1/* alloca.c -- allocate automatically reclaimed memory
2   (Mostly) portable public-domain implementation -- D A Gwyn
3
4   This implementation of the PWB library alloca function,
5   which is used to allocate space off the run-time stack so
6   that it is automatically reclaimed upon procedure exit,
7   was inspired by discussions with J. Q. Johnson of Cornell.
8   J.Otto Tennant <jot@cray.com> contributed the Cray support.
9
10   There are some preprocessor constants that can
11   be defined when compiling for your specific system, for
12   improved efficiency; however, the defaults should be okay.
13
14   The general concept of this implementation is to keep
15   track of all alloca-allocated blocks, and reclaim any
16   that are found to be deeper in the stack than the current
17   invocation.  This heuristic does not reclaim storage as
18   soon as it becomes invalid, but it will do so eventually.
19
20   As a special case, alloca(0) reclaims storage without
21   allocating any.  It is a good idea to use alloca(0) in
22   your main control loop, etc. to force garbage collection.  */
23
24#ifdef HAVE_CONFIG_H
25#include <config.h>
26#endif
27
28#ifdef HAVE_STRING_H
29#include <string.h>
30#endif
31#ifdef HAVE_STDLIB_H
32#include <stdlib.h>
33#endif
34
35#ifdef emacs
36#include "blockinput.h"
37#endif
38
39/* If compiling with GCC 2, this file's not needed.  Except of course if
40   the C alloca is explicitly requested.  */
41#if defined (USE_C_ALLOCA) || !defined (__GNUC__) || __GNUC__ < 2
42
43/* If someone has defined alloca as a macro,
44   there must be some other way alloca is supposed to work.  */
45#ifndef alloca
46
47#ifdef emacs
48#ifdef static
49/* actually, only want this if static is defined as ""
50   -- this is for usg, in which emacs must undefine static
51   in order to make unexec workable
52   */
53#ifndef STACK_DIRECTION
54you
55lose
56-- must know STACK_DIRECTION at compile-time
57#endif /* STACK_DIRECTION undefined */
58#endif /* static */
59#endif /* emacs */
60
61/* If your stack is a linked list of frames, you have to
62   provide an "address metric" ADDRESS_FUNCTION macro.  */
63
64#if defined (CRAY) && defined (CRAY_STACKSEG_END)
65long i00afunc ();
66#define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
67#else
68#define ADDRESS_FUNCTION(arg) &(arg)
69#endif
70
71#if __STDC__
72typedef void *pointer;
73#else
74typedef char *pointer;
75#endif
76
77#ifndef NULL
78#define	NULL	0
79#endif
80
81/* Different portions of Emacs need to call different versions of
82   malloc.  The Emacs executable needs alloca to call xmalloc, because
83   ordinary malloc isn't protected from input signals.  On the other
84   hand, the utilities in lib-src need alloca to call malloc; some of
85   them are very simple, and don't have an xmalloc routine.
86
87   Non-Emacs programs expect this to call use xmalloc.
88
89   Callers below should use malloc.  */
90
91#ifndef emacs
92#define malloc xmalloc
93#endif
94extern pointer malloc ();
95
96/* Define STACK_DIRECTION if you know the direction of stack
97   growth for your system; otherwise it will be automatically
98   deduced at run-time.
