0,0 → 1,483 |
/* alloca.c -- allocate automatically reclaimed memory |
(Mostly) portable public-domain implementation -- D A Gwyn |
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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. |
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There are some preprocessor constants that can |
be defined when compiling for your specific system, for |
improved efficiency; however, the defaults should be okay. |
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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. |
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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. */ |
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/* |
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@deftypefn Replacement void* alloca (size_t @var{size}) |
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This function allocates memory which will be automatically reclaimed |
after the procedure exits. The @libib{} implementation does not free |
the memory immediately but will do so eventually during subsequent |
calls to this function. Memory is allocated using @code{xmalloc} under |
normal circumstances. |
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The header file @file{alloca-conf.h} can be used in conjunction with the |
GNU Autoconf test @code{AC_FUNC_ALLOCA} to test for and properly make |
available this function. The @code{AC_FUNC_ALLOCA} test requires that |
client code use a block of preprocessor code to be safe (see the Autoconf |
manual for more); this header incorporates that logic and more, including |
the possibility of a GCC built-in function. |
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@end deftypefn |
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*/ |
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#ifdef HAVE_CONFIG_H |
#include <config.h> |
#endif |
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#include <libiberty.h> |
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#ifdef HAVE_STRING_H |
#include <string.h> |
#endif |
#ifdef HAVE_STDLIB_H |
#include <stdlib.h> |
#endif |
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/* These variables are used by the ASTRDUP implementation that relies |
on C_alloca. */ |
#ifdef __cplusplus |
extern "C" { |
#endif /* __cplusplus */ |
const char *libiberty_optr; |
char *libiberty_nptr; |
unsigned long libiberty_len; |
#ifdef __cplusplus |
} |
#endif /* __cplusplus */ |
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/* If your stack is a linked list of frames, you have to |
provide an "address metric" ADDRESS_FUNCTION macro. */ |
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#if defined (CRAY) && defined (CRAY_STACKSEG_END) |
static long i00afunc (); |
#define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) |
#else |
#define ADDRESS_FUNCTION(arg) &(arg) |
#endif |
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#ifndef NULL |
#define NULL 0 |
#endif |
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/* Define STACK_DIRECTION if you know the direction of stack |
growth for your system; otherwise it will be automatically |
deduced at run-time. |
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STACK_DIRECTION > 0 => grows toward higher addresses |
STACK_DIRECTION < 0 => grows toward lower addresses |
STACK_DIRECTION = 0 => direction of growth unknown */ |
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#ifndef STACK_DIRECTION |
#define STACK_DIRECTION 0 /* Direction unknown. */ |
#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. */ |
#define STACK_DIR stack_dir |
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static void |
find_stack_direction (void) |
{ |
static char *addr = NULL; /* Address of first `dummy', once known. */ |
auto char dummy; /* To get stack address. */ |
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if (addr == NULL) |
{ /* Initial entry. */ |
addr = ADDRESS_FUNCTION (dummy); |
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find_stack_direction (); /* Recurse once. */ |
} |
else |
{ |
/* Second entry. */ |
if (ADDRESS_FUNCTION (dummy) > addr) |
stack_dir = 1; /* Stack grew upward. */ |
else |
stack_dir = -1; /* Stack grew downward. */ |
} |
} |
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#endif /* STACK_DIRECTION == 0 */ |
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/* An "alloca header" is used to: |
(a) chain together all alloca'ed blocks; |
(b) keep track of stack depth. |
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It is very important that sizeof(header) agree with malloc |
alignment chunk size. The following default should work okay. */ |
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#ifndef ALIGN_SIZE |
#define ALIGN_SIZE sizeof(double) |
#endif |
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typedef union hdr |
{ |
char align[ALIGN_SIZE]; /* To force sizeof(header). */ |
struct |
{ |
union hdr *next; /* For chaining headers. */ |
char *deep; /* For stack depth measure. */ |
} h; |
} 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, |
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. */ |
