Message-ID: <38655BD4.E9FDBB28@teleline.es>
Date: Sun, 26 Dec 1999 01:05:40 +0100
From: Mariano Alvarez =?iso-8859-1?Q?Fern=E1ndez?= <malfer AT teleline DOT es>
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To: djgpp <djgpp AT delorie DOT com>
Subject: Mini malloc debuger
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Reply-To: djgpp AT delorie DOT com

When I switched from BC++ to DJGPP, the most annoying thing was the lack
of a coreleft routine, because I used it like a mini-malloc debuger.
When I made a new function to my programs, I saved the coreleft value
before and after of using the new function, if they aren't identical I
knew I had a memory hole.

Searching for available malloc debugers for DJGPP, I found they are not
easely usable or you must to modify your code a lot. Because the DJGPP
sources are available I began to try to track the used heap modifying
malloc.c, but it's difficult to understand it. Next, I tried whit the
alternate malloc routine fmalloc.c, it is clear and easy to modify.

I added some global variables to fmalloc.c:

long malloc_info_memory;  // The real heap memory used
long malloc_info_nomem;   // Times malloc return NULL
long malloc_info_nmalloc; // Times malloc was called
long malloc_info_nfree;   // Times free was called
long malloc_info_nfree0;  // Times free was called whith pointer to 0

Now, I use my modified fmalloc.c like a mini-malloc debuger. It's easy
to use, I add the fmalloc.o file to my projects, and I use a simple
routine to show the global variables linked to a hot key. When I'm
satisfied, I delete the fmalloc.o file and comment out the show routine.

Here are the diffs, first let's me correct a bug in fmalloc.c, it don't
check for no memory:

*** src/libc/ansi/stdlib/fmalloc.old Tue Jul 28 15:26:06 1998
--- src/libc/ansi/stdlib/fmalloc.c Wed Oct 20 19:20:36 1999
***************
*** 53,58 ****
--- 53,61 ----

    size = bucket2size[b]+4;
    rv = (char *)sbrk(size);
+   if (rv == (char *)(-1)){
+     return 0;
+     }

    *(int *)rv = b;
    rv += 4;
***************
*** 81,86 ****
--- 84,91 ----
    if (size <= oldsize)
      return ptr;
    newptr = (char *)malloc(size);
+   if( newptr == 0 )
+     return 0;
    memcpy(newptr, ptr, oldsize);
    free(ptr);
    return newptr;

And here my modifications:

*** src/libc/ansi/stdlib/fmalloc.old Wed Oct 20 19:20:36 1999
--- src/libc/ansi/stdlib/fmalloc.c Mon Sep 13 17:23:38 1999
***************
*** 4,9 ****
--- 4,15 ----
  #include <stdlib.h>
  #include <unistd.h>

+ long malloc_info_memory = 0;
+ long malloc_info_nomem = 0;
+ long malloc_info_nmalloc = 0;
+ long malloc_info_nfree = 0;
+ long malloc_info_nfree0 = 0;
+
  char *buckets[32] = {0};
  int bucket2size[32] = {0};

***************
*** 43,64 ****
--- 49,74 ----
    if (bucket2size[0] == 0)
      init_buckets();

+   malloc_info_nmalloc++;
    b = size2bucket(size);
    if (buckets[b])
    {
      rv = buckets[b];
      buckets[b] = *(char **)rv;
+     malloc_info_memory += bucket2size[b];
      return rv;
    }

    size = bucket2size[b]+4;
    rv = (char *)sbrk(size);
    if (rv == (char *)(-1)){
+     malloc_info_nomem++;
      return 0;
      }

    *(int *)rv = b;
    rv += 4;
+   malloc_info_memory += bucket2size[b];
    return rv;
  }

***************
*** 66,74 ****
  free(void *ptr)
  {
    int b;
!   if (ptr == 0)
      return;
    b = *(int *)((char *)ptr-4);
    *(char **)ptr = buckets[b];
    buckets[b] = ptr;
  }
--- 76,88 ----
  free(void *ptr)
  {
    int b;
!   if (ptr == 0){
!     malloc_info_nfree0++;
      return;
+     }
    b = *(int *)((char *)ptr-4);
+   malloc_info_memory -= bucket2size[b];
+   malloc_info_nfree++;
    *(char **)ptr = buckets[b];
    buckets[b] = ptr;
  }

P.D. Sorry for my bad english.