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