1.\" $OpenBSD: malloc.9,v 1.70 2023/07/03 06:45:44 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: July 3 2023 $ 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.\" START DEFINES sys/malloc.h (M_FREE,M_LAST) 152.It Dv M_DEVBUF 153Device driver memory. 154.It Dv M_PCB 155Protocol control blocks. 156.It Dv M_RTABLE 157Routing tables. 158.It Dv M_PF 159Packet filter structures. 160.It Dv M_IFADDR 161Interface addresses. 162.It Dv M_IFGROUP 163Interface groups. 164.It Dv M_SYSCTL 165Sysctl persistent buffers. 166.It Dv M_COUNTERS 167Per-CPU counters via 168.Xr counters_alloc 9 . 169.It Dv M_IOCTLOPS 170Ioctl data buffers. 171.It Dv M_IOV 172Large IOVs. 173.It Dv M_MOUNT 174VFS mount structs. 175.It Dv M_NFSREQ 176NFS request headers. 177.It Dv M_NFSMNT 178NFS mount structures. 179.It Dv M_LOG 180Messages in kernel log stash. 181.It Dv M_VNODE 182Dynamically allocated vnodes. 183.It Dv M_DQUOT 184UFS quota entries. 185.It Dv M_UFSMNT 186UFS mount structures. 187.It Dv M_SHM 188SVID compatible shared memory segments. 189.It Dv M_VMMAP 190VM map structures. 191.It Dv M_SEM 192SVID compatible semaphores. 193.It Dv M_DIRHASH 194UFS directory hash structures. 195.It Dv M_ACPI 196ACPI structures. 197.It Dv M_VMPMAP 198VM pmap data. 199.It Dv M_FILEDESC 200Open file descriptor tables. 201.It Dv M_SIGIO 202Sigio structures. 203.It Dv M_PROC 204Proc structures. 205.It Dv M_SUBPROC 206Proc sub-structures. 207.It Dv M_MFSNODE 208MFS vnode private part. 209.It Dv M_NETADDR 210Export host address structures. 211.It Dv M_NFSSVC 212NFS server structures. 213.It Dv M_NFSD 214NFS server daemon structures. 215.It Dv M_IPMOPTS 216Internet multicast options. 217.It Dv M_IPMADDR 218Internet multicast addresses. 219.It Dv M_IFMADDR 220Link-level multicast addresses. 221.It Dv M_MRTABLE 222Multicast routing tables. 223.It Dv M_ISOFSMNT 224ISOFS mount structures. 225.It Dv M_ISOFSNODE 226ISOFS vnode private part. 227.It Dv M_MSDOSFSMNT 228MSDOS FS mount structures. 229.It Dv M_MSDOSFSFAT 230MSDOS FS FAT tables. 231.It Dv M_MSDOSFSNODE 232MSDOS FS vnode private part. 233.It Dv M_TTYS 234Allocated tty structures. 235.It Dv M_EXEC 236Argument lists & other mem used by exec. 237.It Dv M_MISCFSMNT 238Miscellaneous FS mount structures. 239.It Dv M_FUSEFS 240FUSE FS mount structures. 241.It Dv M_PFKEY 242Pfkey data. 243.It Dv M_TDB 244Transforms database. 245.It Dv M_XDATA 246IPsec data. 247.It Dv M_PAGEDEP 248File page dependencies. 249.It Dv M_INODEDEP 250Inode dependencies. 251.It Dv M_NEWBLK 252New block allocation. 253.It Dv M_INDIRDEP 254Indirect block dependencies. 255.It Dv M_VMSWAP 256VM swap structures. 257.It Dv M_UVMAMAP 258UVM amap and related. 259.It Dv M_UVMAOBJ 260UVM aobj and related. 261.It Dv M_USB 262USB general. 263.It Dv M_USBDEV 264USB device driver. 265.It Dv M_USBHC 266USB host controller. 267.It Dv M_WITNESS 268.Xr witness 4 269memory. 270.It Dv M_MEMDESC 271Memory range. 272.It Dv M_CRYPTO_DATA 273.Xr crypto 9 274data buffers. 275.It Dv M_CREDENTIALS 276.Xr ipsec 4 277related credentials. 278.It Dv M_IP6OPT 279IPv6 options. 280.It Dv M_IP6NDP 281IPv6 Neighbor Discovery structures. 282.It Dv M_TEMP 283Miscellaneous temporary data buffers. 284.It Dv M_NTFSMNT 285NTFS mount structures. 286.It Dv M_NTFSNTNODE 287NTFS ntnode information. 288.It Dv M_NTFSFNODE 289NTFS fnode information. 290.It Dv M_NTFSDIR 291NTFS directory buffers. 292.It Dv M_NTFSNTHASH 293NTFS ntnode hash tables. 294.It Dv M_NTFSNTVATTR 295NTFS file attribute information. 296.It Dv M_NTFSRDATA 297NTFS resident data. 298.It Dv M_NTFSDECOMP 299NTFS decompression temporary storage. 300.It Dv M_NTFSRUN 301NTFS vrun storage. 302.It Dv M_KEVENT 303.Xr kqueue 2 304data structures. 305.It Dv M_SYNCACHE 306SYN cache hash array. 307.It Dv M_UDFMOUNT 308UDF mount structures. 309.It Dv M_UDFFENTRY 310UDF file entries. 311.It Dv M_UDFFID 312UDF file IDs. 313.It Dv M_AGP 314AGP memory. 315.It Dv M_DRM 316Direct Rendering Manager. 317.\" END DEFINES 318.El 319.Sh CONTEXT 320.Fn malloc 321and 322.Fn mallocarray 323can be called during autoconf, from process context, or from interrupt context 324if 325.Dv M_NOWAIT 326is passed via 327.Fa flags . 328They can't be called from interrupt context if 329.Dv M_WAITOK 330is passed via 331.Fa flags . 332.Pp 333.Fn free 334can be called during autoconf, from process context, or from interrupt context. 335.Sh RETURN VALUES 336.Fn malloc 337and 338.Fn mallocarray 339return a kernel virtual address that is suitably aligned for storage of 340any type of object. 341.Sh DIAGNOSTICS 342A kernel compiled with the 343.Dv DIAGNOSTIC 344configuration option attempts to detect memory corruption caused by 345such things as writing outside the allocated area and unbalanced calls to 346.Fn malloc 347or 348.Fn mallocarray , 349and 350.Fn free . 351Failing consistency checks will cause a panic or a system console message: 352.Pp 353.Bl -bullet -offset indent -compact 354.It 355panic: 356.Dq malloc: bogus type 357.It 358panic: 359.Dq malloc: out of space in kmem_map 360.It 361panic: 362.Dq malloc: allocation too large 363.It 364panic: 365.Dq malloc: wrong bucket 366.It 367panic: 368.Dq malloc: lost data 369.It 370panic: 371.Dq mallocarray: overflow 372.It 373panic: 374.Dq free: unaligned addr 375.It 376panic: 377.Dq free: duplicated free 378.It 379panic: 380.Dq free: multiple frees 381.It 382panic: 383.Dq free: non-malloced addr 384.It 385panic: 386.Dq free: size too large 387.It 388panic: 389.Dq free: size too small 390.It 391panic: 392.Dq kmeminit: minbucket too small/struct freelist too big 393.It 394.Dq multiply freed item Aq addr 395.It 396.Dq Data modified on freelist: Aq data object description 397.El 398.Sh SEE ALSO 399.Xr systat 1 , 400.Xr vmstat 8 401