84a3e2e1fe
* lib/stdlib/alloca.c: Add `taken from binutils' and copyright line to alloca.c for minor changes.
103 lines
3.1 KiB
C
103 lines
3.1 KiB
C
/* alloca.c -- allocate automatically reclaimed memory
|
|
(Mostly) portable public-domain implementation -- D A Gwyn
|
|
|
|
Taken from GNU binutils 2.10.1.
|
|
Minor changes
|
|
Copyright © 2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
|
|
|
|
This implementation of the PWB library alloca function,
|
|
which is used to allocate space off the run-time stack so
|
|
that it is automatically reclaimed upon procedure exit,
|
|
was inspired by discussions with J. Q. Johnson of Cornell.
|
|
|
|
There are some preprocessor constants that can
|
|
be defined when compiling for your specific system, for
|
|
improved efficiency; however, the defaults should be okay.
|
|
|
|
The general concept of this implementation is to keep
|
|
track of all alloca-allocated blocks, and reclaim any
|
|
that are found to be deeper in the stack than the current
|
|
invocation. This heuristic does not reclaim storage as
|
|
soon as it becomes invalid, but it will do so eventually.
|
|
|
|
As a special case, alloca(0) reclaims storage without
|
|
allocating any. It is a good idea to use alloca(0) in
|
|
your main control loop, etc. to force garbage collection. */
|
|
|
|
#include <unistd.h>
|
|
|
|
#define ALIGN_SIZE 4
|
|
#define ADDRESS_FUNCTION(arg) &(arg)
|
|
#define STACK_DIR -1
|
|
|
|
union alloca_header
|
|
{
|
|
char align[ALIGN_SIZE]; /* To force sizeof(union alloca_header). */
|
|
struct
|
|
{
|
|
union alloca_header *next; /* For chaining headers. */
|
|
char *deep; /* For stack depth measure. */
|
|
} h;
|
|
};
|
|
|
|
static union alloca_header *last_alloca_header = NULL; /* -> last alloca header. */
|
|
|
|
/* Return a void * to at least SIZE bytes of storage,
|
|
which will be automatically reclaimed upon exit from
|
|
the procedure that called alloca. Originally, this space
|
|
was supposed to be taken from the current stack frame of the
|
|
caller, but that method cannot be made to work for some
|
|
implementations of C, for example under Gould's UTX/32. */
|
|
|
|
void *
|
|
alloca (size_t size)
|
|
{
|
|
char probe; /* Probes stack depth: */
|
|
char *depth = ADDRESS_FUNCTION (probe);
|
|
|
|
/* Reclaim garbage, defined as all alloca'd storage that
|
|
was allocated from deeper in the stack than currently. */
|
|
|
|
{
|
|
union alloca_header *hp; /* Traverses linked list. */
|
|
|
|
for (hp = last_alloca_header; hp != NULL;)
|
|
if ((STACK_DIR > 0 && hp->h.deep > depth)
|
|
|| (STACK_DIR < 0 && hp->h.deep < depth))
|
|
{
|
|
union alloca_header *np = hp->h.next;
|
|
|
|
free ((void *) hp); /* Collect garbage. */
|
|
|
|
hp = np; /* -> next header. */
|
|
}
|
|
else
|
|
break; /* Rest are not deeper. */
|
|
|
|
last_alloca_header = hp; /* -> last valid storage. */
|
|
|
|
}
|
|
|
|
if (size == 0)
|
|
return NULL; /* No allocation required. */
|
|
|
|
/* Allocate combined header + user data storage. */
|
|
|
|
{
|
|
void * new = malloc (sizeof (union alloca_header) + size);
|
|
/* Address of header. */
|
|
|
|
if (new == 0)
|
|
abort();
|
|
|
|
((union alloca_header *) new)->h.next = last_alloca_header;
|
|
((union alloca_header *) new)->h.deep = depth;
|
|
|
|
last_alloca_header = (union alloca_header *) new;
|
|
|
|
/* User storage begins just after header. */
|
|
|
|
return (void *) ((char *) new + sizeof (union alloca_header));
|
|
}
|
|
}
|