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pcg |
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/* alloca.c -- allocate automatically reclaimed memory |
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(Mostly) portable public-domain implementation -- D A Gwyn |
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This implementation of the PWB library alloca function, |
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which is used to allocate space off the run-time stack so |
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that it is automatically reclaimed upon procedure exit, |
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was inspired by discussions with J. Q. Johnson of Cornell. |
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J.Otto Tennant <jot@cray.com> contributed the Cray support. |
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There are some preprocessor constants that can |
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be defined when compiling for your specific system, for |
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improved efficiency; however, the defaults should be okay. |
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The general concept of this implementation is to keep |
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track of all alloca-allocated blocks, and reclaim any |
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that are found to be deeper in the stack than the current |
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invocation. This heuristic does not reclaim storage as |
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soon as it becomes invalid, but it will do so eventually. |
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As a special case, alloca(0) reclaims storage without |
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allocating any. It is a good idea to use alloca(0) in |
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your main control loop, etc. to force garbage collection. */ |
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#ifdef HAVE_CONFIG_H |
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# include <config.h> |
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#endif |
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#ifdef emacs |
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# include "blockinput.h" |
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#endif |
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/* If compiling with GCC 2, this file's not needed. */ |
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#if !defined (__GNUC__) || __GNUC__ < 2 |
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/* If someone has defined alloca as a macro, |
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there must be some other way alloca is supposed to work. */ |
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# ifndef alloca |
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# ifdef emacs |
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# ifdef static |
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/* actually, only want this if static is defined as "" |
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-- this is for usg, in which emacs must undefine static |
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in order to make unexec workable |
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*/ |
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# ifndef STACK_DIRECTION |
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you |
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lose |
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-- must know STACK_DIRECTION at compile-time |
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# endif /* STACK_DIRECTION undefined */ |
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# endif /* static */ |
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# endif /* emacs */ |
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/* If your stack is a linked list of frames, you have to |
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provide an "address metric" ADDRESS_FUNCTION macro. */ |
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# if defined (CRAY) && defined (CRAY_STACKSEG_END) |
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long i00afunc (); |
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# define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) |
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# else |
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# define ADDRESS_FUNCTION(arg) &(arg) |
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# endif |
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# if __STDC__ |
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typedef void *pointer; |
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# else |
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typedef char *pointer; |
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# endif |
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# ifndef NULL |
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# define NULL 0 |
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# endif |
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/* Different portions of Emacs need to call different versions of |
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malloc. The Emacs executable needs alloca to call xmalloc, because |
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ordinary malloc isn't protected from input signals. On the other |
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hand, the utilities in lib-src need alloca to call malloc; some of |
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them are very simple, and don't have an xmalloc routine. |
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Non-Emacs programs expect this to call xmalloc. |
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Callers below should use malloc. */ |
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# ifndef emacs |
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# define malloc xmalloc |
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# endif |
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extern pointer malloc (); |
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/* Define STACK_DIRECTION if you know the direction of stack |
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growth for your system; otherwise it will be automatically |
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deduced at run-time. |
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STACK_DIRECTION > 0 => grows toward higher addresses |
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STACK_DIRECTION < 0 => grows toward lower addresses |
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STACK_DIRECTION = 0 => direction of growth unknown */ |
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# ifndef STACK_DIRECTION |
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# define STACK_DIRECTION 0 /* Direction unknown. */ |
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# endif |
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# if STACK_DIRECTION != 0 |
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# define STACK_DIR STACK_DIRECTION /* Known at compile-time. */ |
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# else /* STACK_DIRECTION == 0; need run-time code. */ |
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static int stack_dir; /* 1 or -1 once known. */ |
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# define STACK_DIR stack_dir |
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static void |
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find_stack_direction () |
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{ |
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static char *addr = NULL; /* Address of first `dummy', once known. */ |
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auto char dummy; /* To get stack address. */ |
