From: Nigel Stephens <nigel AT algor DOT co DOT uk>
Date: Tue, 20 Sep 94 16:06:12 +0100
To: Cuthalion / Sliced Bread <enrico AT max DOT tiac DOT net>
Cc: S_Eckart AT lis DOT e-technik DOT tu-muenchen DOT de, djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Re: strange linker behavior
References: <199409201040 DOT GAA22528 AT max DOT tiac DOT net>

Cuthalion / Sliced Bread (enrico AT max DOT tiac DOT net) writes:
 > SE> int delay;
 > SE> 
 > SE> main()
 > SE> {
 > SE>   printf("%d\n",delay);
 > SE> }
 > SE> 
 > SE> I would have expected to get a 0 as output, and in fact this was the
 > SE> case until v1.11m5. The current version prints a large negative
 > SE> number...
 >    I don't think that there's any provision in the C language for what 
 > uninitialized variables
 > start out as.  delay could end up as anything!  

The C language does specify that all such variables should have the
value zero.  This problem *may* be due to the following bug in GO32,
which I found causes random "DPMI: not enough memory" errors.

In some cases GO32 calculates the wrong starting address for the .bss
segment (due to the linker rounding it up to the next 8 byte
boundary).  This causes the last few bytes of the bss segment remain
uninitialised.  For me the final last variable in .bss is often
_stklen, and if this is non-zero when running under DPMI then the
_setstack() routine (called by the startup code) attempts to allocate
a vast stack, which of course fails and gives the above error.  

It is possible that for other programs other variables will not be
completely zeroed.  Use "nm -n" to see which variables are at the end
of .bss.

The following patches to go32 1.12m1 fix the above problem, together
with the following minor cosmetic changes:

1) Correct the final character of the "topline" info.

2) When "meminfo" is set, display the amount of conventional memory
   available, as well as the extended/vcpi memory.

3) Indicate when GO32 does not have enough conventional memory
   available (as opposed to extended, etc)

 _________________________________________________________________________
 Nigel Stephens, Algorithmics Ltd, 3 Drayton Park, London, N5 1NU, England
 phone: +44 71 700 3301    fax: +44 71 700 3400   email: nigel AT algor DOT co DOT uk


*** 1.3	1994/09/07 17:48:05
--- paging.c	1994/09/20 14:06:54
***************
*** 104,110 ****
          "emu"
  };
  #endif
! static char achar[MAX_AREA] = "tdbmsg?e";
  
  word32 far *pd = 0;
  word8 pd_seg[1024];
--- 104,110 ----
          "emu"
  };
  #endif
! static char achar[MAX_AREA] = "tdbmsg??e";
  
  word32 far *pd = 0;
  word8 pd_seg[1024];
***************
*** 495,503 ****
    if (debug_mode)
      fprintf(stderr, "%ld+", aouthdr.dsize);
  
!   areas[A_bss].first_addr = areas[A_data].last_addr + 1;
    areas[A_bss].foffset = -1;
    areas[A_bss].last_addr = areas[A_bss].first_addr + aouthdr.bsize - 1;
    if (debug_mode)
      fprintf(stderr, "%ld = %ld\n", aouthdr.bsize,
        aouthdr.tsize+aouthdr.dsize+aouthdr.bsize);
--- 495,507 ----
    if (debug_mode)
      fprintf(stderr, "%ld+", aouthdr.dsize);
  
!   if (filehdr.f_magic == 0x14c)
!     areas[A_bss].first_addr = scnhdr[2].s_vaddr + ARENA;
!   else
!     areas[A_bss].first_addr = areas[A_data].last_addr + 1;
    areas[A_bss].foffset = -1;
    areas[A_bss].last_addr = areas[A_bss].first_addr + aouthdr.bsize - 1;
+ 
    if (debug_mode)
      fprintf(stderr, "%ld = %ld\n", aouthdr.bsize,
        aouthdr.tsize+aouthdr.dsize+aouthdr.bsize);
*** 1.3	1994/09/07 17:48:05
--- valloc.c	1994/09/07 17:51:18
***************
*** 186,195 ****
    intr(0x21, &r);       /* lol == size of largest free memory block */
  
    lol = r.r_bx;
  /*  printf("max pages is %u\n", lol); */
    if (lol < 8*256)
    {
!     fprintf(stderr, "Error: not enough memory to run go32!\n");
      exit(1);
    }
  
--- 186,198 ----
    intr(0x21, &r);       /* lol == size of largest free memory block */
  
    lol = r.r_bx;
+   if (show_memory_info)
+     fprintf(stderr, "Conventional memory available: %ld Kb\n",
+ 	    lol * 16L / 1024L);
  /*  printf("max pages is %u\n", lol); */
    if (lol < 8*256)
    {
!     fprintf(stderr, "Error: not enough conventional memory to run go32!\n");
      exit(1);
    }