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