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if (addr == NULL) |
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{ /* Initial entry. */ |
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addr = ADDRESS_FUNCTION (dummy); |
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find_stack_direction (); /* Recurse once. */ |
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} |
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else |
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{ |
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/* Second entry. */ |
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if (ADDRESS_FUNCTION (dummy) > addr) |
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stack_dir = 1; /* Stack grew upward. */ |
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else |
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stack_dir = -1; /* Stack grew downward. */ |
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} |
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} |
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# endif /* STACK_DIRECTION == 0 */ |
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/* An "alloca header" is used to: |
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(a) chain together all alloca'ed blocks; |
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(b) keep track of stack depth. |
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It is very important that sizeof(header) agree with malloc |
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alignment chunk size. The following default should work okay. */ |
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# ifndef ALIGN_SIZE |
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# define ALIGN_SIZE sizeof(double) |
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# endif |
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typedef union hdr |
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{ |
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char align[ALIGN_SIZE]; /* To force sizeof(header). */ |
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struct |
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{ |
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union hdr *next; /* For chaining headers. */ |
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char *deep; /* For stack depth measure. */ |
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} h; |
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} header; |
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static header *last_alloca_header = NULL; /* -> last alloca header. */ |
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/* Return a pointer to at least SIZE bytes of storage, |
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which will be automatically reclaimed upon exit from |
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the procedure that called alloca. Originally, this space |
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was supposed to be taken from the current stack frame of the |
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caller, but that method cannot be made to work for some |
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implementations of C, for example under Gould's UTX/32. */ |
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pointer |
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alloca (size) |
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unsigned size; |
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{ |
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auto char probe; /* Probes stack depth: */ |
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register char *depth = ADDRESS_FUNCTION (probe); |
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# if STACK_DIRECTION == 0 |
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if (STACK_DIR == 0) /* Unknown growth direction. */ |
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find_stack_direction (); |
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# endif |
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/* Reclaim garbage, defined as all alloca'd storage that |
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was allocated from deeper in the stack than currently. */ |
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{ |
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register header *hp; /* Traverses linked list. */ |
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# ifdef emacs |
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BLOCK_INPUT; |
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# endif |
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for (hp = last_alloca_header; hp != NULL;) |
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if ((STACK_DIR > 0 && hp->h.deep > depth) |
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|| (STACK_DIR < 0 && hp->h.deep < depth)) |
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{ |
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register header *np = hp->h.next; |
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free ((pointer) hp); /* Collect garbage. */ |
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hp = np; /* -> next header. */ |
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} |
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else |
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break; /* Rest are not deeper. */ |
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last_alloca_header = hp; /* -> last valid storage. */ |
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# ifdef emacs |
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UNBLOCK_INPUT; |
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# endif |
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} |
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if (size == 0) |
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return NULL; /* No allocation required. */ |
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/* Allocate combined header + user data storage. */ |
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{ |
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register pointer new = malloc (sizeof (header) + size); |
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/* Address of header. */ |
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((header *) new)->h.next = last_alloca_header; |
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((header *) new)->h.deep = depth; |
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last_alloca_header = (header *) new; |
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/* User storage begins just after header. */ |
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return (pointer) ((char *) new + sizeof (header)); |
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} |
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} |
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# if defined (CRAY) && defined (CRAY_STACKSEG_END) |
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# ifdef DEBUG_I00AFUNC |
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# include <stdio.h> |
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# endif |
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# ifndef CRAY_STACK |
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# define CRAY_STACK |
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# ifndef CRAY2 |
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/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ |
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struct stack_control_header |
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{ |
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long shgrow:32; /* Number of times stack has grown. */ |
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long shaseg:32; /* Size of increments to stack. */ |
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long shhwm:32; /* High water mark of stack. */ |
