1 files changed, 352 insertions, 24 deletions

diff --git a/src/lib/libc/stdlib/malloc.3 b/src/lib/libc/stdlib/malloc.3
index 3bbf2bf65e..8f05c38e86 100644
--- a/src/lib/libc/stdlib/malloc.3
+++ b/src/lib/libc/stdlib/malloc.3
@@ -1,5 +1,6 @@
-.\" Copyright (c) 1980, 1991 Regents of the University of California.
-.\" All rights reserved.
+.\"
+.\" Copyright (c) 1980, 1991, 1993
+.\"     The Regents of the University of California.  All rights reserved.
 .\"
 .\" This code is derived from software contributed to Berkeley by
 .\" the American National Standards Committee X3, on Information
@@ -33,19 +34,32 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"     from: @(#)malloc.3      6.7 (Berkeley) 6/29/91
-.\"     $Id: malloc.3,v 1.1.1.1 1995/10/18 08:42:18 deraadt Exp $
+.\"     $OpenBSD: malloc.3,v 1.24 2001/12/05 09:49:39 deraadt Exp $
 .\"
-.Dd June 29, 1991
+.Dd August 27, 1996
 .Dt MALLOC 3
-.Os BSD 4
+.Os
 .Sh NAME
-.Nm malloc
-.Nd general memory allocation function
+.Nm malloc ,
+.Nm calloc ,
+.Nm realloc ,
+.Nm free ,
+.Nm cfree
+.Nd memory allocation and deallocation
 .Sh SYNOPSIS
 .Fd #include <stdlib.h>
 .Ft void *
 .Fn malloc "size_t size"
+.Ft void *
+.Fn calloc "size_t nmemb" "size_t size"
+.Ft void *
+.Fn realloc "void *ptr" "size_t size"
+.Ft void
+.Fn free "void *ptr"
+.Ft void
+.Fn cfree "void *ptr"
+.Ft char *
+.Va malloc_options
 .Sh DESCRIPTION
 The
 .Fn malloc
@@ -59,33 +73,347 @@ space from the appropriate list.
 .Pp
 The allocated space is
 suitably aligned (after possible pointer
-coercion) for storage of any type of object. If the space is of
+coercion) for storage of any type of object.
+If the space is of
 .Em pagesize
 or larger, the memory returned will be page-aligned.
+.Pp
+Allocation of a zero size object returns a pointer to a zero size object.
+This zero size object is access protected, so any access to it will
+generate an exception (SIGSEGV).
+Many zero-sized objects can be placed consecutively in shared
+protected pages.
+The minimum size of the protection on each object is suitably aligned and
+sized as previously stated, but the protection may extend further depending
+on where in a protected zone the object lands.
+.Pp
+The
+.Fn calloc
+function allocates space for an array of
+.Fa nmemb
+objects, each of whose size is
+.Fa size .
+The space is initialized to all bits zero.
+.Pp
+The
+.Fn free
+function causes the space pointed to by
+.Fa ptr
+to be deallocated, that is, at least made available for further allocation,
+but if possible, it will passed back to the kernel with
+.Xr sbrk 2 .
+If
+.Fa ptr
+is a null pointer, no action occurs.
+.Pp
+A
+.Fn cfree
+function is also provided for compatibility with old systems and other
+.Nm malloc
+libraries; it is simply an alias for
+.Fn free .
+.Pp
+The
+.Fn realloc
+function changes the size of the object pointed to by
+.Fa ptr
+to
+.Fa size
+bytes and returns a pointer to the (possibly moved) object.
+The contents of the object are unchanged up to the lesser
+of the new and old sizes.
+If the new size is larger, the value of the newly allocated portion
+of the object is indeterminate and uninitialized.
+If
+.Fa ptr
+is a null pointer, the
+.Fn realloc
+function behaves like the
+.Fn malloc
+function for the specified size.
+If the space cannot be allocated, the object
+pointed to by
+.Fa ptr
+is unchanged.
+If
+.Fa size
+is zero and
+.Fa ptr
+is not a null pointer, the object it points to is freed and a new zero size
+object is returned.
