1.\" $OpenBSD: malloc.9,v 1.68 2022/02/03 17:18:22 guenther Exp $ 2.\" $NetBSD: malloc.9,v 1.2 1996/10/30 05:29:54 lukem Exp $ 3.\" 4.\" Copyright (c) 1996 The NetBSD Foundation, Inc. 5.\" All rights reserved. 6.\" 7.\" This code is derived from software contributed to The NetBSD Foundation 8.\" by Paul Kranenburg. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE 23.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29.\" POSSIBILITY OF SUCH DAMAGE. 30.\" 31.Dd $Mdocdate: February 3 2022 $ 32.Dt MALLOC 9 33.Os 34.Sh NAME 35.Nm malloc , 36.Nm mallocarray , 37.Nm free 38.Nd kernel memory allocator 39.Sh SYNOPSIS 40.In sys/types.h 41.In sys/malloc.h 42.Ft void * 43.Fn malloc "size_t size" "int type" "int flags" 44.Ft void * 45.Fn mallocarray "size_t nmemb" "size_t size" "int type" "int flags" 46.Ft void 47.Fn free "void *addr" "int type" "size_t size" 48.Sh DESCRIPTION 49The 50.Fn malloc 51function allocates uninitialized memory in kernel address space for an 52object whose size is specified by 53.Fa size . 54.Pp 55The 56.Fn mallocarray 57function is the same as 58.Fn malloc , 59but allocates space for an array of 60.Fa nmemb 61objects and checks for arithmetic overflow. 62.Pp 63The 64.Fn free 65function releases memory at address 66.Fa addr 67that was previously allocated by 68.Fn malloc 69or 70.Fn mallocarray 71for re-use. 72The same object size originally provided to 73.Fn malloc 74should be specified by 75.Fa size , 76because 77.Fn free 78will operate faster knowing this. 79If tracking the size is difficult, specify 80.Ar size 81as 0. 82If 83.Fa addr 84is a null pointer, no action occurs. 85.Pp 86The 87.Fa flags 88argument affects the operational characteristics of 89.Fn malloc 90and 91.Fn mallocarray 92as follows: 93.Bl -tag -width xxx -offset indent 94.It Dv M_WAITOK 95If memory is currently unavailable, 96.Fn malloc 97may call sleep to wait for resources to be released by other processes. 98.It Dv M_NOWAIT 99Causes 100.Fn malloc 101to return 102.Dv NULL 103if the request cannot be immediately fulfilled due to resource shortage. 104.It Dv M_CANFAIL 105In the 106.Dv M_WAITOK 107case, if not enough memory is available, return 108.Dv NULL 109instead of calling 110.Xr panic 9 . 111If 112.Fn mallocarray 113detects an overflow 114or 115.Fn malloc 116detects an excessive allocation, return 117.Dv NULL 118instead of calling 119.Xr panic 9 . 120.It Dv M_ZERO 121Causes allocated memory to be zeroed. 122.El 123.Pp 124One of 125.Dv M_NOWAIT 126or 127.Dv M_WAITOK 128must be specified via the 129.Fa flags 130argument. 131.Pp 132The 133.Fa type 134argument broadly identifies the kernel subsystem for which the allocated 135memory was needed, and is commonly used to maintain statistics about 136kernel memory usage. 137These statistics can be examined using 138.Xr vmstat 8 139or 140.Xr systat 1 141if either of the kernel 142.Xr options 4 143.Cm KMEMSTATS 144or 145.Cm DEBUG 146are enabled. 147.Pp 148The following types are currently defined: 149.Pp 150.Bl -tag -offset indent -width XXXXXXXXXXXXXX -compact 151.It Dv M_FREE 152Should be on free list. 153.It Dv M_DEVBUF 154Device driver memory. 155.It Dv M_PCB 156Protocol control blocks. 157.It Dv M_RTABLE 158Routing tables. 159.It Dv M_IFADDR 160Interface addresses. 161.It Dv M_SYSCTL 162Sysctl persistent buffers. 163.It Dv M_COUNTERS 164Per-CPU Counters for use via 165.Xr counters_alloc 9 . 166.It Dv M_IOCTLOPS 167Ioctl data buffers. 168.It Dv M_IOV 169Large IOVs. 170.It Dv M_MOUNT 171VFS mount structs. 172.It Dv M_NFSREQ 173NFS request headers. 174.It Dv M_NFSMNT 175NFS mount structures. 176.It Dv M_VNODE 177Dynamically allocated vnodes. 178.It Dv M_DQUOT 179UFS quota entries. 180.It Dv M_UFSMNT 181UFS mount structures. 182.It Dv M_SHM 183SVID compatible shared memory segments. 184.It Dv M_VMMAP 185VM map structures. 186.It Dv M_SEM 187SVID compatible semaphores. 188.It Dv M_DIRHASH 189UFS directory hash structures. 190.It Dv M_ACPI 191ACPI structures. 192.It Dv M_VMPMAP 193VM pmap data. 194.It Dv M_FILEDESC 195Open file descriptor tables. 196.It Dv M_SIGIO 197Sigio structures. 198.It Dv M_PROC 199Proc structures. 200.It Dv M_SUBPROC 201Proc sub-structures. 202.It Dv M_MFSNODE 203MFS vnode private part. 204.It Dv M_NETADDR 205Export host address structures. 