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long shsize:32; /* Current size of stack (all segments). */ |
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}; |
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/* The stack segment linkage control information occurs at |
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the high-address end of a stack segment. (The stack |
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grows from low addresses to high addresses.) The initial |
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part of the stack segment linkage control information is |
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0200 (octal) words. This provides for register storage |
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for the routine which overflows the stack. */ |
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struct stack_segment_linkage |
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{ |
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long ss[0200]; /* 0200 overflow words. */ |
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long sssize:32; /* Number of words in this segment. */ |
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long ssbase:32; /* Offset to stack base. */ |
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long:32; |
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long sspseg:32; /* Offset to linkage control of previous |
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segment of stack. */ |
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long:32; |
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long sstcpt:32; /* Pointer to task common address block. */ |
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long sscsnm; /* Private control structure number for |
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microtasking. */ |
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long ssusr1; /* Reserved for user. */ |
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long ssusr2; /* Reserved for user. */ |
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long sstpid; /* Process ID for pid based multi-tasking. */ |
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long ssgvup; /* Pointer to multitasking thread giveup. */ |
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long sscray[7]; /* Reserved for Cray Research. */ |
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long ssa0; |
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long ssa1; |
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long ssa2; |
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long ssa3; |
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long ssa4; |
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long ssa5; |
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long ssa6; |
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long ssa7; |
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long sss0; |
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long sss1; |
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long sss2; |
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long sss3; |
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long sss4; |
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long sss5; |
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long sss6; |
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long sss7; |
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}; |
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# else /* CRAY2 */ |
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/* The following structure defines the vector of words |
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returned by the STKSTAT library routine. */ |
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struct stk_stat |
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{ |
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long now; /* Current total stack size. */ |
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long maxc; /* Amount of contiguous space which would |
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be required to satisfy the maximum |
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stack demand to date. */ |
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long high_water; /* Stack high-water mark. */ |
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long overflows; /* Number of stack overflow ($STKOFEN) calls. */ |
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long hits; /* Number of internal buffer hits. */ |
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long extends; /* Number of block extensions. */ |
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long stko_mallocs; /* Block allocations by $STKOFEN. */ |
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long underflows; /* Number of stack underflow calls ($STKRETN). */ |
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long stko_free; /* Number of deallocations by $STKRETN. */ |
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long stkm_free; /* Number of deallocations by $STKMRET. */ |
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long segments; /* Current number of stack segments. */ |
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long maxs; /* Maximum number of stack segments so far. */ |
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long pad_size; /* Stack pad size. */ |
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long current_address; /* Current stack segment address. */ |
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long current_size; /* Current stack segment size. This |
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number is actually corrupted by STKSTAT to |
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include the fifteen word trailer area. */ |
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long initial_address; /* Address of initial segment. */ |
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long initial_size; /* Size of initial segment. */ |
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}; |
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/* The following structure describes the data structure which trails |
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any stack segment. I think that the description in 'asdef' is |
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out of date. I only describe the parts that I am sure about. */ |
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struct stk_trailer |
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{ |
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long this_address; /* Address of this block. */ |
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long this_size; /* Size of this block (does not include |
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this trailer). */ |
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long unknown2; |
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long unknown3; |
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long link; /* Address of trailer block of previous |
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segment. */ |
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long unknown5; |
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long unknown6; |
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long unknown7; |
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long unknown8; |
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long unknown9; |
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long unknown10; |
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long unknown11; |
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long unknown12; |
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long unknown13; |
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long unknown14; |
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}; |
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# endif /* CRAY2 */ |
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# endif /* not CRAY_STACK */ |
