Re: gdb runs multi-threaded with non-threaded app and gets SEGV

["Min Xu (Hsu)" <xu@cs.wisc.edu>]

Larry,

How about you run the program and let the program pass the
lib call without using GDB. And spin there until gdb is attached?

-Min

On Fri, 15 Jul 2005 Larry Martell wrote :
> --- Ramana Radhakrishnan
> <ramana.radhakrishnan@codito.com> wrote:
> > On Fri, 2005-07-15 at 11:25 -0700, Larry Martell
> > wrote:
> > > I have a program that has 1 line of code - a call
> > to
> > > a third party libary function:
> > >
> > > #include "ni488.h"
> > >
> > > int main() {
> > >         int handle = ibdev(0, 7, 0, 10, 1, 0);
> > > }
> > 
> > 
> > That is not enough info for us to help you with .
> > Try CVS head or a more
> > recent version of gdb and see if that works.
> 
> OK, I've upgraded to gdb 6.3
> 
> > Whats the version of libc ,
> 
> 2.3.3
> 
> > gcc 
> 
> 3.4.1
> 
> > Also maybe your 3rd party
> > library might be multithreaded for all we know. Do a
> > ldd on the library if its a .so and check .
> 
> OK, an ldd showed:
> 
> libpthread.so.0 => /lib/tls/libpthread.so.0
> (0x40278000)
> 
> So apparently the 3rd party lib is multithreaded.
> 
> So that answers 1 question. But the more important one
> is why I get the SEGV in gdb, but not when I run the
> program without gdb?
> 
> Here's the deal - I am developing an app (that is
> not getting a SEGV) and I wanted to debug it. When
> I ran the app in gdb it got the SEGV on my call to
> ibdev. Thinking I probably had a memory corruption
> somewhere in my application I ran valgrind on it.
> It said the 3rd party lib was attempting to jump
> to address 0. Still thinking it was my issue, I
> created the single line test program (shown at the
> top of this message). And that's where I am now - I
> need gdb to get past this call so I can debug my
> actaul app.
> 
> Thanks!
> -larry
> 
> 
> > > The program is not multi-threaded nor does not
> > link
> > > with any multi-threaded libs. It's built like
> > this:
> > >
> > > gcc -g -o nitest nitest.c -lgpibapi
> > >
> > > If I run the program outside of the debugger it
> > does
> > > not crash.
> > >
> > > If I run it from within gdb here's what I get:
> > >
> > > $ gdb nitest
> > > GNU gdb 6.2-2mdk (Mandrakelinux)
> > > Copyright 2004 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
> > > "i586-mandrake-linux-gnu"...Using host
> > libthread_db
> > > library "/lib/tls/libthread_db.so.1".
> > >
> > > (gdb) start
> > > Breakpoint 1 at 0x8048398: file nitest.c, line 4.
> > > Starting program: /home/martell/src/nitest2/nitest
> > > [Thread debugging using libthread_db enabled]
> > > [New Thread 1076484320 (LWP 9873)]
> > > [Switching to Thread 1076484320 (LWP 9873)]
> > > main () at nitest.c:4
> > > 4               int handle = ibdev(0, 7, 0, 10, 1,
> > 0);
> > > (gdb) c
> > > Continuing.
> > > [New Thread 1085078448 (LWP 9876)]
> > > [New Thread 1093471152 (LWP 9877)]
> > >
> > > Program received signal SIGSEGV, Segmentation
> > fault.
> > > [Switching to Thread 1085078448 (LWP 9876)]
> > > 0x4005d609 in ?? () from
> > > /usr/local/lib/libgpibapi.so.2
> > >
> > > Can anyone tell me why gdb runs this as
> > multi-threaded
> > > and why I get a SEGV in gdb, but I do not when I
> > run
> > > it outside of gdb?
> > >
> > > Thanks!
> > > -larry
> > 
> > 
> > 
>