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Introduction:
This document is to help those Mac and Windows people debug Mozilla
on Linux. This is a work in progress.
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How do I debug 5.0 on Linux?
$ cd mozilla/dist/bin
$ ./mozilla-apprunner.sh -g
If you are new to debugging on Linux, I recommend using ddd.
ddd is a graphical debugger that runs on top of gdb. You may still
find yourself doing gdb command from within ddd.
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How do I use ddd / gdb?
Some docs to get started:
http://www.gnu.org/manual/gdb-4.17/html_mono/gdb.html
http://www.cs.tu-bs.de/softech/ddd/ddd-tips.html
http://www.cs.tu-bs.de/softech/ddd/ddd-faq.html
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The debugger (gdb/ddd) is slow. How can I make it faster?
Add this line to your $HOME/.gdbinit file:
set auto-solib-add 0
This will cause gdb to lazily read symbol tables. (If you are using this option with glibc 2.1, please see What should I do about the SIG32 I'm getting in RH 6.0?)
Example:
I'm debugging apprunner. I interrupt the process.
Looking at the stack trace, I see this:
(gdb) where
#0 0x4085e7d0 in ?? () from /lib/libc.so.6
#1 0x4066cbf0 in ?? () from /usr/lib/libglib-1.2.so.0
#2 0x4066c634 in ?? () from /usr/lib/libglib-1.2.so.0
#3 0x4066c979 in ?? () from /usr/lib/libglib-1.2.so.0
#4 0x4059bf3a in ?? () from /usr/lib/libgtk-1.2.so.0
#5 0x40222a19 in ?? () from /builds/seth/MOZILLA/06.23.1999/04.30/mozilla/dist/bin/libwidgetgtk.so
#6 0x4015617d in ?? () from /builds/seth/MOZILLA/06.23.1999/04.30/mozilla/dist/bin/libnsappshell.so
#7 0x804aa00 in main (argc=2, argv=0xbffffa04) at nsAppRunner.cpp:670
#8 0x407cecb3 in ?? () from /lib/libc.so.6
(gdb)
To load the symbol tables, type this at the gdb prompt:
(gdb) shar libwidgetgtk.so
(gdb) shar libnsappshell.so
(gdb) shar libc.so.6
(gdb) shar libglib-1.2.so.0
(gdb) shar libgtk-1.2.so.0
Now, if I do "where" again to see the stack trace, I get this:
(gdb) where
#0 0x4085e7d0 in __poll (fds=0x83171f8, nfds=3, timeout=19) at ../sysdeps/unix/sysv/linux/poll.c:45
#1 0x4066cbf0 in g_main_poll ()
#2 0x4066c634 in g_main_iterate ()
#3 0x4066c979 in g_main_run ()
#4 0x4059bf3a in gtk_main ()
#5 0x40222a19 in nsAppShell::Run (this=0x80c35e0) at nsAppShell.cpp:237
#6 0x4015617d in nsAppShellService::Run (this=0x80b4a80) at nsAppShellService.cpp:428
#7 0x804aa00 in main (argc=2, argv=0xbffffa04) at nsAppRunner.cpp:670
#8 0x407cecb3 in __libc_start_main (main=0x8049abc <main>,
argc=2, argv=0xbffffa04, init=0x804956c <_init>, fini=0x804b738 <_fini>,
rtld_fini=0x4000a350, stack_end=0xbffff9fc) at ../sysdeps/generic/libc-start.c:78
Advanced tricks:
1) you don't have to type the full library name to load it
"shar msg" will load any libraries (used by the process you are debugging)
that match this pattern lib*msg*
(gdb) shar msg
Reading symbols from /builds/seth/MOZILLA/06.23.1999/04.30/mozilla/dist/bin/libmsgbaseutil.so...done.
Reading symbols from /builds/seth/MOZILLA/06.23.1999/04.30/mozilla/dist/bin/components/libmsgimap.so...done.
Reading symbols from /builds/seth/MOZILLA/06.23.1999/04.30/mozilla/dist/bin/components/libmsgnews.so...done.
Reading symbols from /builds/seth/MOZILLA/06.23.1999/04.30/mozilla/dist/bin/components/libmsgcompose.so...done.
Reading symbols from /builds/seth/MOZILLA/06.23.1999/04.30/mozilla/dist/bin/components/libmsgdb.so...done.
2) mozilla/tools/debug/gdb/solib.gdbinit
I added some macros to load symbols from chunks of code that im
interested in - as opposed to the whole damn thing.
For rdf, mailnews, etc, you will need new entries.
thanks to Arun Sharma for this tip.
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ddd/gdb won't let me set a break point. Why not?