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# ifdef CRAY2 |
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/* Determine a "stack measure" for an arbitrary ADDRESS. |
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I doubt that "lint" will like this much. */ |
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345 |
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static long |
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i00afunc (long *address) |
347 |
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{ |
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struct stk_stat status; |
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struct stk_trailer *trailer; |
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long *block, size; |
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long result = 0; |
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/* We want to iterate through all of the segments. The first |
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step is to get the stack status structure. We could do this |
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more quickly and more directly, perhaps, by referencing the |
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$LM00 common block, but I know that this works. */ |
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STKSTAT (&status); |
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/* Set up the iteration. */ |
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trailer = (struct stk_trailer *) (status.current_address |
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+ status.current_size |
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- 15); |
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/* There must be at least one stack segment. Therefore it is |
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a fatal error if "trailer" is null. */ |
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369 |
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if (trailer == 0) |
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abort (); |
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/* Discard segments that do not contain our argument address. */ |
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374 |
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while (trailer != 0) |
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{ |
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block = (long *) trailer->this_address; |
377 |
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size = trailer->this_size; |
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if (block == 0 || size == 0) |
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abort (); |
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trailer = (struct stk_trailer *) trailer->link; |
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if ((block <= address) && (address < (block + size))) |
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break; |
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} |
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385 |
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/* Set the result to the offset in this segment and add the sizes |
386 |
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of all predecessor segments. */ |
387 |
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388 |
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result = address - block; |
389 |
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390 |
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if (trailer == 0) |
391 |
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{ |
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return result; |
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} |
394 |
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do |
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{ |
397 |
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if (trailer->this_size <= 0) |
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abort (); |
399 |
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result += trailer->this_size; |
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trailer = (struct stk_trailer *) trailer->link; |
401 |
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} |
402 |
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while (trailer != 0); |
403 |
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404 |
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/* We are done. Note that if you present a bogus address (one |
405 |
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not in any segment), you will get a different number back, formed |
406 |
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from subtracting the address of the first block. This is probably |
407 |
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not what you want. */ |
408 |
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409 |
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|
return (result); |
410 |
|
|
} |
411 |
|
|
|
412 |
|
|
# else /* not CRAY2 */ |
413 |
|
|
/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. |
414 |
|
|
Determine the number of the cell within the stack, |
415 |
|
|
given the address of the cell. The purpose of this |
416 |
|
|
routine is to linearize, in some sense, stack addresses |
417 |
|
|
for alloca. */ |
418 |
|
|
|
419 |
|
|
static long |
420 |
|
|
i00afunc (long address) |
421 |
|
|
{ |
422 |
|
|
long stkl = 0; |
423 |
|
|
|
424 |
|
|
long size, pseg, this_segment, stack; |
425 |
|
|
long result = 0; |
426 |
|
|
|
427 |
|
|
struct stack_segment_linkage *ssptr; |
428 |
|
|
|
429 |
|
|
/* Register B67 contains the address of the end of the |
430 |
|
|
current stack segment. If you (as a subprogram) store |
431 |
|
|
your registers on the stack and find that you are past |
432 |
|
|
the contents of B67, you have overflowed the segment. |
433 |
|
|
|
434 |
|
|
B67 also points to the stack segment linkage control |
435 |
|
|
area, which is what we are really interested in. */ |
436 |
|
|
|
437 |
|
|
stkl = CRAY_STACKSEG_END (); |
438 |
|
|
ssptr = (struct stack_segment_linkage *) stkl; |
439 |
|
|
|
440 |
|
|
/* If one subtracts 'size' from the end of the segment, |
441 |
|
|
one has the address of the first word of the segment. |
442 |
|
|
|
443 |
|
|
If this is not the first segment, 'pseg' will be |
444 |
|
|
nonzero. */ |
445 |
|
|
|
446 |
|
|
pseg = ssptr->sspseg; |
447 |
|
|
size = ssptr->sssize; |
448 |
|
|
|
449 |
|
|
this_segment = stkl - size; |
450 |
|
|
|
451 |
|
|
/* It is possible that calling this routine itself caused |
452 |
|
|
a stack overflow. Discard stack segments which do not |
453 |
|
|
contain the target address. */ |
454 |
|
|
|
455 |
|
|
while (!(this_segment <= address && address <= stkl)) |
456 |
|
|
{ |
457 |
|
|
# ifdef DEBUG_I00AFUNC |
458 |
|
|
fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); |
459 |
|
|
# endif |
460 |
|
|
if (pseg == 0) |
461 |
|
|
break; |
462 |
|
|
stkl = stkl - pseg; |
463 |
|
|
ssptr = (struct stack_segment_linkage *) stkl; |
464 |
|
|
size = ssptr->sssize; |
465 |
|
|
pseg = ssptr->sspseg; |
466 |
|
|
this_segment = stkl - size; |
467 |
|
|
} |
468 |
|
|
|
469 |
|
|
result = address - this_segment; |
470 |
|
|
|
471 |
|
|
/* If you subtract pseg from the current end of the stack, |
472 |
|
|
you get the address of the previous stack segment's end. |
473 |
|
|
This seems a little convoluted to me, but I'll bet you save |
474 |
|
|
a cycle somewhere. */ |
475 |
|
|
|
476 |
|
|
while (pseg != 0) |
477 |
|
|
{ |
478 |
|
|
# ifdef DEBUG_I00AFUNC |
479 |
|
|
fprintf (stderr, "%011o %011o\n", pseg, size); |
480 |
|
|
# endif |
481 |
|
|
stkl = stkl - pseg; |
482 |
|
|
ssptr = (struct stack_segment_linkage *) stkl; |
483 |
|
|
size = ssptr->sssize; |
484 |
|
|
pseg = ssptr->sspseg; |
485 |
|
|
result += size; |
486 |
|
|
} |
487 |
|
|
return (result); |
488 |
|
|
} |
489 |
|
|
|
490 |
|
|
# endif /* not CRAY2 */ |
491 |
|
|
# endif /* CRAY */ |
492 |
|
|
|
493 |
|
|
# endif /* no alloca */ |
494 |
|
|
#endif /* not GCC version 2 */ |