99
100   STACK_DIRECTION > 0 => grows toward higher addresses
101   STACK_DIRECTION < 0 => grows toward lower addresses
102   STACK_DIRECTION = 0 => direction of growth unknown  */
103
104#ifndef STACK_DIRECTION
105#define	STACK_DIRECTION	0	/* Direction unknown.  */
106#endif
107
108#if STACK_DIRECTION != 0
109
110#define	STACK_DIR	STACK_DIRECTION	/* Known at compile-time.  */
111
112#else /* STACK_DIRECTION == 0; need run-time code.  */
113
114static int stack_dir;		/* 1 or -1 once known.  */
115#define	STACK_DIR	stack_dir
116
117static void
118find_stack_direction ()
119{
120  static char *addr = NULL;	/* Address of first `dummy', once known.  */
121  auto char dummy;		/* To get stack address.  */
122
123  if (addr == NULL)
124    {				/* Initial entry.  */
125      addr = ADDRESS_FUNCTION (dummy);
126
127      find_stack_direction ();	/* Recurse once.  */
128    }
129  else
130    {
131      /* Second entry.  */
132      if (ADDRESS_FUNCTION (dummy) > addr)
133	stack_dir = 1;		/* Stack grew upward.  */
134      else
135	stack_dir = -1;		/* Stack grew downward.  */
136    }
137}
138
139#endif /* STACK_DIRECTION == 0 */
140
141/* An "alloca header" is used to:
142   (a) chain together all alloca'ed blocks;
143   (b) keep track of stack depth.
144
145   It is very important that sizeof(header) agree with malloc
146   alignment chunk size.  The following default should work okay.  */
147
148#ifndef	ALIGN_SIZE
149#define	ALIGN_SIZE	sizeof(double)
150#endif
151
152typedef union hdr
153{
154  char align[ALIGN_SIZE];	/* To force sizeof(header).  */
155  struct
156    {
157      union hdr *next;		/* For chaining headers.  */
158      char *deep;		/* For stack depth measure.  */
159    } h;
160} header;
161
162static header *last_alloca_header = NULL;	/* -> last alloca header.  */
163
164/* Return a pointer to at least SIZE bytes of storage,
165   which will be automatically reclaimed upon exit from
166   the procedure that called alloca.  Originally, this space
167   was supposed to be taken from the current stack frame of the
168   caller, but that method cannot be made to work for some
169   implementations of C, for example under Gould's UTX/32.  */
170
171pointer
172alloca (size)
173     unsigned size;
174{
175  auto char probe;		/* Probes stack depth: */
176  register char *depth = ADDRESS_FUNCTION (probe);
177
178#if STACK_DIRECTION == 0
179  if (STACK_DIR == 0)		/* Unknown growth direction.  */
180    find_stack_direction ();
181#endif
182
183  /* Reclaim garbage, defined as all alloca'd storage that
184     was allocated from deeper in the stack than currently.  */
185
186  {
187    register header *hp;	/* Traverses linked list.  */
188
189#ifdef emacs
190    BLOCK_INPUT;
191#endif
192
193    for (hp = last_alloca_header; hp != NULL;)
194      if ((STACK_DIR > 0 && hp->h.deep > depth)
195	  || (STACK_DIR < 0 && hp->h.deep < depth))
196	{
197	  register header *np = hp->h.next;
198
199	  free ((pointer) hp);	/* Collect garbage.  */
200
201	  hp = np;		/* -> next header.  */
202	}
203      else
204	break;			/* Rest are not deeper.  */
205
206    last_alloca_header = hp;	/* -> last valid storage.  */
207
208#ifdef emacs
209    UNBLOCK_INPUT;
210#endif
211  }
212
213  if (size == 0)
214    return NULL;		/* No allocation required.  */
215
216  /* Allocate combined header + user data storage.  */
217
218  {
219    register pointer new = malloc (sizeof (header) + size);
220    /* Address of header.  */
221
222    if (new == 0)
223      abort();
224
225    ((header *) new)->h.next = last_alloca_header;
226    ((header *) new)->h.deep = depth;
227
228    last_alloca_header = (header *) new;
229
230    /* User storage begins just after header.  */
231
232    return (pointer) ((char *) new + sizeof (header));
233  }
234}
235
236#if defined (CRAY) && defined (CRAY_STACKSEG_END)
237
238#ifdef DEBUG_I00AFUNC
239#include <stdio.h>
240#endif
241
242#ifndef CRAY_STACK
243#define CRAY_STACK
244#ifndef CRAY2
245/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
246struct stack_control_header
