.\" $OpenBSD: malloc.9,v 1.40 2007/09/07 10:31:10 art Exp $ .\" $NetBSD: malloc.9,v 1.2 1996/10/30 05:29:54 lukem Exp $ .\" .\" Copyright (c) 1996 The NetBSD Foundation, Inc. .\" All rights reserved. .\" .\" This code is derived from software contributed to The NetBSD Foundation .\" by Paul Kranenburg. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the NetBSD .\" Foundation, Inc. and its contributors. .\" 4. Neither the name of The NetBSD Foundation nor the names of its .\" contributors may be used to endorse or promote products derived .\" from this software without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS .\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE .\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS .\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN .\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: September 7 2007 $ .Dt MALLOC 9 .Os .Sh NAME .Nm malloc .Nd kernel memory allocator .Sh SYNOPSIS .Fd #include .Fd #include .Ft void * .Fn malloc "unsigned long size" "int type" "int flags" .Fn MALLOC "space" "cast" "unsigned long size" "int type" "int flags" .Ft void .Fn free "void *addr" "int type" .Fn FREE "void *addr" "int type" .Sh DESCRIPTION The .Fn malloc function allocates uninitialized memory in kernel address space for an object whose size is specified by .Fa size . .Fn free releases memory at address .Fa addr that was previously allocated by .Fn malloc for re-use. The .Fn MALLOC macro variant is functionally equivalent to .Bd -literal -offset indent (space) = (cast)malloc((u_long)(size), type, flags) .Ed .Pp and the .Fn FREE macro variant is equivalent to .Bd -literal -offset indent free((caddr_t)(addr), type) .Ed .Pp These macros should only be used when the .Fa size argument is a constant. .Pp Unlike its standard C library counterpart .Pq Xr malloc 3 , the kernel version takes two more arguments. The .Fa flags argument further qualifies .Fn malloc Ns 's operational characteristics as follows: .Bl -tag -width xxx -offset indent .It Dv M_WAITOK This is defined to be 0, and is therefore most useful as an aid to code readability. In effect, it is the same as having no other .Fa flags specified. If memory is currently unavailable, .Fn malloc may call sleep to wait for resources to be released by other processes. .It Dv M_NOWAIT Causes .Fn malloc to return .Dv NULL if the request cannot be immediately fulfilled due to resource shortage. .It Dv M_CANFAIL In the .Dv M_WAITOK case, if not enough memory is available, return .Dv NULL instead of calling .Xr panic 9 . .Dv M_CANFAIL has no effect if .Dv M_NOWAIT is specified. .It Dv M_ZERO Causes .Fn malloc to return zeroed memory. .El .Pp The .Fa type argument broadly identifies the kernel subsystem for which the allocated memory was needed, and is commonly used to maintain statistics about kernel memory usage. The following types are currently defined: .Pp .Bl -tag -offset indent -width XXXXXXXXXXXXXX -compact .It Dv M_FREE Should be on free list. .It Dv M_MBUF Mbuf memory. .It Dv M_DEVBUF Device driver memory. .It Dv M_DEBUG .Nm malloc debug structures. .It Dv M_PCB Protocol control blocks. .It Dv M_RTABLE Routing tables. .It Dv M_FTABLE Fragment reassembly headers. .It Dv M_IFADDR Interface addresses. .It Dv M_SOOPTS Socket options. .It Dv M_SYSCTL Sysctl persistent buffers. .It Dv M_IOCTLOPS Ioctl data buffers. .It Dv M_IOV Large IOVs. .It Dv M_MOUNT VFS mount structs. .It Dv M_NFSREQ NFS request headers. .It Dv M_NFSMNT NFS mount structures. .It Dv M_NFSNODE NFS vnode private part. .It Dv M_VNODE Dynamically allocated vnodes. .It Dv M_CACHE Dynamically allocated cache entries. .It Dv M_DQUOT UFS quota entries. .It Dv M_UFSMNT UFS mount structures. .It Dv M_SHM SVID compatible shared memory segments. .It Dv M_VMMAP VM map structures. .It Dv M_SEM SVID compatible semaphores. .It Dv M_DIRHASH UFS directory hash structures. .It Dv M_VMPMAP VM pmap data. .It Dv M_FILE Open file structures. .It Dv M_FILEDESC Open file descriptor tables. .It Dv M_PROC Proc structures. .It Dv M_SUBPROC Proc sub-structures. .It Dv M_VCLUSTER Cluster for VFS. .It Dv M_MFSNODE MFS vnode private part. .It Dv M_NETADDR Export host address structures. .It Dv M_NFSSVC NFS server structures. .It Dv M_NFSUID NFS uid mapping structures. .It Dv M_NFSD NFS server daemon structures. .It Dv M_IPMOPTS Internet multicast options. .It Dv M_IPMADDR Internet multicast addresses. .It Dv M_IFMADDR Link-level multicast addresses. .It Dv M_MRTABLE Multicast routing tables. .It Dv M_ISOFSMNT ISOFS mount structures. .It Dv M_ISOFSNODE ISOFS vnode private part. .It Dv M_MSDOSFSMNT MSDOS FS mount structures. .It Dv M_MSDOSFSFAT MSDOS FS FAT tables. .It Dv M_MSDOSFSNODE MSDOS FS vnode private part. .It Dv M_TTYS Allocated tty structures. .It Dv M_EXEC Argument lists & other mem used by exec. .It Dv M_MISCFSMNT Misc. FS