/* alloca.c -- allocate automatically reclaimed memory
(Mostly) portable public-domain implementation -- D A Gwyn
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.
J.Otto Tennant <jot@cray.com> contributed the Cray support.
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 <config.h>
#include <alloca.h>
#include <string.h>
#include <stdlib.h>
#ifdef emacs
# include "lisp.h"
# include "blockinput.h"
# ifdef EMACS_FREE
# endif
#else
#endif
/* If compiling with GCC 2, this file's not needed. */
/* If someone has defined alloca as a macro,
there must be some other way alloca is supposed to work. */
# ifndef alloca
# ifdef emacs
# ifdef static
/* actually, only want this if static is defined as ""
-- this is for usg, in which emacs must undefine static
in order to make unexec workable
*/
# ifndef STACK_DIRECTION
/* Using #error here is not wise since this file should work for
old and obscure compilers. */
# endif /* STACK_DIRECTION undefined */
# endif /* static */
# endif /* emacs */
/* If your stack is a linked list of frames, you have to
provide an "address metric" ADDRESS_FUNCTION macro. */
# if defined (CRAY) && defined (CRAY_STACKSEG_END)
long i00afunc ();
# else
# endif
/* Define STACK_DIRECTION if you know the direction of stack
growth for your system; otherwise it will be automatically
deduced at run-time.
STACK_DIRECTION > 0 => grows toward higher addresses
STACK_DIRECTION < 0 => grows toward lower addresses
STACK_DIRECTION = 0 => direction of growth unknown */
# ifndef STACK_DIRECTION
# endif
# if STACK_DIRECTION != 0
# else /* STACK_DIRECTION == 0; need run-time code. */
static void
find_stack_direction (void)
{
{ /* Initial entry. */
find_stack_direction (); /* Recurse once. */
}
else
{
/* Second entry. */
else
}
}
# endif /* STACK_DIRECTION == 0 */
/* An "alloca header" is used to:
(a) chain together all alloca'ed blocks;
(b) keep track of stack depth.
It is very important that sizeof(header) agree with malloc
alignment chunk size. The following default should work okay. */
# ifndef ALIGN_SIZE
# define ALIGN_SIZE sizeof(double)
# endif
typedef union hdr
{
struct
{
} h;
} header;
/* Return a pointer 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 *
{
# if STACK_DIRECTION == 0
if (STACK_DIR == 0) /* Unknown growth direction. */
# endif
/* Reclaim garbage, defined as all alloca'd storage that
was allocated from deeper in the stack than currently. */
{
# ifdef emacs
# endif
{
}
else
break; /* Rest are not deeper. */
# ifdef emacs
# endif
}
if (size == 0)
return NULL; /* No allocation required. */
/* Allocate combined header + user data storage. */
{
/* Address of header. */
if (combined_size < sizeof (header))
memory_full ();
if (! new)
memory_full ();
/* User storage begins just after header. */
return (void *) (new + 1);
}
}
# if defined (CRAY) && defined (CRAY_STACKSEG_END)
# ifdef DEBUG_I00AFUNC
# include <stdio.h>
# endif
# ifndef CRAY_STACK
# define CRAY_STACK
# ifndef CRAY2
/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
struct stack_control_header
{
};
/* The stack segment linkage control information occurs at
the high-address end of a stack segment. (The stack
grows from low addresses to high addresses.) The initial
part of the stack segment linkage control information is
0200 (octal) words. This provides for register storage
for the routine which overflows the stack. */
struct stack_segment_linkage
{
long:32;
segment of stack. */
long:32;
microtasking. */
long ssa0;
long ssa1;
long ssa2;
long ssa3;
long ssa4;
long ssa5;
long ssa6;
long ssa7;
long sss0;
long sss1;
long sss2;
long sss3;
long sss4;
long sss5;
long sss6;
long sss7;
};
# else /* CRAY2 */
/* The following structure defines the vector of words
returned by the STKSTAT library routine. */
struct stk_stat
{
be required to satisfy the maximum
stack demand to date. */
number is actually corrupted by STKSTAT to
include the fifteen word trailer area. */
};
/* The following structure describes the data structure which trails
any stack segment. I think that the description in 'asdef' is
out of date. I only describe the parts that I am sure about. */
struct stk_trailer
{
this trailer). */
long unknown2;
long unknown3;
segment. */
long unknown5;
long unknown6;
long unknown7;
long unknown8;
long unknown9;
long unknown10;
long unknown11;
long unknown12;
long unknown13;
long unknown14;
};
# endif /* CRAY2 */
# endif /* not CRAY_STACK */
# ifdef CRAY2
/* Determine a "stack measure" for an arbitrary ADDRESS.
I doubt that "lint" will like this much. */
static long
{
long result = 0;
/* We want to iterate through all of the segments. The first
step is to get the stack status structure. We could do this
more quickly and more directly, perhaps, by referencing the
$LM00 common block, but I know that this works. */
/* Set up the iteration. */
- 15);
/* There must be at least one stack segment. Therefore it is
a fatal error if "trailer" is null. */
if (trailer == 0)
abort ();
/* Discard segments that do not contain our argument address. */
while (trailer != 0)
{
abort ();
break;
}
/* Set the result to the offset in this segment and add the sizes
of all predecessor segments. */
if (trailer == 0)
{
return result;
}
do
{
abort ();
}
while (trailer != 0);
/* We are done. Note that if you present a bogus address (one
not in any segment), you will get a different number back, formed
from subtracting the address of the first block. This is probably
not what you want. */
return (result);
}
# else /* not CRAY2 */
/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
Determine the number of the cell within the stack,
given the address of the cell. The purpose of this
routine is to linearize, in some sense, stack addresses
for alloca. */
static long
{
long stkl = 0;
long result = 0;
/* Register B67 contains the address of the end of the
current stack segment. If you (as a subprogram) store
your registers on the stack and find that you are past
the contents of B67, you have overflowed the segment.
B67 also points to the stack segment linkage control
area, which is what we are really interested in. */
stkl = CRAY_STACKSEG_END ();
/* If one subtracts 'size' from the end of the segment,
one has the address of the first word of the segment.
If this is not the first segment, 'pseg' will be
nonzero. */
/* It is possible that calling this routine itself caused
a stack overflow. Discard stack segments which do not
contain the target address. */
{
# ifdef DEBUG_I00AFUNC
# endif
if (pseg == 0)
break;
}
/* If you subtract pseg from the current end of the stack,
you get the address of the previous stack segment's end.
This seems a little convoluted to me, but I'll bet you save
a cycle somewhere. */
while (pseg != 0)
{
# ifdef DEBUG_I00AFUNC
# endif
}
return (result);
}
# endif /* not CRAY2 */
# endif /* CRAY */
# endif /* no alloca */
#endif /* not GCC version 3 */