247  {
248    long shgrow:32;		/* Number of times stack has grown.  */
249    long shaseg:32;		/* Size of increments to stack.  */
250    long shhwm:32;		/* High water mark of stack.  */
251    long shsize:32;		/* Current size of stack (all segments).  */
252  };
253
254/* The stack segment linkage control information occurs at
255   the high-address end of a stack segment.  (The stack
256   grows from low addresses to high addresses.)  The initial
257   part of the stack segment linkage control information is
258   0200 (octal) words.  This provides for register storage
259   for the routine which overflows the stack.  */
260
261struct stack_segment_linkage
262  {
263    long ss[0200];		/* 0200 overflow words.  */
264    long sssize:32;		/* Number of words in this segment.  */
265    long ssbase:32;		/* Offset to stack base.  */
266    long:32;
267    long sspseg:32;		/* Offset to linkage control of previous
268				   segment of stack.  */
269    long:32;
270    long sstcpt:32;		/* Pointer to task common address block.  */
271    long sscsnm;		/* Private control structure number for
272				   microtasking.  */
273    long ssusr1;		/* Reserved for user.  */
274    long ssusr2;		/* Reserved for user.  */
275    long sstpid;		/* Process ID for pid based multi-tasking.  */
276    long ssgvup;		/* Pointer to multitasking thread giveup.  */
277    long sscray[7];		/* Reserved for Cray Research.  */
278    long ssa0;
279    long ssa1;
280    long ssa2;
281    long ssa3;
282    long ssa4;
283    long ssa5;
284    long ssa6;
285    long ssa7;
286    long sss0;
287    long sss1;
288    long sss2;
289    long sss3;
290    long sss4;
291    long sss5;
292    long sss6;
293    long sss7;
294  };
295
296#else /* CRAY2 */
297/* The following structure defines the vector of words
298   returned by the STKSTAT library routine.  */
299struct stk_stat
300  {
301    long now;			/* Current total stack size.  */
302    long maxc;			/* Amount of contiguous space which would
303				   be required to satisfy the maximum
304				   stack demand to date.  */
305    long high_water;		/* Stack high-water mark.  */
306    long overflows;		/* Number of stack overflow ($STKOFEN) calls.  */
307    long hits;			/* Number of internal buffer hits.  */
308    long extends;		/* Number of block extensions.  */
309    long stko_mallocs;		/* Block allocations by $STKOFEN.  */
310    long underflows;		/* Number of stack underflow calls ($STKRETN).  */
311    long stko_free;		/* Number of deallocations by $STKRETN.  */
312    long stkm_free;		/* Number of deallocations by $STKMRET.  */
313    long segments;		/* Current number of stack segments.  */
314    long maxs;			/* Maximum number of stack segments so far.  */
315    long pad_size;		/* Stack pad size.  */
316    long current_address;	/* Current stack segment address.  */
317    long current_size;		/* Current stack segment size.  This
318				   number is actually corrupted by STKSTAT to
319				   include the fifteen word trailer area.  */
320    long initial_address;	/* Address of initial segment.  */
321    long initial_size;		/* Size of initial segment.  */
322  };
323
324/* The following structure describes the data structure which trails
325   any stack segment.  I think that the description in 'asdef' is
326   out of date.  I only describe the parts that I am sure about.  */
327
328struct stk_trailer
329  {
330    long this_address;		/* Address of this block.  */
331    long this_size;		/* Size of this block (does not include
332				   this trailer).  */
333    long unknown2;
334    long unknown3;
335    long link;			/* Address of trailer block of previous
336				   segment.  */
337    long unknown5;
338    long unknown6;
339    long unknown7;
340    long unknown8;
341    long unknown9;
342    long unknown10;
343    long unknown11;
344    long unknown12;
345    long unknown13;
346    long unknown14;
347  };
348
349#endif /* CRAY2 */
350#endif /* not CRAY_STACK */
351
352#ifdef CRAY2
353/* Determine a "stack measure" for an arbitrary ADDRESS.
