1.\" $OpenBSD: malloc.9,v 1.69 2023/03/17 19:44:15 millert 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: March 17 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.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_LOG 177Messages in kernel log stash. 178.It Dv M_VNODE 179Dynamically allocated vnodes. 180.It Dv M_DQUOT 181UFS quota entries. 182.It Dv M_UFSMNT 183UFS mount structures. 184.It Dv M_SHM 185SVID compatible shared memory segments. 186.It Dv M_VMMAP 187VM map structures. 188.It Dv M_SEM 189SVID compatible semaphores. 190.It Dv M_DIRHASH 191UFS directory hash structures. 192.It Dv M_ACPI 193ACPI structures. 194.It Dv M_VMPMAP 195VM pmap data. 196.It Dv M_FILEDESC 197Open file descriptor tables. 198.It Dv M_SIGIO 199Sigio structures. 200.It Dv M_PROC 201Proc structures. 202.It Dv M_SUBPROC 203Proc sub-structures. 204.It Dv M_MFSNODE 205MFS vnode private part. 206.It Dv M_NETADDR 207Export host address structures. 208.It Dv M_NFSSVC 209NFS server structures. 210.It Dv M_NFSD 211NFS server daemon structures. 212.It Dv M_IPMOPTS 213Internet multicast options. 214.It Dv M_IPMADDR 215Internet multicast addresses. 216.It Dv M_IFMADDR 217Link-level multicast addresses. 218.It Dv M_MRTABLE 219Multicast routing tables. 220.It Dv M_ISOFSMNT 221ISOFS mount structures. 222.It Dv M_ISOFSNODE 223ISOFS vnode private part. 224.It Dv M_MSDOSFSMNT 225MSDOS FS mount structures. 226.It Dv M_MSDOSFSFAT 227MSDOS FS FAT tables. 228.It Dv M_MSDOSFSNODE 229MSDOS FS vnode private part. 230.It Dv M_TTYS 231Allocated tty structures. 232.It Dv M_EXEC 233Argument lists & other mem used by exec. 234.It Dv M_MISCFSMNT 235Miscellaneous FS mount structures. 236.It Dv M_FUSEFS 237FUSE FS mount structures. 238.It Dv M_PFKEY 239Pfkey data. 240.It Dv M_TDB 241Transforms database. 242.It Dv M_XDATA 243IPsec data. 244.It Dv M_PAGEDEP 245File page dependencies. 246.It Dv M_INODEDEP 247Inode dependencies. 248.It Dv M_NEWBLK 249New block allocation. 250.It Dv M_INDIRDEP 251Indirect block dependencies. 252.It Dv M_VMSWAP 253VM swap structures. 254.It Dv M_UVMAMAP 255UVM amap and related. 256.It Dv M_UVMAOBJ 257UVM aobj and related. 258.It Dv M_USB 259USB general. 260.It Dv M_USBDEV 261USB device driver. 262.It Dv M_USBHC 263USB host controller. 264.It Dv M_WITNESS 265.Xr witness 4 266memory. 267.It Dv M_MEMDESC 268Memory range. 269.It Dv M_CRYPTO_DATA 270.Xr crypto 9 271data buffers. 272.It Dv M_CREDENTIALS 273.Xr ipsec 4 274related credentials. 275.It Dv M_IP6OPT 276IPv6 options. 277.It Dv M_IP6NDP 278IPv6 neighbour discovery structures. 279.It Dv M_TEMP 280Miscellaneous temporary data buffers. 281.It Dv M_NTFSMNT 282NTFS mount structures. 283.It Dv M_NTFSNTNODE 284NTFS ntnode information. 285.It Dv M_NTFSFNODE 286NTFS fnode information. 287.It Dv M_NTFSDIR 288NTFS directory buffers. 289.It Dv M_NTFSNTHASH 290NTFS ntnode hash tables. 291.It Dv M_NTFSNTVATTR 292NTFS file attribute information. 293.It Dv M_NTFSRDATA 294NTFS resident data. 295.It Dv M_NTFSDECOMP 296NTFS decompression temporary storage. 297.It Dv M_NTFSRUN 298NTFS vrun storage. 299.It Dv M_KEVENT 300.Xr kqueue 2 301data structures. 302.It Dv M_SYNCACHE 303SYN cache hash array. 304.It Dv M_UDFMOUNT 305UDF mount structures. 306.It Dv M_UDFFENTRY 307UDF file entries. 308.It Dv M_UDFFID 309UDF file ID. 310.It Dv M_AGP 311AGP memory. 312.It Dv M_DRM 313Direct Rendering Manager. 314.El 315.Sh CONTEXT 316.Fn malloc 317and 318.Fn mallocarray 319can be called during autoconf, from process context, or from interrupt context 320if 321.Dv M_NOWAIT 322is passed via 323.Fa flags . 324They can't be called from interrupt context if 325.Dv M_WAITOK 326is passed via 327.Fa flags . 328.Pp 329.Fn free 330can be called during autoconf, from process context, or from interrupt context. 331.Sh RETURN VALUES 332.Fn malloc 333and 334.Fn mallocarray 335return a kernel virtual address that is suitably aligned for storage of 336any type of object. 337.Sh DIAGNOSTICS 338A kernel compiled with the 339.Dv DIAGNOSTIC 340configuration option attempts to detect memory corruption caused by 341such things as writing outside the allocated area and unbalanced calls to 342.Fn malloc 343or 344.Fn mallocarray , 345and 346.Fn free . 347Failing consistency checks will cause a panic or a system console message: 348.Pp 349.Bl -bullet -offset indent -compact 350.It 351panic: 352.Dq malloc: bogus type 353.It 354panic: 355.Dq malloc: out of space in kmem_map 356.It 357panic: 358.Dq malloc: allocation too large 359.It 360panic: 361.Dq malloc: wrong bucket 362.It 363panic: 364.Dq malloc: lost data 365.It 366panic: 367.Dq mallocarray: overflow 368.It 369panic: 370.Dq free: unaligned addr 371.It 372panic: 373.Dq free: duplicated free 374.It 375panic: 376.Dq free: multiple frees 377.It 378panic: 379.Dq free: non-malloced addr 380.It 381panic: 382.Dq free: size too large 383.It 384panic: 385.Dq free: size too small 386.It 387panic: 388.Dq kmeminit: minbucket too small/struct freelist too big 389.It 390.Dq multiply freed item Aq addr 391.It 392.Dq Data modified on freelist: Aq data object description 393.El 394.Sh SEE ALSO 395.Xr systat 1 , 396.Xr vmstat 8 397