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/* @undocumented C_alloca */ |
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PTR |
C_alloca (size_t size) |
{ |
auto char probe; /* Probes stack depth: */ |
register char *depth = ADDRESS_FUNCTION (probe); |
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#if STACK_DIRECTION == 0 |
if (STACK_DIR == 0) /* Unknown growth direction. */ |
find_stack_direction (); |
#endif |
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/* Reclaim garbage, defined as all alloca'd storage that |
was allocated from deeper in the stack than currently. */ |
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{ |
register header *hp; /* Traverses linked list. */ |
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for (hp = last_alloca_header; hp != NULL;) |
if ((STACK_DIR > 0 && hp->h.deep > depth) |
|| (STACK_DIR < 0 && hp->h.deep < depth)) |
{ |
register header *np = hp->h.next; |
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free ((PTR) hp); /* Collect garbage. */ |
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hp = np; /* -> next header. */ |
} |
else |
break; /* Rest are not deeper. */ |
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last_alloca_header = hp; /* -> last valid storage. */ |
} |
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if (size == 0) |
return NULL; /* No allocation required. */ |
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/* Allocate combined header + user data storage. */ |
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{ |
register void *new_storage = XNEWVEC (char, sizeof (header) + size); |
/* Address of header. */ |
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if (new_storage == 0) |
abort(); |
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((header *) new_storage)->h.next = last_alloca_header; |
((header *) new_storage)->h.deep = depth; |
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last_alloca_header = (header *) new_storage; |
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/* User storage begins just after header. */ |
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return (PTR) ((char *) new_storage + sizeof (header)); |
} |
} |
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#if defined (CRAY) && defined (CRAY_STACKSEG_END) |
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#ifdef DEBUG_I00AFUNC |
#include <stdio.h> |
#endif |
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#ifndef CRAY_STACK |
#define CRAY_STACK |
#ifndef CRAY2 |
/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ |
struct stack_control_header |
{ |
long shgrow:32; /* Number of times stack has grown. */ |
long shaseg:32; /* Size of increments to stack. */ |
long shhwm:32; /* High water mark of stack. */ |
long shsize:32; /* Current size of stack (all segments). */ |
}; |
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/* 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. */ |
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struct stack_segment_linkage |
{ |
long ss[0200]; /* 0200 overflow words. */ |
long sssize:32; /* Number of words in this segment. */ |
long ssbase:32; /* Offset to stack base. */ |
long:32; |
long sspseg:32; /* Offset to linkage control of previous |
segment of stack. */ |
long:32; |
long sstcpt:32; /* Pointer to task common address block. */ |
long sscsnm; /* Private control structure number for |
microtasking. */ |
long ssusr1; /* Reserved for user. */ |
long ssusr2; /* Reserved for user. */ |
long sstpid; /* Process ID for pid based multi-tasking. */ |
long ssgvup; /* Pointer to multitasking thread giveup. */ |
long sscray[7]; /* Reserved for Cray Research. */ |
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; |
}; |
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#else /* CRAY2 */ |
/* The following structure defines the vector of words |
returned by the STKSTAT library routine. */ |
struct stk_stat |
{ |
long now; /* Current total stack size. */ |
long maxc; /* Amount of contiguous space which would |
be required to satisfy the maximum |
stack demand to date. */ |
long high_water; /* Stack high-water mark. */ |
long overflows; /* Number of stack overflow ($STKOFEN) calls. */ |
long hits; /* Number of internal buffer hits. */ |
long extends; /* Number of block extensions. */ |
long stko_mallocs; /* Block allocations by $STKOFEN. */ |
long underflows; /* Number of stack underflow calls ($STKRETN). */ |
long stko_free; /* Number of deallocations by $STKRETN. */ |
long stkm_free; /* Number of deallocations by $STKMRET. */ |
long segments; /* Current number of stack segments. */ |
long maxs; /* Maximum number of stack segments so far. */ |
long pad_size; /* Stack pad size. */ |
long current_address; /* Current stack segment address. */ |
long current_size; /* Current stack segment size. This |
number is actually corrupted by STKSTAT to |
include the fifteen word trailer area. */ |
long initial_address; /* Address of initial segment. */ |
long initial_size; /* Size of initial segment. */ |
}; |
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/* 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. */ |