206.It Dv M_NFSSVC 207NFS server structures. 208.It Dv M_NFSD 209NFS server daemon structures. 210.It Dv M_IPMOPTS 211Internet multicast options. 212.It Dv M_IPMADDR 213Internet multicast addresses. 214.It Dv M_IFMADDR 215Link-level multicast addresses. 216.It Dv M_MRTABLE 217Multicast routing tables. 218.It Dv M_ISOFSMNT 219ISOFS mount structures. 220.It Dv M_ISOFSNODE 221ISOFS vnode private part. 222.It Dv M_MSDOSFSMNT 223MSDOS FS mount structures. 224.It Dv M_MSDOSFSFAT 225MSDOS FS FAT tables. 226.It Dv M_MSDOSFSNODE 227MSDOS FS vnode private part. 228.It Dv M_TTYS 229Allocated tty structures. 230.It Dv M_EXEC 231Argument lists & other mem used by exec. 232.It Dv M_MISCFSMNT 233Miscellaneous FS mount structures. 234.It Dv M_FUSEFS 235FUSE FS mount structures. 236.It Dv M_PFKEY 237Pfkey data. 238.It Dv M_TDB 239Transforms database. 240.It Dv M_XDATA 241IPsec data. 242.It Dv M_PAGEDEP 243File page dependencies. 244.It Dv M_INODEDEP 245Inode dependencies. 246.It Dv M_NEWBLK 247New block allocation. 248.It Dv M_INDIRDEP 249Indirect block dependencies. 250.It Dv M_VMSWAP 251VM swap structures. 252.It Dv M_UVMAMAP 253UVM amap and related. 254.It Dv M_UVMAOBJ 255UVM aobj and related. 256.It Dv M_USB 257USB general. 258.It Dv M_USBDEV 259USB device driver. 260.It Dv M_USBHC 261USB host controller. 262.It Dv M_WITNESS 263.Xr witness 4 264memory. 265.It Dv M_MEMDESC 266Memory range. 267.It Dv M_CRYPTO_DATA 268.Xr crypto 9 269data buffers. 270.It Dv M_CREDENTIALS 271.Xr ipsec 4 272related credentials. 273.It Dv M_IP6OPT 274IPv6 options. 275.It Dv M_IP6NDP 276IPv6 neighbour discovery structures. 277.It Dv M_TEMP 278Miscellaneous temporary data buffers. 279.It Dv M_NTFSMNT 280NTFS mount structures. 281.It Dv M_NTFSNTNODE 282NTFS ntnode information. 283.It Dv M_NTFSFNODE 284NTFS fnode information. 285.It Dv M_NTFSDIR 286NTFS directory buffers. 287.It Dv M_NTFSNTHASH 288NTFS ntnode hash tables. 289.It Dv M_NTFSNTVATTR 290NTFS file attribute information. 291.It Dv M_NTFSRDATA 292NTFS resident data. 293.It Dv M_NTFSDECOMP 294NTFS decompression temporary storage. 295.It Dv M_NTFSRUN 296NTFS vrun storage. 297.It Dv M_KEVENT 298.Xr kqueue 2 299data structures. 300.It Dv M_SYNCACHE 301SYN cache hash array. 302.It Dv M_UDFMOUNT 303UDF mount structures. 304.It Dv M_UDFFENTRY 305UDF file entries. 306.It Dv M_UDFFID 307UDF file ID. 308.It Dv M_AGP 309AGP memory. 310.It Dv M_DRM 311Direct Rendering Manager. 312.El 313.Sh CONTEXT 314.Fn malloc 315and 316.Fn mallocarray 317can be called during autoconf, from process context, or from interrupt context 318if 319.Dv M_NOWAIT 320is passed via 321.Fa flags . 322They can't be called from interrupt context if 323.Dv M_WAITOK 324is passed via 325.Fa flags . 326.Pp 327.Fn free 328can be called during autoconf, from process context, or from interrupt context. 329.Sh RETURN VALUES 330.Fn malloc 331and 332.Fn mallocarray 333return a kernel virtual address that is suitably aligned for storage of 334any type of object. 335.Sh DIAGNOSTICS 336A kernel compiled with the 337.Dv DIAGNOSTIC 338configuration option attempts to detect memory corruption caused by 339such things as writing outside the allocated area and unbalanced calls to 340.Fn malloc 341or 342.Fn mallocarray , 343and 344.Fn free . 345Failing consistency checks will cause a panic or a system console message: 346.Pp 347.Bl -bullet -offset indent -compact 348.It 349panic: 350.Dq malloc: bogus type 351.It 352panic: 353.Dq malloc: out of space in kmem_map 354.It 355panic: 356.Dq malloc: allocation too large 357.It 358panic: 359.Dq malloc: wrong bucket 360.It 361panic: 362.Dq malloc: lost data 363.It 364panic: 365.Dq mallocarray: overflow 366.It 367panic: 368.Dq free: unaligned addr 369.It 370panic: 371.Dq free: duplicated free 372.It 373panic: 374.Dq free: multiple frees 375.It 376panic: 377.Dq free: non-malloced addr 378.It 379panic: 380.Dq free: size too large 381.It 382panic: 383.Dq free: size too small 384.It 385panic: 386.Dq kmeminit: minbucket too small/struct freelist too big 387.It 388.Dq multiply freed item Aq addr 389.It 390.Dq Data modified on freelist: Aq data object description 391.El 392.Sh SEE ALSO 393.Xr systat 1 , 394.Xr vmstat 8 395