+.Pp
+When using
+.Fn realloc
+one must be careful to avoid the following idiom:
+.Pp
+.Bd -literal -offset indent
+if ((p = realloc(p, nsize)) == NULL)
+        return NULL;
+.Ed
+.Pp
+In most cases, this will result in a leak of memory.
+As stated earlier, a return value of
+.Dv NULL
+indicates that the old object still remains allocated.
+Better code looks like this:
+.Bd -literal -offset indent
+if ((p2 = realloc(p, nsize)) == NULL) {
+        if (p)
+                free(p);
+        p = NULL;
+        return NULL;
+}
+p = p2;
+.Ed
+.Pp
+Malloc will first look for a symbolic link called
+.Pa /etc/malloc.conf
+and next check the environment for a variable called
+.Ev MALLOC_OPTIONS
+and finally for the global variable
+.Va malloc_options
+and scan them for flags in that order.
+Flags are single letters, uppercase means on, lowercase means off.
+.Bl -tag -width indent
+.It Cm A
+.Dq Abort .
+.Fn malloc
+will coredump the process, rather than tolerate failure.
+This is a very handy debugging aid, since the core file will represent the
+time of failure, rather than when the null pointer was accessed.
+.Pp
+.It Cm D
+.Dq Dump .
+.Fn malloc
+will dump statistics in a file called
+.Pa malloc.out
+at exit.
+This option requires the library to have been compiled with -DMALLOC_STATS in
+order to have any effect.
+.Pp
+.It Cm J
+.Dq Junk .
+Fill some junk into the area allocated.
+Currently junk is bytes of 0xd0; this is pronounced
+.Dq Duh .
+\&:-)
+.Pp
+.It Cm H
+.Dq Hint .
+Pass a hint to the kernel about pages we don't use.
+If the machine is paging a lot this may help a bit.
+.Pp
+.It Cm N
+Do not output warning messages when encountering possible corruption
+or bad pointers.
+.Pp
+.It Cm R
+.Dq realloc .
+Always reallocate when
+.Fn realloc
+is called, even if the initial allocation was big enough.
+This can substantially aid in compacting memory.
+.\".Pp
+.\".It Cm U
+.\".Dq utrace .
+.\"Generate entries for
+.\".Xr ktrace 1
+.\"for all operations.
+.\"Consult the source for this one.
+.Pp
+.It Cm X
+.Dq xmalloc .
+rather than return failure,
+.Xr abort 3
+the program with a diagnostic message on stderr.
+It is the intention that this option be set at compile time by
+including in the source:
+.Bd -literal -offset indent
+extern char *malloc_options;
+malloc_options = "X";
+.Ed
+.Pp
+.It Cm Z
+.Dq Zero .
+Fill some junk into the area allocated (see
+.Cm J ) ,
+except for the exact length the user asked for, which is zeroed.
+.Pp
+.It Cm <
+.Dq Half the cache size .
+Reduce the size of the cache by a factor of two.
+.Pp
+.It Cm >
+.Dq Double the cache size .
+Double the size of the cache by a factor of two.
+.El
+.Pp
+So to set a systemwide reduction of cache size and coredumps on problems
+one would:
+.Li ln -s 'A<' /etc/malloc.conf
+.Pp
+The
+.Cm J
+and
+.Cm Z
+is mostly for testing and debugging.
+If a program changes behavior if either of these options are used,
+it is buggy.
+.Pp
+The default cache size is 16 pages.
+.Sh ENVIRONMENT
+See above.
 .Sh RETURN VALUES
 The
 .Fn malloc
-function returns
-a pointer to the allocated space if successful; otherwise
-a null pointer is returned.
+and
+.Fn calloc
+functions return a pointer to the allocated space if successful; otherwise,
+a null pointer is returned and
+.Va errno
+is set to
+.Er ENOMEM .
+.Pp
+The
+.Fn free
+and
+.Fn cfree
+functions return no value.
+.Pp
+The
+.Fn realloc
+function returns a pointer to the (possibly moved) allocated space
+if successful; otherwise, a null pointer is returned and
+.Va errno
+is set to
+.Er ENOMEM .