mount structures. .It Dv M_PFKEY Pfkey data. .It Dv M_TDB Transforms database. .It Dv M_XDATA IPsec data. .It Dv M_PAGEDEP File page dependencies. .It Dv M_INODEDEP Inode dependencies. .It Dv M_NEWBLK New block allocation. .It Dv M_RAIDFRAME RAIDframe data. .It Dv M_UVMAMAP UVM amap and related. .It Dv M_UVMAOBJ UVM aobj and related. .It Dv M_USB USB general. .It Dv M_USBDEV USB device driver. .It Dv M_USBHC USB host controller. .It Dv M_MEMDESC Memory range. .It Dv M_CRYPTO_DATA .Xr crypto 4 data buffers. .It Dv M_CREDENTIALS .Xr ipsec 4 related credentials. .It Dv M_PACKET_TAGS Packet-attached information tags. .It Dv M_1394CTL IEEE 1394 control structures. .It Dv M_1394DATA IEEE 1394 data buffers. .It Dv M_EMULDATA Per process emulation data. .It Dv M_IP6OPT IPv6 options. .It Dv M_IP6NDP IPv6 neighbour discovery structures. .It Dv M_IP6RR IPv6 router renumbering prefix. .It Dv M_RR_ADDR IPv6 router renumbering interface identifiers. .It Dv M_TEMP Miscellaneous temporary data buffers. .It Dv M_NTFSMNT NTFS mount structures. .It Dv M_NTFSNTNODE NTFS ntnode information. .It Dv M_NTFSNODE NTFS fnode information. .It Dv M_NTFSDIR NTFS directory buffers. .It Dv M_NTFSHASH NTFS ntnode hash tables. .It Dv M_NTFSVATTR NTFS file attribute information. .It Dv M_NTFSRDATA NTFS resident data. .It Dv M_NTFSDECOMP NTFS decompression temporary storage. .It Dv M_NTFSRUN NTFS vrun storage. .It Dv M_KEVENT .Xr kqueue 2 data structures. .It Dv M_BLUETOOTH Bluetooth data structures. .It Dv M_BWMETER Multicast upcall bandwidth meters. .It Dv M_UDFMOUNT UDF mount structures. .It Dv M_UDFFENTRY UDF file entries. .It Dv M_UDFFID UDF file ids. .El .Pp Statistics based on the .Fa type argument are maintained only if the kernel option .Dv KMEMSTATS is used when compiling the kernel .Po the default in current\ \& .Ox kernels .Pc and can be examined by using .Sq vmstat -m . .Sh RETURN VALUES .Fn malloc returns a kernel virtual address that is suitably aligned for storage of any type of object. .Sh DIAGNOSTICS A kernel compiled with the .Dv DIAGNOSTIC configuration option attempts to detect memory corruption caused by such things as writing outside the allocated area and unbalanced calls to the .Fn malloc and .Fn free functions. Failing consistency checks will cause a panic or a system console message: .Bl -bullet -offset indent -compact .Pp .It panic: .Dq malloc - bogus type .It panic: .Dq malloc: out of space in kmem_map .It panic: .Dq malloc: allocation too large .It panic: .Dq malloc: wrong bucket .It panic: .Dq malloc: lost data .It panic: .Dq free: unaligned addr .It panic: .Dq free: duplicated free .It panic: .Dq free: multiple frees .It panic: .Dq kmeminit: minbucket too small/struct freelist too big .It .Dq multiply freed item Aq addr .It .Dq Data modified on freelist: Aq data object description .El .Sh DEBUGGING A kernel compiled with the .Cm MALLOC_DEBUG option allows for more extensive debugging of memory allocations. The .Va debug_malloc_type , .Va debug_malloc_size , .Va debug_malloc_size_lo and .Va debug_malloc_size_hi variables choose which allocation to debug. .Va debug_malloc_type should be set to the memory type and .Va debug_malloc_size should be set to the memory size to debug. 0 can be used as a wildcard. .Va debug_malloc_size_lo and .Va debug_malloc_size_hi can be used to specify a range of sizes if the exact size to debug is not known. When those are used, .Va debug_malloc_size needs to be set to the wildcard. .Dv M_DEBUG can also be specified as an allocation type to force allocation with debugging. .Pp Every call to .Fn malloc with a memory type and size that matches the debugged type and size will allocate two virtual pages. The pointer returned will be aligned so that the requested area will end at the page boundary and the second virtual page will be left unmapped. This way we can catch reads and writes outside the allocated area. .Pp Every call to .Fn free with memory that was returned by the debugging malloc will cause the memory area to become unmapped so that we can catch dangling reads and writes to freed memory. .Pp There are no special diagnostics if any errors are caught by the debugging malloc. The errors will look like normal access to unmapped memory. On a memory access error, the .Ic show malloc command in .Xr ddb 4 can be invoked to see what memory areas are allocated and freed. If the faulting address is within two pages from an address on the allocated list, there was an access outside the allocated area. If the faulting address is within two pages from an address on the free list, there was an access to freed memory. .Pp Care needs to be taken when using the .Cm MALLOC_DEBUG option: the memory consumption can run away pretty quickly and there is a severe performance degradation when allocating and freeing debugged memory types. .Sh SEE ALSO .Xr vmstat 8