Plan 9 /sys/man/9/malloc

NAME

malloc, mallocz, smalloc, realloc, calloc, free, msize, setmalloctag, setrealloctag, getmalloctag, getrealloctag, malloctopoolblock – kernel memory allocator

SYNOPSIS

void* malloc(ulong size)
void* mallocalign(ulong size, ulong align, long offset, ulong span)
void* mallocz(ulong size, int clr)
void* smalloc(ulong size)
void* realloc(void *p, ulong size)
void* calloc(ulong n, ulong szelem)
void    free(void *ptr)
ulong msize(void *ptr)
void    setmalloctag(void *ptr, ulong tag)
ulong getmalloctag(void *ptr)
void    setrealloctag(void *ptr, ulong tag)
ulong getrealloctag(void *ptr)
void* malloctopoolblock(void*)

DESCRIPTION

These are kernel versions of the functions in malloc(2). They allocate memory from the mainmem memory pool, which is managed by the allocator pool(2), which in turn replenishes the pool as required by calling xalloc(9). All but smalloc (which calls sleep(9)) may safely be called by interrupt handlers.
Malloc returns a pointer to a block of at least size bytes, initialised to zero. The block is suitably aligned for storage of any type of object. The call malloc(0) returns a valid pointer rather than null. Mallocz is similar, but only clears the memory if clr is non–zero.
Smalloc returns a pointer to a block of size bytes, initialised to zero. If the memory is not immediately available, smalloc retries every 100 milliseconds until the memory is acquired.
Mallocalign allocates a block of at least n bytes of memory respecting alignment contraints. If align is non–zero, the returned pointer is aligned to be equal to offset modulo align. If span is non–zero, the n byte block allocated will not span a span–byte boundary.
Realloc changes the size of the block pointed to by p to size bytes, if possible without moving the data, and returns a pointer to the block. The contents are unchanged up to the lesser of old and new sizes, and any new space allocated is initialised to zero. Realloc takes on special meanings when one or both arguments are zero:
realloc(0, size)
means malloc(size); returns a pointer to the newly–allocated memory

realloc(ptr, 0)
means free(ptr); returns null

realloc(0, 0)
no–op; returns null

Calloc returns a pointer to a block of memory of at least n*szelem bytes, initialised to zero. New code should use mallocz instead.
The argument to free is a pointer to a block of memory allocated by one of the routines above, which is returned to the allocation pool, or a null pointer, which is ignored.
When a block is allocated, sometimes there is some extra unused space at the end. Msize grows the block to encompass this unused space and returns the new number of bytes that may be used.
The memory allocator maintains two word–sized fields associated with each block, the ``malloc tag'' and the ``realloc tag''. By convention, the malloc tag is the PC that allocated the block, and the realloc tag the PC that last reallocated the block. These may be set or examined with setmalloctag, getmalloctag, setrealloctag, and getrealloctag. When allocating blocks directly with malloc and realloc, these tags will be set properly. If a custom allocator wrapper is used, the allocator wrapper can set the tags itself (usually by passing the result of getcallerpc(2) to setmalloctag) to provide more useful information about the source of allocation.
Malloctopoolblock takes the address of a block returned by malloc and returns the address of the corresponding block allocated by the pool(2) routines.

SOURCE

/sys/src/9/port/alloc.c

DIAGNOSTICS

All functions except smalloc return a null pointer if space is unavailable. If the allocated blocks have no malloc or realloc tags, getmalloctag and getrealloctag return ~0.


	malloc, mallocz, smalloc, realloc, calloc, free, msize, setmalloctag, setrealloctag, getmalloctag, getrealloctag, malloctopoolblock – kernel memory allocator


	All functions except smalloc return a null pointer if space is unavailable. If the allocated blocks have no malloc or realloc tags, getmalloctag and getrealloctag return `~0`.