Date:	Sun, 24 May 1998 20:27:25 +0300 (IDT)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To:	DJ Delorie <dj AT delorie DOT com>
cc:	djgpp-workers AT delorie DOT com
Subject:	A better stack dump
Message-ID:	<Pine.SUN.3.91.980524202528.12971d-100000@is>
MIME-Version:	1.0

Here's a change that will make it possible to tell if the program bombed 
due to stack overflow (or other stack-related atrocities).  The idea 
belongs to Charles Sandmann; the bugs are, as always, mine alone.

*** src/libc/go32/dpmiexcp.c~2	Sat Mar 14 20:28:34 1998
--- src/libc/go32/dpmiexcp.c	Sat May 23 17:27:06 1998
***************
*** 25,30 ****
--- 25,32 ----
  extern unsigned end __asm__ ("end");
  static unsigned char old_video_mode = 3;
  static int cbrk_vect = 0x1b;		/* May be 0x06 for PC98 */
+ extern unsigned _stklen;
+ extern unsigned __djgpp_stack_limit;
  
  /* These are all defined in exceptn.S and only used here */
  extern int __djgpp_exception_table;
*************** extern int __djgpp_iret, __djgpp_i24;
*** 35,40 ****
--- 37,43 ----
  extern void __djgpp_cbrk_hdlr(void);
  extern int __djgpp_hw_lock_start, __djgpp_hw_lock_end;
  extern __dpmi_paddr __djgpp_old_kbd;
+ extern unsigned djgpp_exception_stack __asm__("exception_stack");
  
  static void
  itox(int v, int len)
*************** show_call_frame(void)
*** 95,106 ****
  {
    unsigned *vbp, *vbp_new, *tos;
    unsigned veip;
!   int max=_farpeekb(_dos_ds, 0x484) + 1;
  
!   if (max < 10 || max > 75)	/* sanity check */
!     max = 10;			/* 10 worked for v2.0 and v2.01 */
    else
!     max -= 14;			/* 12 lines of preamble + 2 for symify */
  
    tos = (unsigned *)__djgpp_selector_limit;
    vbp = (unsigned *)__djgpp_exception_state->__ebp;
--- 98,117 ----
  {
    unsigned *vbp, *vbp_new, *tos;
    unsigned veip;
!   int max;
  
!   if (isatty(STDERR_FILENO))
!   {
!     max =_farpeekb(_dos_ds, 0x484) + 1;	/* number of screen lines */
!     if (max < 10 || max > 75)	/* sanity check */
!       max = 10;			/* 10 worked for v2.0 and v2.01 */
!     else
!       max -= 15;		/* 13 lines of preamble + 2 for symify */
!   }
    else
!     /* This could be MAX_INT.  But the stack can be scrogged, so we
!        limit by the maximum that the stack could hold (2 int's per frame).  */
!     max = _stklen / (2*sizeof(unsigned));
  
    tos = (unsigned *)__djgpp_selector_limit;
    vbp = (unsigned *)__djgpp_exception_state->__ebp;
*************** do_faulting_finish_message(int fake_exce
*** 173,178 ****
--- 184,190 ----
  {
    const char *en;
    unsigned long signum = __djgpp_exception_state->__signum;
+   unsigned excpt_stack_addr = (unsigned)&djgpp_exception_stack;
    int i;
    
    /* check video mode for original here and reset (not if PC98) */
*************** do_faulting_finish_message(int fake_exce
*** 248,253 ****
--- 260,269 ----
    dump_selector("fs", __djgpp_exception_state->__fs);
    dump_selector("gs", __djgpp_exception_state->__gs);
    dump_selector("ss", __djgpp_exception_state->__ss);
+   err("App stack: ["); itox(__djgpp_stack_limit+_stklen, 8);
+   err(".."); itox(__djgpp_stack_limit, 8);
+   err("]  Exceptn stack: ["); itox(excpt_stack_addr+8000, 8);
+   err(".."); itox(excpt_stack_addr, 8); err("]\r\n");
    err("\r\n");
    if (__djgpp_exception_state->__cs == _my_cs())
      show_call_frame();
*************** signal(int sig, SignalHandler func)
*** 273,278 ****
--- 289,296 ----
  }
  
  static const char signames[] = "ABRTFPE ILL SEGVTERMALRMHUP INT KILLPIPEQUITUSR1USR2NOFPTRAP";
+ 
+ void __djgpp_traceback_exit(int);
  
  void __djgpp_traceback_exit(int sig)
  {
*** src/libc/go32/exceptn.S~0	Sun Dec 10 20:36:18 1995
--- src/libc/go32/exceptn.S	Sat May 23 17:27:42 1998
***************
*** 24,30 ****
  /* Length 64 bytes plus non-used FPU */
  	.data
  	.align 4
! 	.lcomm	exception_stack, 8000
  
  	.text
  	.align	4
--- 24,30 ----
  /* Length 64 bytes plus non-used FPU */
  	.data
  	.align 4
! 	.comm	exception_stack, 8000
  
  	.text
  	.align	4
*** src/docs/kb/wc202.~10	Sat May 23 17:34:56 1998
--- src/docs/kb/wc202.txi	Sat May 23 17:53:10 1998
***************
*** 368,370 ****
--- 368,388 ----
  @code{errno} to be zero at the beginning of @code{main}, so it is now
  reset to zero before calling @code{main}.
  @vindex errno
+ 
+ The stack dump printed when a program is aborted or crashes was
+ improved.  First, it is no longer limited to 10 stack frames.  When the
+ standard error stream is connected to the console, the maximum number of
+ frames is computed so that the stack dump will use all the available
+ screen area, without scrolling off the visible part.  For example, at
+ 50-line display, you can have as much as 36 stack frames printed and
+ still see the registers and selectors dump, and the exception mnemonic
+ that preceed it.
+ 
+ When stderr is not the console, the number of printed stack frames is
+ only limited by the stack size of the running program.
+ 
+ In addition, the top and bottom of both the application code stack and
+ the locked stack used for processing exceptions, are printed.  This
+ makes detection of stack overflows and other stack-related atrocities
+ much easier.
+ @cindex stack dump, when aborted or crashed

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