You probably can't set a breakpoint because the library where the symbol lives isn't loaded yet.
(This happens if you are using the "auto-solib-add" trick (from #4).)
But here's a trick from blizzard@redhat.com:
"You can't set a breakpoint in a library that hasn't been loaded but you can
set a breakpoint in _dl_open and set the breakpoint once the library has been
loaded. It's not pretty but it works."
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Where do I break to track down aborts?
PR_ASSERT() vs NS_ASSERTION() on Linux.
(gdb) b abort
(gdb) b exit
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What is strace and how do I use it?
strace is your friend. more on this later.
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Why do I keep stopping with SIG32? How do I stop that?
For rh 6.0, you may need to add this line to your $HOME/.gdbinit file:
handle SIG32 nostop
With the landing of Necko, mozilla is a multi-threaded application on Unix.
Unfortunately, this confuses pthreads when run under gdb on glibc 2.1 with the auto-solib-add option.
The solution is to have libpthread.so loaded when the first thread gets
created. One trick to do this is to set a breakpoint in main() and then load libpthread at this point:
gdb ./apprunner
GNU gdb 4.17.0.11 with Linux support
Copyright 1998 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i386-redhat-linux"...
(gdb) tbreak main
Breakpoint 1 at 0x804b289: file nsAppRunner.cpp, line 808.
(gdb) run
Starting program: .../mozilla/dist/bin/./apprunner
Breakpoint 1, main (argc=1, argv=0xbffff8a4) at nsAppRunner.cpp:808
808 rv = NS_InitXPCOM(NULL);
(gdb) sha pthread
Reading symbols from /lib/libpthread.so.0...done.
(gdb) cont
You can also add these lines to your .gdbinit:
def prun
tbreak main
run
sha pthread
cont
end
And then simply type "prun" instead of "run" to run apprunner.
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How do I use the
LD_BIND_NOW environment variable?
You might want to add information about environment. I always
have this
set:
export LD_BIND_NOW=1
or, if you are using tcsh as your shell:
setenv LD_BIND_NOW 1
The LD_BIND_NOW=1 keeps the dynamic linker from lazily linking symbols.
This means that when you're walking through code you never suddenly
end up in the dynamic loader hunting for a symbol.
from Christopher Blizzard <blizzard@redhat.com>
- This is too hard, just give me a .gdbinit that works.
.gdbinit
- How do I display PRUnichar's?
Several people have suggested ways to do this:
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(gdb) print ((PRUnichar*)uri.mBuffer)[0]@16
$47 = {114, 100, 102, 58, 110, 117, 108, 108, 0, 0, 8, 0, 0, 0, 37432,
16514}
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Define a small helper function "punichar" in #ifdef NS_DEBUG code somewhere.
- Debian's gdb doesn't work. What do I do?
[submitted by Bruce Mitchener]
Debian's unstable distribution currently uses glibc 2.1 and gdb 4.18.
However, there is no package of gdb for Debian with the appropriate threads
patches that will work with glibc 2.1. I was able to get this to work by
getting the gdb 4.18 RPM from Red Hat's rawhide server and installing that.
It has all of the patches necessary for debugging threaded software. These
fixes are expected to be merged into gdb, which will fix the problem for
Debian Linux.
- "run" or "prun" in gdb with "error in loading
shared libraries."
Attempting to run apprunner inside gdb fails with an error message
similar to the following:
Starting program: /u/dmose/s/mozilla/mozilla-all/mozilla/dist/bin/./apprunner /u/dmose/s/mozilla/mozilla-all/mozilla/dist/bin/./apprunner: error in loading shared libraries: libraptorgfx.so: cannot open shared object file: No such file or directory
Your LD_LIBRARY_PATH is probably being reset by your .cshrc or
.profile. From the gdb manual:
*Warning:* GDB runs your program using the shell indicated by your
`SHELL' environment variable if it exists (or `/bin/sh' if not). If
your `SHELL' variable names a shell that runs an initialization
file--such as `.cshrc' for C-shell, or `.bashrc' for BASH--any
variables you set in that file affect your program. You may wish to
move setting of environment variables to files that are only run when
you sign on, such as `.login' or `.profile'.
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I have questions.
post your questions to this newsgroup:
news://news.mozilla.org/netscape.public.mozilla.unix
If you are trying to debug Mozilla on UNIX, we'll gladly help.
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I have comments.
post your constructive comments to this newsgroup:
news://news.mozilla.org/netscape.public.mozilla.unix
whining will be ignored.
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I want to add to this FAQ. Who I send my additions to?
post your additions to this newsgroup:
news://news.mozilla.org/netscape.public.mozilla.unix or send mail to sspitzer@netscape.com.