354   I doubt that "lint" will like this much.  */
355
356static long
357i00afunc (long *address)
358{
359  struct stk_stat status;
360  struct stk_trailer *trailer;
361  long *block, size;
362  long result = 0;
363
364  /* We want to iterate through all of the segments.  The first
365     step is to get the stack status structure.  We could do this
366     more quickly and more directly, perhaps, by referencing the
367     $LM00 common block, but I know that this works.  */
368
369  STKSTAT (&status);
370
371  /* Set up the iteration.  */
372
373  trailer = (struct stk_trailer *) (status.current_address
374				    + status.current_size
375				    - 15);
376
377  /* There must be at least one stack segment.  Therefore it is
378     a fatal error if "trailer" is null.  */
379
380  if (trailer == 0)
381    abort ();
382
383  /* Discard segments that do not contain our argument address.  */
384
385  while (trailer != 0)
386    {
387      block = (long *) trailer->this_address;
388      size = trailer->this_size;
389      if (block == 0 || size == 0)
390	abort ();
391      trailer = (struct stk_trailer *) trailer->link;
392      if ((block <= address) && (address < (block + size)))
393	break;
394    }
395
396  /* Set the result to the offset in this segment and add the sizes
397     of all predecessor segments.  */
398
399  result = address - block;
400
401  if (trailer == 0)
402    {
403      return result;
404    }
405
406  do
407    {
408      if (trailer->this_size <= 0)
409	abort ();
410      result += trailer->this_size;
411      trailer = (struct stk_trailer *) trailer->link;
412    }
413  while (trailer != 0);
414
415  /* We are done.  Note that if you present a bogus address (one
416     not in any segment), you will get a different number back, formed
417     from subtracting the address of the first block.  This is probably
418     not what you want.  */
419
420  return (result);
421}
422
423#else /* not CRAY2 */
424/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
425   Determine the number of the cell within the stack,
426   given the address of the cell.  The purpose of this
427   routine is to linearize, in some sense, stack addresses
428   for alloca.  */
429
430static long
431i00afunc (long address)
432{
433  long stkl = 0;
434
435  long size, pseg, this_segment, stack;
436  long result = 0;
437
438  struct stack_segment_linkage *ssptr;
439
440  /* Register B67 contains the address of the end of the
441     current stack segment.  If you (as a subprogram) store
442     your registers on the stack and find that you are past
443     the contents of B67, you have overflowed the segment.
444
445     B67 also points to the stack segment linkage control
446     area, which is what we are really interested in.  */
447
448  stkl = CRAY_STACKSEG_END ();
449  ssptr = (struct stack_segment_linkage *) stkl;
450
451  /* If one subtracts 'size' from the end of the segment,
452     one has the address of the first word of the segment.
453
454     If this is not the first segment, 'pseg' will be
455     nonzero.  */
456
457  pseg = ssptr->sspseg;
458  size = ssptr->sssize;
459
460  this_segment = stkl - size;
461
462  /* It is possible that calling this routine itself caused
463     a stack overflow.  Discard stack segments which do not
464     contain the target address.  */
465
466  while (!(this_segment <= address && address <= stkl))
467    {
468#ifdef DEBUG_I00AFUNC
469      fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
470#endif
471      if (pseg == 0)
472	break;
473      stkl = stkl - pseg;
474      ssptr = (struct stack_segment_linkage *) stkl;
475      size = ssptr->sssize;
476      pseg = ssptr->sspseg;
477      this_segment = stkl - size;
478    }
479
480  result = address - this_segment;
481
482  /* If you subtract pseg from the current end of the stack,
483     you get the address of the previous stack segment's end.
484     This seems a little convoluted to me, but I'll bet you save
485     a cycle somewhere.  */
486
487  while (pseg != 0)
488    {
489#ifdef DEBUG_I00AFUNC
490      fprintf (stderr, "%011o %011o\n", pseg, size);
491#endif
492      stkl = stkl - pseg;
493      ssptr = (struct stack_segment_linkage *) stkl;
494      size = ssptr->sssize;
495      pseg = ssptr->sspseg;
496      result += size;
497    }
498  return (result);
499}
500
501#endif /* not CRAY2 */
502#endif /* CRAY */
503
504#endif /* no alloca */
505#endif /* not GCC version 2 */
506