Re: Bizarre GCC problem - how do I debug it?

[David Daney <ddaney at caviumnetworks dot com>]

On 08/06/2010 10:51 AM, Bruce Korb wrote:
> On 08/06/10 10:24, David Daney wrote:
> > On 08/06/2010 10:19 AM, Bruce Korb wrote:
> > > The problem seems to be that GDB thinks all the code belongs to a
> > > single line of text.  At first, it was a file of mine, so I presumed
> > > I had done something strange and passed it off.  I needed to do some
> > > more debugging again and my "-g -O0" output still said all code
> > > belonged to that one line.  So, I made a .i file and compiled that.
> > > Different file, but the same problem.  The .i file contains the
> > > correct preprocessor directives:
> > >
> > >     # 309 "wrapup.c"
> > >     static void
> > >     done_check(void)
> > >     {
> > >
> > > but under gdb:
> > >
> > >     (gdb) b done_check
> > >     Breakpoint 5 at 0x40af44: file /usr/include/gmp.h, line 1661.
> > >
> > > the break point *is* on the entry to "done_check", but the
> > > source code displayed is line 1661 of gmp.h.  Not helpful.
> > > Further, I cannot set break points on line numbers because
> > > all code belongs to the one line in gmp.h.
> > >
> > > Yes, for now I can debug in assembly code, but it isn't very easy.....
> > >
> > > $ gcc --version
> > > gcc (SUSE Linux) 4.5.0 20100604 [gcc-4_5-branch revision 160292]
> > > Copyright (C) 2010 Free Software Foundation, Inc.
> > > This is free software; see the source for copying conditions.  There
> > > is NO
> > > warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
> > > PURPOSE.
> > >
> > > I've googled for:  gcc|gdb wrong source file
> > > which only yields how to examine source files in gdb.
> >
> > Which version of GDB?
> >
> > IIRC with GCC-4.5 you need a very new version of GDB.  This page:
> >
> > http://gcc.gnu.org/gcc-4.5/changes.html
> >
> > indicates that GDB 7.0 or later would be good candidates.
>
> That seems to work.  There are one or two or three bugs then.
> Either gdb needs to recognize an out of sync object code

It cannot do this as it was released before GCC-4.5.

> , or else
> gcc needs to produce object code that forces gdb to object in a way
> more obvious than just deciding upon the wrong file and line --
> or both.  I simply installed the latest openSuSE and got whatever
> was supplied.  It isn't reasonable to expect folks to go traipsing
> through upstream web sites looking for "changes.html" files ....
>
> And, of course, the insight stuff needs to incorporate the latest
> and greatest gdb.  (I don't use ddd because it is _completely_ non-
> intuitive.)

My understanding is that whoever packages GCC and GDB for a particular 
distribution is responsible to make sure that they work together.

In your case it looks like that didn't happen.

David Daney