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

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Prompted by:	X11 & XFree86
This commit is contained in:
Poul-Henning Kamp 1997-06-12 12:45:45 +00:00
parent 281e052e36
commit 7c5232c617
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=26579
2 changed files with 27 additions and 8 deletions
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21
lib/libc/stdlib/malloc.3
View File

@ -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.

14
lib/libc/stdlib/malloc.c
View File

@ -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);
}