+.Sh DIAGNOSTICS
+If
+.Fn malloc ,
+.Fn calloc ,
+.Fn realloc ,
+or
+.Fn free
+detect an error or warning condition,
+a message will be printed to file descriptor
+2 (not using stdio).
+Errors will always result in the process being
+.Xr abort 3 'ed.
+If the
+.Cm A
+option has been specified, warnings will also
+.Xr abort 3
+the process.
+.Pp
+Here is a brief description of the error messages and what they mean:
+.Bl -tag -width Fl
+.It Dq (ES): mumble mumble mumble
+.Fn malloc
+has been compiled with
+.Dv \&-DEXTRA_SANITY
+and something looks fishy in there.
+Consult sources and/or wizards.
+.It Dq allocation failed
+If the
+.Cm A
+option is specified it is an error for
+.Fn malloc ,
+.Fn calloc ,
+or
+.Fn realloc
+to return
+.Dv NULL .
+.It Dq mmap(2) failed, check limits.
+This is a rather weird condition that is most likely to indicate a
+seriously overloaded system or a
+.Xr ulimit 1
+restriction.
+.It Dq freelist is destroyed.
+.Fn malloc Ns 's
+internal freelist has been stomped on.
+.El
+.Pp
+Here is a brief description of the warning messages and what they mean:
+.Bl -tag -width Fl
+.It Dq chunk/page is already free.
+A pointer to a free chunk is attempted freed again.
+.It Dq junk pointer, too high to make sense.
+The pointer doesn't make sense.
+It's above the area of memory that
+.Fn malloc
+knows something about.
+This could be a pointer from some
+.Xr mmap 2 'ed
+memory.
+.It Dq junk pointer, too low to make sense.
+The pointer doesn't make sense.
+It's below the area of memory that
+.Fn malloc
+knows something about.
+This pointer probably came from your data or bss segments.
+.It Dq malloc() has never been called.
+Nothing has ever been allocated, yet something is being freed or
+realloc'ed.
+.It Dq modified (chunk-/page-) pointer.
+The pointer passed to free or realloc has been modified.
+.It Dq pointer to wrong page.
+The pointer that
+.Fn malloc
+is trying to free is not pointing to
+a sensible page.
+.It Dq recursive call.
+An attempt was made to call recursively into these functions, i.e., from a
+signal handler.
+This behavior is not supported.
+In particular, signal handlers should
+.Em not
+use any of the
+.Fn malloc
+functions nor utilize any other functions which may call
+.Fn malloc
+(e.g.,
+.Xr stdio 3
+routines).
+.It Dq unknown char in MALLOC_OPTIONS
+We found something we didn't understand.
+.El
+.Sh FILES
+.Bl -tag -width "/etc/malloc.conf"
+.It Pa /etc/malloc.conf
+symbolic link to filename containing option flags
+.El
 .Sh SEE ALSO
 .Xr brk 2 ,
-.Xr getpagesize 2 ,
-.Xr free 3 ,
-.Xr calloc 3 ,
 .Xr alloca 3 ,
-.Xr realloc 3 ,
+.Xr getpagesize 3 ,
 .Xr memory 3
+.Pa /usr/share/doc/papers/malloc.ascii.gz
 .Sh STANDARDS
 The
 .Fn malloc
 function conforms to
 .St -ansiC .
-.Sh BUGS
-The current implementation of
-.Xr malloc
-does not always fail gracefully when system
-memory limits are approached.
-It may fail to allocate memory when larger free blocks could be broken
-up, or when limits are exceeded because the size is rounded up.
-It is optimized for sizes that are powers of two.
+.Sh HISTORY
+The present implementation of
+.Fn malloc
+started out as a filesystem on a drum
+attached to a 20-bit binary challenged computer built with discrete germanium
+transistors, and it has since graduated to handle primary storage rather than
+secondary.
+.Pp
+The main difference from other
+.Fn malloc
+implementations are believed to be that
+the free pages are not accessed until allocated.
+Most
+.Fn 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.
+That is a quite suboptimal thing to do.
+Every time the free-list is traversed, all the otherwise unused, and very
+likely paged out, pages get faulted into primary memory, just to see what
+lies after them in the list.
+.Pp
+On systems which are paging, this can make a factor five in difference on the
+page-faults of a process.