1.\" $OpenBSD: malloc.9,v 1.66 2019/01/18 17:52:18 visa 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: January 18 2019 $ 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_SOOPTS 162Socket options. 163.It Dv M_SYSCTL 164Sysctl persistent buffers. 165.It Dv M_COUNTERS 166Per-CPU Counters for use via 167.Xr counters_alloc 9 . 168.It Dv M_IOCTLOPS 169Ioctl data buffers. 170.It Dv M_IOV 171Large IOVs. 172.It Dv M_MOUNT 173VFS mount structs. 174.It Dv M_NFSREQ 175NFS request headers. 176.It Dv M_NFSMNT 177NFS mount structures. 178.It Dv M_VNODE 179Dynamically allocated vnodes. 180.It Dv M_CACHE 181Dynamically allocated cache entries. 182.It Dv M_DQUOT 183UFS quota entries. 184.It Dv M_UFSMNT 185UFS mount structures. 186.It Dv M_SHM 187SVID compatible shared memory segments. 188.It Dv M_VMMAP 189VM map structures. 190.It Dv M_SEM 191SVID compatible semaphores. 192.It Dv M_DIRHASH 193UFS directory hash structures. 194.It Dv M_ACPI 195ACPI structures. 196.It Dv M_VMPMAP 197VM pmap data. 198.It Dv M_FILE 199Open file structures. 200.It Dv M_FILEDESC 201Open file descriptor tables. 202.It Dv M_SIGIO 203Sigio structures. 204.It Dv M_PROC 205Proc structures. 206.It Dv M_SUBPROC 207Proc sub-structures. 208.It Dv M_VCLUSTER 209Cluster for VFS. 210.It Dv M_MFSNODE 211MFS vnode private part. 212.It Dv M_NETADDR 213Export host address structures. 214.It Dv M_NFSSVC 215NFS server structures. 216.It Dv M_NFSD 217NFS server daemon structures. 218.It Dv M_IPMOPTS 219Internet multicast options. 220.It Dv M_IPMADDR 221Internet multicast addresses. 222.It Dv M_IFMADDR 223Link-level multicast addresses. 224.It Dv M_MRTABLE 225Multicast routing tables. 226.It Dv M_ISOFSMNT 227ISOFS mount structures. 228.It Dv M_ISOFSNODE 229ISOFS vnode private part. 230.It Dv M_MSDOSFSMNT 231MSDOS FS mount structures. 232.It Dv M_MSDOSFSFAT 233MSDOS FS FAT tables. 234.It Dv M_MSDOSFSNODE 235MSDOS FS vnode private part. 236.It Dv M_TTYS 237Allocated tty structures. 238.It Dv M_EXEC 239Argument lists & other mem used by exec. 240.It Dv M_MISCFSMNT 241Miscellaneous FS mount structures. 242.It Dv M_FUSEFS 243FUSE FS mount structures. 244.It Dv M_PFKEY 245Pfkey data. 246.It Dv M_TDB 247Transforms database. 248.It Dv M_XDATA 249IPsec data. 250.It Dv M_PAGEDEP 251File page dependencies. 252.It Dv M_INODEDEP 253Inode dependencies. 254.It Dv M_NEWBLK 255New block allocation. 256.It Dv M_INDIRDEP 257Indirect block dependencies. 258.It Dv M_VMSWAP 259VM swap structures. 260.It Dv M_UVMAMAP 261UVM amap and related. 262.It Dv M_UVMAOBJ 263UVM aobj and related. 264.It Dv M_USB 265USB general. 266.It Dv M_USBDEV 267USB device driver. 268.It Dv M_USBHC 269USB host controller. 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_EMULDATA 279Per process emulation data. 280.It Dv M_IP6OPT 281IPv6 options. 282.It Dv M_IP6NDP 283IPv6 neighbour discovery structures. 284.It Dv M_TEMP 285Miscellaneous temporary data buffers. 286.It Dv M_NTFSMNT 287NTFS mount structures. 288.It Dv M_NTFSNTNODE 289NTFS ntnode information. 290.It Dv M_NTFSFNODE 291NTFS fnode information. 292.It Dv M_NTFSDIR 293NTFS directory buffers. 294.It Dv M_NTFSNTHASH 295NTFS ntnode hash tables. 296.It Dv M_NTFSNTVATTR 297NTFS file attribute information. 298.It Dv M_NTFSRDATA 299NTFS resident data. 300.It Dv M_NTFSDECOMP 301NTFS decompression temporary storage. 302.It Dv M_NTFSRUN 303NTFS vrun storage. 304.It Dv M_KEVENT 305.Xr kqueue 2 306data structures. 307.It Dv M_SYNCACHE 308SYN cache hash array. 309.It Dv M_UDFMOUNT 310UDF mount structures. 311.It Dv M_UDFFENTRY 312UDF file entries. 313.It Dv M_UDFFID 314UDF file ID. 315.It Dv M_AGP 316AGP memory. 317.It Dv M_DRM 318Direct Rendering Manager. 319.El 320.Sh CONTEXT 321.Fn malloc 322and 323.Fn mallocarray 324can be called during autoconf, from process context, or from interrupt context 325if 326.Dv M_NOWAIT 327is passed via 328.Fa flags . 329They can't be called from interrupt context if 330.Dv M_WAITOK 331is passed via 332.Fa flags . 333.Pp 334.Fn free 335can be called during autoconf, from process context, or from interrupt context. 336.Sh RETURN VALUES 337.Fn malloc 338and 339.Fn mallocarray 340return a kernel virtual address that is suitably aligned for storage of 341any type of object. 342.Sh DIAGNOSTICS 343A kernel compiled with the 344.Dv DIAGNOSTIC 345configuration option attempts to detect memory corruption caused by 346such things as writing outside the allocated area and unbalanced calls to 347.Fn malloc 348or 349.Fn mallocarray , 350and 351.Fn free . 352Failing consistency checks will cause a panic or a system console message: 353.Pp 354.Bl -bullet -offset indent -compact 355.It 356panic: 357.Dq malloc: bogus type 358.It 359panic: 360.Dq malloc: out of space in kmem_map 361.It 362panic: 363.Dq malloc: allocation too large 364.It 365panic: 366.Dq malloc: wrong bucket 367.It 368panic: 369.Dq malloc: lost data 370.It 371panic: 372.Dq mallocarray: overflow 373.It 374panic: 375.Dq free: unaligned addr 376.It 377panic: 378.Dq free: duplicated free 379.It 380panic: 381.Dq free: multiple frees 382.It 383panic: 384.Dq free: non-malloced addr 385.It 386panic: 387.Dq free: size too large 388.It 389panic: 390.Dq free: size too small 391.It 392panic: 393.Dq kmeminit: minbucket too small/struct freelist too big 394.It 395.Dq multiply freed item Aq addr 396.It 397.Dq Data modified on freelist: Aq data object description 398.El 399.Sh SEE ALSO 400.Xr systat 1 , 401.Xr vmstat 8 402