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struct stk_trailer |
{ |
long this_address; /* Address of this block. */ |
long this_size; /* Size of this block (does not include |
this trailer). */ |
long unknown2; |
long unknown3; |
long link; /* Address of trailer block of previous |
segment. */ |
long unknown5; |
long unknown6; |
long unknown7; |
long unknown8; |
long unknown9; |
long unknown10; |
long unknown11; |
long unknown12; |
long unknown13; |
long unknown14; |
}; |
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#endif /* CRAY2 */ |
#endif /* not CRAY_STACK */ |
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#ifdef CRAY2 |
/* Determine a "stack measure" for an arbitrary ADDRESS. |
I doubt that "lint" will like this much. */ |
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static long |
i00afunc (long *address) |
{ |
struct stk_stat status; |
struct stk_trailer *trailer; |
long *block, size; |
long result = 0; |
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/* 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. */ |
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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 |
+ status.current_size |
- 15); |
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/* There must be at least one stack segment. Therefore it is |
a fatal error if "trailer" is null. */ |
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if (trailer == 0) |
abort (); |
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/* Discard segments that do not contain our argument address. */ |
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while (trailer != 0) |
{ |
block = (long *) trailer->this_address; |
size = trailer->this_size; |
if (block == 0 || size == 0) |
abort (); |
trailer = (struct stk_trailer *) trailer->link; |
if ((block <= address) && (address < (block + size))) |
break; |
} |
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/* Set the result to the offset in this segment and add the sizes |
of all predecessor segments. */ |
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result = address - block; |
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if (trailer == 0) |
{ |
return result; |
} |
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do |
{ |
if (trailer->this_size <= 0) |
abort (); |
result += trailer->this_size; |
trailer = (struct stk_trailer *) trailer->link; |
} |
while (trailer != 0); |
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/* 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. */ |
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return (result); |
} |
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#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. */ |
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static long |
i00afunc (long address) |
{ |
long stkl = 0; |
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long size, pseg, this_segment, stack; |
long result = 0; |
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struct stack_segment_linkage *ssptr; |
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/* 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. |
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B67 also points to the stack segment linkage control |
area, which is what we are really interested in. */ |
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stkl = CRAY_STACKSEG_END (); |
ssptr = (struct stack_segment_linkage *) stkl; |
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/* If one subtracts 'size' from the end of the segment, |
one has the address of the first word of the segment. |
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If this is not the first segment, 'pseg' will be |
nonzero. */ |
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pseg = ssptr->sspseg; |
size = ssptr->sssize; |
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this_segment = stkl - size; |
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/* It is possible that calling this routine itself caused |
a stack overflow. Discard stack segments which do not |
contain the target address. */ |
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while (!(this_segment <= address && address <= stkl)) |
{ |
#ifdef DEBUG_I00AFUNC |
fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); |
#endif |
if (pseg == 0) |
break; |
stkl = stkl - pseg; |
ssptr = (struct stack_segment_linkage *) stkl; |
size = ssptr->sssize; |
pseg = ssptr->sspseg; |
this_segment = stkl - size; |
} |
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result = address - this_segment; |
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/* 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. */ |
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while (pseg != 0) |
{ |
#ifdef DEBUG_I00AFUNC |
fprintf (stderr, "%011o %011o\n", pseg, size); |
#endif |
stkl = stkl - pseg; |
ssptr = (struct stack_segment_linkage *) stkl; |
size = ssptr->sssize; |
pseg = ssptr->sspseg; |
result += size; |
} |
return (result); |
} |
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#endif /* not CRAY2 */ |
#endif /* CRAY */ |