Malloc and free provide a simple memory allocation package. Malloc
returns a pointer to a new block of at least size bytes. The block
is suitably aligned for storage of any type of object. No two
active pointers from malloc will have the same value. The call
malloc(0) returns a valid pointer rather than null.
The argument to free is a pointer to a block previously allocated
by malloc; this space is made available for further allocation.
It is legal to free a null pointer; the effect is a no–op. The
contents of the space returned by malloc are undefined. Mallocz
behaves as malloc, except that if clr is non–zero, the memory
returned will be zeroed.
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 ptr to size
bytes and returns a pointer to the (possibly moved) block. The
contents will be unchanged up to the lesser of the new and old
sizes. Realloc takes on special meanings when one or both arguments
means malloc(size); returns a pointer to the newly–allocated memory|
means free(ptr); returns null|
Calloc allocates space for an array of nelem elements of size
elsize. The space is initialized to zeros. Free frees such a block.
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
Malloctopoolblock takes the address of a block returned by malloc
and returns the address of the corresponding block allocated by
the pool(2) routines.