Hi all,
in order to get to know better how things in ns-2 work and where to start
placing my own implementation, I'd like to use gdb and the tcl debugger
and step through the initialisation process of ns-2 one by one.
Despite many attempts of doing this, gdb keeps refusing to decent into
function calls using the "step" command but just rushes to the end of the
program. I've searched for answers to this problem in the mailing-list
archives which basically claim that one just needs to enable debugging
info to do this.
So what I did was this: I modified the install script and added
"--enable-debug" to the OTcl, Tclcl, ns, and nam build processes and
"--enable-symbols" to tcl and tk. I re-compiled over and over without
success as gdb would continue doing what I do not want it to do.
Here's a gdb output excerpt:
~/sa/ns2/ns-allinone/ns-2.30$ gdb ns
[legal stuff]
This GDB was configured as "i486-linux-gnu"...Using host libthread_db
library "/lib/tls/i686/cmov/libthread_db.so.1".
(gdb) list main
60 *
61
*----------------------------------------------------------------------
62 */
63
64 int
65 main(int argc, char **argv)
66 {
67 Tcl_Main(argc, argv, Tcl_AppInit);
68 return 0; /* Needed only to prevent compiler
warning. */
69 }
(gdb) b main
Breakpoint 1 at 0x804d161: file common/tclAppInit.cc, line 67.
(gdb) run "~/sa/ns2/ns-allinone-2.30/scenarios/testing/example3.tcl"
Starting program: /home/<my user name>/sa/ns2/ns-allinone-2.30/ns-2.30/ns
"/home/<my user name>/ns2/ns-allinone-2.30/scenarios/testing/example3.tcl"
Breakpoint 1, main (argc=2, argv=0xbfdd1254) at common/tclAppInit.cc:67
67 Tcl_Main(argc, argv, Tcl_AppInit);
(gdb) s
Program exited normally.
(gdb)
As far as I can see, I've succeeded in adding debugging symbols since I
can use the "list" command to see where I'm at in the code. Prior to
inserting all the debugging switches, it would give an error.
To make sure, I've also compiled and incorporated tcl-debug-2.0 into ns-2
which verifiably works but did not affect gdb's behaviour.
In addition, I've cleared my PATH environment variable to only include the
ns-2-specific paths and used full pathnames for everything else (like gdb)
because I suspected my globally installed copy of tk to interfer in this
matter. This wasn't true, however.
When I step through the code using stepi (instruction-level stepping) I
can perfectly see all function calls including instruction pointer
arithmetics. This seems to derive from machine-level code, however, and
therefore isn't very useful to me.
At this point, I'm really lost. I believe the list archive postings on
this issue are not more recent than 2003 so I suppose it's just me having
this problem but I absolutely cannot see what else to do.
I'm using ns-2 allinone-2.30, gdb 6.4.90-debian, and gcc 4.1.2 under
Ubuntu 6.10 (Edgy Eft).
Glad for any help!
Cheers,
--Timo
