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Date: Thu, 14 Jan 88 08:33:06 PST
Message-Id: <8801141633.AA21398@decwrl.dec.com>
From: reuter%cookie.DEC@decwrl.dec.com (Chocolate helps prevent cavities!)
To: pardo@june.cs.washington.edu
Subject: decomp fixes

Goodness.  Believe it or not, I never tried decompiling a linked
C program.  I only worked with object modules.

The problem is that the decompiler does not recognize the "exit" system
call as a basic block terminator.  This would have been just fine if
the exception handling cases had been written correctly, but they
weren't.  Here are the fixes to the exception code, supplied as
"diff -c" output for the modules "blocks.c" and "nodes.c".

	Jim

*** blocks.c.old	Wed Jan 13 12:40:46 1988
--- blocks.c	Wed Jan 13 12:43:37 1988
***************
*** 14,19
  #include "objfile.h"
  #include "vartab.h"
  #include "nodes.h"
  
  static int op_argval[6];
  
 
--- 14,20 -----
  #include "objfile.h"
  #include "vartab.h"
  #include "nodes.h"
+ #include <setjmp.h>
  
+ extern jmp_buf badbranch;
+ 
  static int op_argval[6];
  
***************
*** 294,300
  	}
      }
      /* no more code in function */
!     if ( cur_address > node_entry )
  	fprintf( stderr, "Dangling function end\n" );
  }
  
 
--- 297,303 -----
  	}
      }
      /* no more code in function */
!     if ( cur_address > node_entry ) {
  	fprintf( stderr, "Dangling function end\n" );
+  	longjmp( badbranch, 1 );
+     }
  }



*** nodes.c.old	Wed Jan 13 12:41:03 1988
--- nodes.c	Wed Jan 13 12:35:59 1988
***************
*** 79,84
      register struct node *n;
      register int i, j;
  
      node_max = node_count * 4;
      node_array = (struct node **) malloc( node_max * sizeof( struct node * ) );
      if ( node_array == NULL ) {
 
--- 79,89 -----
      register struct node *n;
      register int i, j;
  
+     if ( node_count <= 0 ) {
+ 	fprintf( stderr, "Bad node_count in array_nodes()\n" );
+ 	longjmp( badbranch, 1 );
+     }
+ 
      node_max = node_count * 4;
      node_array = (struct node **) malloc( node_max * sizeof( struct node * ) );
      if ( node_array == NULL ) {




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From: ucsd!felix!art@beaver (Art Dederick)
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To: spsd!ucsd!uw-beaver!june.cs.washington.edu!pardo@beaver
Subject: Re: decomp, #2
Date: Sat, 30 Sep 89 07:26:41 PDT

Second try on this message, not sure you got the first attempt.
Send me an ACK if you get either message.  Thanks.

Found the segmentation bug.  I was very stupid and didn't save the
original code so I can't make diffs, sorry about that.  The fix was
easy, just add the following code to the beginning of free_nodes():

    if (node_count && node_array == NULL) {
	fprintf(stderr, "free_nodes: node_count > 0 && node_array == NULL\n");
        return;
    }

I don't know why the node count would be non-zero but the node array
by empty.  You could probably explain it (hint hint :-).

In addition, I added code to remove .o file usage from an a.out file.
I kept getting function names like foo.o() instead of main().  Add the
following code to decomp():

    for (i = 0; i < nsym / sizeof(struct nlist); i++) {
	if ( ((symtab+i)->n_type & ~1) == 4 ) {
|	    char *p, *rindex();
|
|	    p = rindex(&strtab[(symtab+i)->n_un.n_strx], 'o');
|	    if (!p || p[-1] != '.')
		glb_add( (symtab+i)->n_value, i, 1 - ((symtab+i)->n_type & 1) );
	}
    }

This code will skip all entries in the symbol table that have a ".o"
suffix.

Another area I am currently trying to improve is function calling
labels when decompiling a.out files.  Currently only when a .o file is
decompiled will references to functions use the name of the function.
What I am attempting to do is search for the functions address in the
symbol table when a call is made and use the name instead of the
'Gnnnn' label.  So far I'm stumped.

	   __              __
	  /  )    _/_     /  )      /             /
	 /--/ __  /      /  / _  __/ _  __  o _. /_ 
	/  (_/ (_<__    /__/_</_(_/_</_/ (_<_(__/ <_

	felix!art	(714)966-3618
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