Add yet an option, this time on how to deal with malloc(0) and realloc(ptr.0)

Prompted by:	X11 & XFree86

2 files changed, 27 insertions, 8 deletions

diff --git a/lib/libc/stdlib/malloc.3 b/lib/libc/stdlib/malloc.3
index 9782588..479ab00 100644
--- a/lib/libc/stdlib/malloc.3
+++ b/lib/libc/stdlib/malloc.3
@@ -34,7 +34,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\"     @(#)malloc.3	8.1 (Berkeley) 6/4/93
-.\"     $Id: malloc.3,v 1.9 1997/03/22 23:48:12 mpp Exp $
+.\"     $Id: malloc.3,v 1.10 1997/05/30 20:39:32 phk Exp $
 .\"
 .Dd August 27, 1996
 .Dt MALLOC 3
@@ -149,6 +149,11 @@ This can substantially aid in compacting memory.
 ``utrace'' generate entries for ktrace(1) for all operations.
 Consult the source for this one.
 
+.It V
+``sysV'' operations that attempt to allocate zero bytes will
+return a null pointer.  Be aware of the conflict if you also
+have ``X'' set.
+
 .It X
 ``xmalloc'' 
 rather than return failure,
@@ -217,7 +222,7 @@ Here is a brief description of the error messages and what they mean:
 .Pp
 ``(ES): mumble mumble mumble'':
 malloc have been compiled with -DEXTRA_SANITY and something looks
-fishy in there.  Consult sources and or wizards.
+fishy in there.  Consult sources and/or wizards.
 .Pp
 ``allocation failed''
 if the ``A'' option is specified it is an error for
@@ -272,6 +277,13 @@ would be possible to add a sigblock() around this package,
 but it would have a performance penalty that is not acceptable
 as the default.
 .Pp
+``out of memory''
+The ``X'' flag is active and an allocation of memory failed.
+.Pp
+``open of /dev/zero''
+On certain architectures /dev/zero is used as a source of 
+anonymous pages for the page directory, opening failed.
+.Pp
 ``unknown char in MALLOC_OPTIONS''
 we found something we didn't understand.
 .Sh SEE ALSO
@@ -286,6 +298,9 @@ The
 .Fn malloc
 function conforms to
 .St -ansiC .
+.Sh BUGS
+It can be argued that returning a null pointer when asked to
+allocate zero bytes is a silly response to a silly question.
 .Sh HISTORY
 The present implementation of malloc started out as a filesystem on a drum
 attached to a 20bit binary challenged computer built with discrete germanium
@@ -293,7 +308,7 @@ transistors, and it has since graduated to handle primary storage rather than
 secondary.
 .Pp
 The main difference from other malloc implementations are believed to be that
-the free pages are not accessed until allocated.
+the free pages are not accessed unless allocated.
 Most malloc implementations will store a data structure containing a, 
 possibly double-, linked list in the free chunks of memory, used to tie
 all the free memory together.
diff --git a/lib/libc/stdlib/malloc.c b/lib/libc/stdlib/malloc.c
index 0327517..446f55d 100644
--- a/lib/libc/stdlib/malloc.c
+++ b/lib/libc/stdlib/malloc.c
@@ -6,7 +6,7 @@
  * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
  * ----------------------------------------------------------------------------
  *
- * $Id: malloc.c,v 1.23 1997/05/30 20:39:32 phk Exp $
+ * $Id: malloc.c,v 1.24 1997/06/04 12:55:49 jb Exp $
  *
  */
 
@@ -216,6 +216,9 @@ static int malloc_hint;
 /* xmalloc behaviour ?  */
 static int malloc_xmalloc;
 
+/* sysv behaviour for malloc(0) ?  */
+static int malloc_sysv;
+
 /* zero fill ?  */
 static int malloc_zero;
 
@@ -488,6 +491,8 @@ malloc_init ()
 		case 'J': malloc_junk    = 1; break;
 		case 'u': malloc_utrace  = 0; break;
 		case 'U': malloc_utrace  = 1; break;
+		case 'v': malloc_sysv    = 0; break;
+		case 'V': malloc_sysv    = 1; break;
 		case 'x': malloc_xmalloc = 0; break;
 		case 'X': malloc_xmalloc = 1; break;
 		case 'z': malloc_zero    = 0; break;
@@ -774,7 +779,9 @@ imalloc(size_t size)
     if (suicide)
 	abort();
 
-    if ((size + malloc_pagesize) < size)	/* Check for overflow */
+    if (malloc_sysv && !size)
+	result = 0;
+    else if ((size + malloc_pagesize) < size)	/* Check for overflow */
 	result = 0;
     else if (size <= malloc_maxsize)
 	result =  malloc_bytes(size);
@@ -1179,9 +1186,6 @@ realloc(void *ptr, size_t size)
     }
     if (!ptr) {
 	r = imalloc(size);
-    } else if (ptr && !size) {
-	ifree(ptr);
-	r = 0;
     } else {
         r = irealloc(ptr, size);
     }