Re: Problem with location lists and variables on stack

[Josef Zlomek <zlomj9am at artax dot karlin dot mff dot cuni dot cz>]

> > I writing a better pass (variable tracking) for GCC which finally emits
> > location lists for variables. (If you are insterested it is at
> > http://artax.karlin.mff.cuni.cz/~zlomj9am/download/vt-main.patch
> > It still contains many debugging checks and (disabled) prints.)
> > 
> > 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.

I think it will be the same on i386 with -fomit-frame-pointer.
I'll test it and send you files if needed.

Josef