Re: gdb questions

[Jamie Guinan <guinan at bluebutton dot com>]

On Wed, 18 Jul 2001, Eli Zaretskii wrote:

> > From: "Andrew Zimmerman" <andrew@zimmerman.net>
> > Date: Wed, 18 Jul 2001 13:54:07 -0500
> >
> > 1. If gdb is used with assembly language what kind of debugging symbols are
> > required? I'd like to use NASM, but it doesn't seem to be able to add
> > symbols.
>
> If you use Gas, the GNU assembler, you can invoke it with -gstabs+ or
> -gdwarf-2 switches, and get stabs or DWARF2 debug info.

My Gas [1] only supports: -gstabs, -gdwarf, and -gdwarf2.  gcc accepts
-gstabs+ and -gdwarf-2, but does not appear to pass them down to the
assembler (aside from using -Wa).

But -gstabs (and -gdwarf{,2}) do indeed work with assembly source,

  $ as -gstabs foo.S -o foo.o
  $ gcc foo.o -o foo
  $ gdb foo
  (gdb) list foo_func
  ...

-Jamie

[1] stock Red Hat 7.1, gas 2.10.91.  I just note this because I don't know
if latest CVS Gas is any different.


> > 2. Does gdb have a way to examine the LDT (local descriptor table)? My
> > application creates some additional selectors for segments that reside
> > within the flat memory space allocated to the application.
>
> Do you intend to port that code to Linux?  I don't know much about the
> protection scheme employed by Linux, but from what I know, I'd doubt
> very much that it will allow you to futz with the LDT.
>
> > With the Phar Lap
> > Dos Extender we could easily display a list of the segments. And yes, we
> > were in 32-bit protected mode, way back in 1989.
>
> That's funny: I've just committed a few days ago a bunch of changes to
> the DJGPP port of GDB which introduce commands to display LDT, GDT,
> and other system-related info.  You can now say "info dos ldt $cs" and
> see the LDT entry for the debuggee's CS selector, including base
> address, limit, and the access right bits.
>
> But these command only work in GDB when it is compiled for native
> debugging of DJGPP programs.  DJGPP programs are 32-bit protected-mode
> programs which can run on DOS and all versions of Windows as DPMI
> clients.
>

-- 
================================================================
Jamie Guinan                         Blue Button Solutions, Inc.
guinan@bluebutton.com                 http://www.bluebutton.com/
================================================================