Re: Problem with location lists and variables on stack

[Daniel Jacobowitz <drow at mvista dot com>]

On Wed, Oct 01, 2003 at 05:44:15PM +0200, Josef Zlomek wrote:
> > > Let the local variables and (some) arguments be addressed using stack pointer,
> > > for example x86-64 architecture with variables addressed using %rsp.
> > > The address emitted for variables located on stack by my new patch is always
> > > DW_OP_fbreg + constant.
> > > 
> > > When I was testing the emitted debug info with mainline GDB I found that
> > > GDB probably does not adjust addresses of variables when stack pointer changes
> > > (like because of "pushq" instruction) if using location lists.
> > > I think GDB should adjust the address of %rsp addressed variables according to
> > > change of %rsp (probably DWARF2 sais so for DW_OP_fbreg). I think it is a
> > > better solution than emitting new locations to location list for all variables
> > > located on stack after each "push" and "pop" which would cause too large debug
> > > info.
> > > 
> > > When I looked to gdb/dwarf2loc.c I see there:
> > >  /* FIXME: cagney/2003-03-26: This code should be using
> > >      get_frame_base_address(), and then implement a dwarf2 specific
> > >      this_base method.  */
> > > Probably this is related to my problem.
> > 
> > The FIXME is a cleanliness problem.  We do evaluate DW_AT_frame_base,
> > so it _ought_ to work.
> > 
> > > I tested it on attached C file, assembler with debug info and x86-64 binary
> > > is attached too.
> > 
> > Do you suppose you could produce an x86 (ia32) testcase?  I don't have
> > x86-64 hardware available yet.  The debug info looks right so I'd like
> > to get my fingers into the problem.
> 
> Here is the x86 assembler.

Thanks.  I'll get back to you... loading m-i386 into gdb and saying
"list" causes a segfault in dwarf2_read_section, so I have some
groundwork to do.

Blast!  Location list support for paramaters (as opposed to locals) was
added to GDB after 6.0 branched, and I never thought to move it over. 
It's too late now, so it will have to go in 6.0.1.


-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer