 at 11:04 AM, Michael Snyder <msnyder@vmware.com> wrote:

> (gdb) break function1
> (gdb) commands
>> finish
>> continue
>> end
> (gdb)

I wished many times that above worked, but it doesn't: 'finish'
appears to interrupt flow of script, and subsequent commands are
never executed:

  cat t.c
  int foo() { return 42; }
  int main() { return foo(); }

  gcc -g t.c

  gdb64-cvs ./a.out
  GNU gdb (GDB) 6.8.50.20081118-cvs
  Copyright (C) 2008 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
  This is free software: you are free to change and redistribute it.
  There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
  and "show warranty" for details.
  This GDB was configured as "x86_64-unknown-linux-gnu".
  For bug reporting instructions, please see:
  <http://www.gnu.org/software/gdb/bugs/>...
  (gdb) b foo
  Breakpoint 1 at 0x400310: file t.c, line 1.
  (gdb) commands 1
  >finish
  >print/a $pc
  >continue
  >end
  (gdb) r

  Breakpoint 1, foo () at t.c:1
  1       int foo() { return 42; }
  0x0000000000400325 in main () at t.c:2
  2       int main() { return foo(); }
  Value returned is $1 = 42

# Neither 'print/a $pc' nor 'continue' executed :(

  (gdb) q



Is this a bug?

-- 
Paul Pluzhnikov

Re: How to store function-name and its return values while program runs

[Joel Brobecker]

> I wished many times that above worked, but it doesn't: 'finish'
> appears to interrupt flow of script, and subsequent commands are
> never executed:
[...]
> Is this a bug?

It actually isn't. The manual tries to explain why:

> Any other commands in the command list, after a command that resumes
> execution, are ignored. This is because any time you resume execution
> (even with a simple next or step), you may encounter another
> breakpoint--which could have its own command list, leading to
> ambiguities about which list to execute.

Most of the users at AdaCore view this as a limitation, but I haven't
really had the energy to look at improving this.

-- 
Joel

Re: How to store function-name and its return values while program runs

[Michael Snyder]

Joel Brobecker wrote:
>> I wished many times that above worked, but it doesn't: 'finish'
>> appears to interrupt flow of script, and subsequent commands are
>> never executed:
> [...]
>> Is this a bug?
> 
> It actually isn't. The manual tries to explain why:
> 
>> Any other commands in the command list, after a command that resumes
>> execution, are ignored. This is because any time you resume execution
>> (even with a simple next or step), you may encounter another
>> breakpoint--which could have its own command list, leading to
>> ambiguities about which list to execute.
> 
> Most of the users at AdaCore view this as a limitation, but I haven't
> really had the energy to look at improving this.

Mumble.  I'm sorry -- of course I knew about that, but I
must have dreamed that somebody had done something about it
a while back...

Re: How to store function-name and its return values while program runs

[Joel Brobecker]

> Mumble.  I'm sorry -- of course I knew about that, but I
> must have dreamed that somebody had done something about it
> a while back...

I *think* that what was done sometime ago was improve the situation
with function calls. An inferior function call technically restarts
the inferior, but they don't interrupt the command list anymore.

-- 
Joel

Re: How to store function-name and its return values while program runs

[Michael Snyder]

Paul Pluzhnikov wrote:
> On Fri, Nov 21, 2008 at 11:04 AM, Michael Snyder <msnyder@vmware.com> wrote:
> 
>> (gdb) break function1
>> (gdb) commands
>>> finish
>>> continue
>>> end
>> (gdb)
> 
> I wished many times that above worked, but it doesn't: 'finish'
> appears to interrupt flow of script, and subsequent commands are
> never executed:

Am I halucinating?  I thought we fixed that a long time ago.