From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pierre Muller <pierre@idefix.wisa.be>
To: "Oldham, Adam" <adam.oldham@marconi.com>, "'Andrew Cagney'" <ac131313@cygnus.com>, Daniel Jacobowitz <drow@mvista.com>
Cc: Maurice Lombardi <Maurice.Lombardi@ujf-grenoble.fr>, gdb@sources.redhat.com, core@freepascal.org, gpc@gnu.de
Subject: Re: GDB scope does not work quite right for Pascal
Date: Fri, 12 Oct 2001 16:38:00 -0000
Message-ID: <3.0.6.32.20011013014346.00b8dd40@idefix.wisa.be>
References: <A3E34B558F5CD211B4980008C7A4A99003883EC6@sparrow.gso.mcs.marconi.com>
X-SW-Source: 2001-10/msg00135.html
Message-ID: <20011012163800.FWgSpIthzne3nKyOUCMfb_tltdhPuUnBNFbShOsWRbE@z>

At 14:18 12/10/01 -0400, Oldham, Adam wrote:
>Yes, I saw some of these threads, but nothing seemed to shed light on fixes
>for the scoping of this.  It is good to know Ada does this as well so that
>maybe us Ada/Pascal people can get together and come up with a fix.
>
>I submitted code that demonstrates this with my bug report as well....

  After some testing on both GNU C and GNU Pascal
I discovered that they both use the same method (on djgpp i386 target)

  The calling frame pointer is passed to the nested function
in %ecx register and stored in -4(%ebp) in the function prologue
(which does not seem to be handled by skip_prologue function,
at least I didn't find anything in version 5.0 sources)

  So the parent frame is placed in %ecx and
stored at offset -4 for GNU gcc or gpc
while it is pushed at offset 8 in Free Pascal code.

  Using -gstabs+ I saw nothing generated to explain the meaning
of the %ecx parameter or the -4(%ebp) location.

  Checking the prologue for this movl %ecx,offset(%ebp)
isn't probably sufficient to tell that we are in a nested proc...
Moreover this is processor specific, which is bad...

  Stabs does give info about nesting in the stabs concerning the
   
Consider the following source:
int
test ()
{
  int i = 1;
  int j;

  int local ()
  {
    return j+1;
  };

  j = i+1;
  return local ();
}

int
main ()
{
  printf(" result of test() is %d \n",test());
  return 0;
}


This generates
.stabs "local:f(0,1),local,test",36,0,8,_local.3
The ,local,test indicates that local is nested inside test function.

  But this is not enough as I don't know what happens for instance
if parameters are passed by registers...

  Adding some debug info concerning the location of the 
parent frame seems like a good idea, no ?
The Free Pascal approach to use a pseudo parameter called
'parent_ebp' seems to not be applicable to C as this would
be a valid C local variable name. Maybe something beginning
with a dollar like for the classes?

  A similar problem exists for With statements in pascal.
Stabs defines even a specific stab number for this but this 
is also unsupported for now.