Date: Sat, 2 Apr 1994 15:18:33 -0800
From: drupp AT cs DOT washington DOT edu (Douglas Rupp)
To: djgpp AT sun DOT soe DOT clarkson DOT edu, gnat-report AT cs DOT nyu DOT edu
Subject: Problem with generated assembly code
Cc: drupp AT cs DOT washington DOT edu


Below is the debugger output from a program generated by the Gnu C back_end
via the DOS port of the Gnat Ada compiler.  As you can see it blows up at:

000013b4: 0000           add     [eax],al            eax=00000000

I don't know assembly very well, but it appears that something should be
in eax other than all zeroes.  Something went wrong somewhere and I need
help tracking it down.  Below the debugger output is the assembly language 
version of a trivial Ada program which exhibits the error and a C file 
containing the binder output.  It can be compiled and run without the having 
the Ada compiler as follows:

as -o test2.o test2.s   /* the assembly code */
gcc -c b_test2.c        /* the C code from the binder */
gcc -o test2 b_test2.o test2.o

For those of you interested in the Ada aspect, version 1.74 of Gnat was
successfully ported and is available at ftp.cs.washington.edu in file pub/gnat.
The above problem is in version 1.76.  The (almost) identical assembly code,
generated by version 1.76 of Gnat for Sco/Unix,
runs fine on SCO Unix, the differences being the .align clauses all designate
.align 4 vice .align 2.  Conversely, changing the .align clauses to 4 in the 
DOS version have no effect and the program still crashes.

Please help,

Doug Rupp
drupp AT cs DOT washington DOT edu
-----------------------------------------------------------------------------


>> b __ada_test2
  dr0  __ada_test2 (0x13aa)
  dr1  0 (disabled)
  dr2  0 (disabled)
  dr3  _main (0x1360) (disabled)
>> c
eax=00000000  ebx=7ffffc68  ecx=00005010  edx=7ffffc74
esi=00000000  edi=00000000  ebp=7ffffc54              UP IE    PL NZ    PO NC
ds=0048 es=0048 fs=0048 gs=0038 ss:esp=0048:7ffffc50 cs=00d8
breakpoint 0 hit
__ada_test2():
000013aa: 55             push    ebp                 ebp=7ffffc54
>> s
000013ab: 89e5           mov     ebp,esp             esp=7ffffc4c
000013ad: 83c4fe         add     esp,-2              esp=7ffffc4c
000013b0: 6668ff00       push    255
000013b4: 0000           add     [eax],al            eax=00000000
eax=00000000  ebx=7ffffc68  ecx=00005010  edx=7ffffc74
esi=00000000  edi=00000000  ebp=7ffffc4c     RF       UP IE TF PL NZ AC PO CY
ds=0048 es=0048 fs=0048 gs=0038 ss:esp=0048:7ffffc48 cs=00d8
exception 14 (0xe) occurred, error code=0
000013b4: 0000           add     [eax],al            eax=00000000

-----------------------------------------------------------------------------
test2.s
-----------------------------------------------------------------------------

	.file	"test2.ada"
gcc2_compiled.:
___gnu_compiled_ada:
.text
	.align 2
.globl _test2___elabb
_test2___elabb:
	pushl %ebp
	movl %esp,%ebp
L1:
	leave
	ret
	.align 2
.globl _test2___elabs
_test2___elabs:
	pushl %ebp
	movl %esp,%ebp
L2:
	leave
	ret
	.align 2
_set_char_literal_value.0:
	pushl %ebp
	movl %esp,%ebp
	subl $4,%esp
	movl %ecx,-4(%ebp)
	jmp L4
	.align 2,0x90
L4:
	leave
	ret
	.align 2
.globl __ada_test2
__ada_test2:
	pushl %ebp
	movl %esp,%ebp
	addl $-2,%esp
	pushw $255
	movl %ebp,%ecx
	call _set_char_literal_value.0
	addl $4,%esp
	jmp L3
	.align 2,0x90
L3:
	leave
	ret
.comm ___gnat_jmpbuf,4
.comm ___gnat_exception,4

-----------------------------------------------------------------------------
b_test2.c
-----------------------------------------------------------------------------


#include <string.h>
  
/* predefined exceptions */
char constraint_error;
char numeric_error;
char program_error;
char storage_error;
char tasking_error;
 
static int static_argc;
static char * *static_argv;
 
int arg_count () { return static_argc; }
 
int len_arg (arg_num)
   int arg_num;
   { return strlen(static_argv[arg_num]); }
 
int fill_arg (a, i)
   char * a;
   int i;
{ strncpy (a, static_argv[i],
     strlen(static_argv[i])); }
 
void catch_except (ptr, i)
     void *ptr;
     int i;
{
  extern char *__gnat_exception;
 
  if (!ptr)
    {
      if (__gnat_exception == &constraint_error)
        puts ("\nraised Constraint_Error\n");
      else if (__gnat_exception == &numeric_error)
        puts ("\nraised Numeric_Error\n");
      else if (__gnat_exception == &program_error)
        puts ("\nraised Program_Error\n");
      else if (__gnat_exception == &storage_error)
        puts ("\nraised Storage_Error\n");
      else
        puts ("\nraised unhandled exception\n");
 
      exit (1);
   }
  else
    longjmp (ptr, i);
}
 
void __gnat_raise_constraint ()
{
  extern char *__gnat_exception;
  extern void *__gnat_jmpbuf;
  __gnat_exception = &constraint_error;
 
  catch_except (__gnat_jmpbuf, 1);
}
 
void main (argc, argv)
   int argc;
   char * argv[];
{
   static_argc = argc;
   static_argv = argv;
 
   test2___elabb ();			  /* test2.ali */
 
   _ada_test2 ();
   exit (0);
}
/* BEGIN Object file list
test2.o
   END Object file list */