1.\" $OpenBSD: malloc.9,v 1.64 2017/10/27 16:11:00 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: October 27 2017 $ 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_DEBUG 156.Nm malloc 157debug structures. 158.It Dv M_PCB 159Protocol control blocks. 160.It Dv M_RTABLE 161Routing tables. 162.It Dv M_IFADDR 163Interface addresses. 164.It Dv M_SOOPTS 165Socket options. 166.It Dv M_SYSCTL 167Sysctl persistent buffers. 168.It Dv M_COUNTERS 169Per-CPU Counters for use via 170.Xr counters_alloc 9 . 171.It Dv M_IOCTLOPS 172Ioctl data buffers. 173.It Dv M_IOV 174Large IOVs. 175.It Dv M_MOUNT 176VFS mount structs. 177.It Dv M_NFSREQ 178NFS request headers. 179.It Dv M_NFSMNT 180NFS mount structures. 181.It Dv M_VNODE 182Dynamically allocated vnodes. 183.It Dv M_CACHE 184Dynamically allocated cache entries. 185.It Dv M_DQUOT 186UFS quota entries. 187.It Dv M_UFSMNT 188UFS mount structures. 189.It Dv M_SHM 190SVID compatible shared memory segments. 191.It Dv M_VMMAP 192VM map structures. 193.It Dv M_SEM 194SVID compatible semaphores. 195.It Dv M_DIRHASH 196UFS directory hash structures. 197.It Dv M_ACPI 198ACPI structures. 199.It Dv M_VMPMAP 200VM pmap data. 201.It Dv M_FILE 202Open file structures. 203.It Dv M_FILEDESC 204Open file descriptor tables. 205.It Dv M_PROC 206Proc structures. 207.It Dv M_SUBPROC 208Proc sub-structures. 209.It Dv M_VCLUSTER 210Cluster for VFS. 211.It Dv M_MFSNODE 212MFS vnode private part. 213.It Dv M_NETADDR 214Export host address structures. 215.It Dv M_NFSSVC 216NFS server structures. 217.It Dv M_NFSD 218NFS server daemon structures. 219.It Dv M_IPMOPTS 220Internet multicast options. 221.It Dv M_IPMADDR 222Internet multicast addresses. 223.It Dv M_IFMADDR 224Link-level multicast addresses. 225.It Dv M_MRTABLE 226Multicast routing tables. 227.It Dv M_ISOFSMNT 228ISOFS mount structures. 229.It Dv M_ISOFSNODE 230ISOFS vnode private part. 231.It Dv M_MSDOSFSMNT 232MSDOS FS mount structures. 233.It Dv M_MSDOSFSFAT 234MSDOS FS FAT tables. 235.It Dv M_MSDOSFSNODE 236MSDOS FS vnode private part. 237.It Dv M_TTYS 238Allocated tty structures. 239.It Dv M_EXEC 240Argument lists & other mem used by exec. 241.It Dv M_MISCFSMNT 242Miscellaneous FS mount structures. 243.It Dv M_FUSEFS 244FUSE FS mount structures. 245.It Dv M_PFKEY 246Pfkey data. 247.It Dv M_TDB 248Transforms database. 249.It Dv M_XDATA 250IPsec data. 251.It Dv M_PAGEDEP 252File page dependencies. 253.It Dv M_INODEDEP 254Inode dependencies. 255.It Dv M_NEWBLK 256New block allocation. 257.It Dv M_INDIRDEP 258Indirect block dependencies. 259.It Dv M_VMSWAP 260VM swap structures. 261.It Dv M_UVMAMAP 262UVM amap and related. 263.It Dv M_UVMAOBJ 264UVM aobj and related. 265.It Dv M_USB 266USB general. 267.It Dv M_USBDEV 268USB device driver. 269.It Dv M_USBHC 270USB host controller. 271.It Dv M_MEMDESC 272Memory range. 273.It Dv M_CRYPTO_DATA 274.Xr crypto 9 275data buffers. 276.It Dv M_CREDENTIALS 277.Xr ipsec 4 278related credentials. 279.It Dv M_EMULDATA 280Per process emulation data. 281.It Dv M_IP6OPT 282IPv6 options. 283.It Dv M_IP6NDP 284IPv6 neighbour discovery structures. 285.It Dv M_TEMP 286Miscellaneous temporary data buffers. 287.It Dv M_NTFSMNT 288NTFS mount structures. 289.It Dv M_NTFSNTNODE 290NTFS ntnode information. 291.It Dv M_NTFSNODE 292NTFS fnode information. 293.It Dv M_NTFSDIR 294NTFS directory buffers. 295.It Dv M_NTFSHASH 296NTFS ntnode hash tables. 297.It Dv M_NTFSVATTR 298NTFS file attribute information. 299.It Dv M_NTFSRDATA 300NTFS resident data. 301.It Dv M_NTFSDECOMP 302NTFS decompression temporary storage. 303.It Dv M_NTFSRUN 304NTFS vrun storage. 305.It Dv M_KEVENT 306.Xr kqueue 2 307data structures. 308.It Dv M_UDFMOUNT 309UDF mount structures. 310.It Dv M_UDFFENTRY 311UDF file entries. 312.It Dv M_UDFFID 313UDF file ID. 314.It Dv M_AGP 315AGP memory. 316.It Dv M_DRM 317Direct Rendering Manager. 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 DEBUGGING 399A kernel compiled with the 400.Cm MALLOC_DEBUG 401option allows for more extensive debugging of memory allocations. 402The 403.Va debug_malloc_type , 404.Va debug_malloc_size , 405.Va debug_malloc_size_lo 406and 407.Va debug_malloc_size_hi 408variables choose which allocation to debug. 409.Va debug_malloc_type 410should be set to the memory type and 411.Va debug_malloc_size 412should be set to the memory size to debug. 4130 can be used as a wildcard. 414.Va debug_malloc_size_lo 415and 416.Va debug_malloc_size_hi 417can be used to specify a range of sizes if the exact size to debug is not 418known. 419When those are used, 420.Va debug_malloc_size 421needs to be set to the wildcard. 422.Dv M_DEBUG 423can also be specified as an allocation type to force allocation with 424debugging. 425.Pp 426Every call to 427.Fn malloc 428or 429.Fn mallocarray 430with a memory type and size that matches the debugged type and size will 431allocate two virtual pages. 432The pointer returned will be aligned so that 433the requested area will end at the page boundary and the second virtual page 434will be left unmapped. 435This way we can catch reads and writes outside the allocated area. 436.Pp 437Every call to 438.Fn free 439with memory that was returned by the debugging allocators will cause the memory 440area to become unmapped so that we can catch dangling reads and writes to 441freed memory. 442.Pp 443There are no special diagnostics if any errors are caught by the debugging 444malloc. 445The errors will look like normal access to unmapped memory. 446On a memory access error, the 447.Ic show malloc 448command in 449.Xr ddb 4 450can be invoked to see what memory areas are allocated and freed. 451If the faulting address is within two pages from an address on the allocated 452list, there was an access outside the allocated area. 453If the faulting address is within two pages from an address on the free list, 454there was an access to freed memory. 455.Pp 456Care needs to be taken when using the 457.Cm MALLOC_DEBUG 458option: the memory consumption can run away pretty quickly and there is 459a severe performance degradation when allocating and freeing debugged memory 460types. 461.Sh SEE ALSO 462.Xr systat 1 , 463.Xr vmstat 8 464