Re: [LUG] gnu compiler experts anywhere?

[Gordon Henderson <gordon+dcglug@xxxxxxxxxx>]

On Wed, 3 Nov 2010, tom wrote:

> On 03/11/10 08:26, Simon Waters wrote:
> > On 03/11/10 08:05, tom wrote:
> >
> > > When I was a lad....
> > > When one compiles for debug these days the exe file is not the same as
> > > the running version that crashes hence the difficulty of finding certain
> > > problems.

It has an extended symbol table compiled into it with references to source 
code line numbers.

> > > I remember in my youth compiler/linkers making a separate map file that
> > > could be used by the debugger - can the gnu tools do this?

I don't recall the gnu tools ever doing this...

> > Don't know, probably, but you can run add debugging to optimised code -
> > the results are "interesting" at times but works well enough and usually
> > finds problems caused by over optimistic optimisation. Although one
> > wonders what sort of code you are feeding it to find bugs these days....

bugs in the compiler or code we're compiling :)

> > http://www.delorie.com/gnu/docs/gdb/gdb_17.html
> Its not my code and it uses some dynamic build method which makes it really 
> hard to work out whats what!
> And apparently I'm looking for symbol files - gdb can take one but I cant see 
> how to generate one...

Sure it's not a core dump file that you're after?

You may need to enable core-file dumping in the shell - I think most 
distros turn that feature off these days.

e.g.

  gordon @ yakko: cat test.c
  main ()
  {
    int i, j, k ;

    i = 5 ;
    j = 0 ;
    k = i / j ;
  }

  gordon @ yakko: gcc -g test.c
  gordon @ yakko: ./a.out
  Floating exception (core dumped)

  gordon @ yakko: gdb -q a.out core

  warning: Can't read pathname for load map: Input/output error.
  Reading symbols from /lib/i686/cmov/libc.so.6...done.
  Loaded symbols for /lib/i686/cmov/libc.so.6
  Reading symbols from /lib/ld-linux.so.2...done.
  Loaded symbols for /lib/ld-linux.so.2
  Core was generated by `./a.out'.
  Program terminated with signal 8, Arithmetic exception.
  [New process 22138]
  #0  0x080483a1 in main () at test.c:7
  7         k = i / j ;
  (gdb)

Gordon

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