70696c0161
we had incorrect usage of setstackmark()/popstackmark()
There was an ancient idiom (imported from CSRG in 1993) where code
can do:
setstackmark(&smark); loop until whatever condition {
/* do lots of code */ popstackmark(&smark);
} popstackmark(&smark);
The 1st (inner) popstackmark() resets the stack, conserving memory,
The 2nd one is needed just in case the "whatever condition" was never
true, and the first one was never executed.
This is (was) safe as all popstackmark() did was reset the stack.
That could be done over and over again with no harm.
That is, until 2000 when a fix from FreeBSD for another problem was
imported. That connected all the stack marks as a list (so they can be
located). That caused the problem, as the idiom was not changed, now
there is this list of marks, and popstackmark() was removing an entry.
It rarely (never?) caused any problems as the idiom was rarely used
(the shell used to do loops like above, mostly, without the inner
popstackmark()). Further, the stack mark list is only ever used when
a memory block is realloc'd.
That is, until last weekend - with the recent set of changes.
Part of that copied code from FreeBSD introduced the idiom above
into more functions - functions used much more, and with a greater
possibility of stack marks being set on blocks that are realloc'd
and so cause the problem. In the FreeBSD code, they changed the idiom,
and always do a setstackmark() immediately after the inner popstackmark().
But not for reasons related to a list of stack marks, as in the
intervening period, FreeBSD deleted that, but for another reason.
We do not have their issue, and I did not believe that their
updated idiom was needed (I did some analysis of exactly this issue -
just missed the important part!), and just continued using the old one.
Hence Patrick's core dump....
The solution used here is to split popstackmark() into 2 halves,
popstackmark() continues to do what it has (recently) done,
but is now implemented as a call of (a new func) rststackmark()
which does all the original work of popstackmark - but not removing
the entry from the stack mark list (which remains in popstackmark()).
Then in the idiom above, the inner popstackmark() turns into a call of
rststackmark() so the stack is reset, but the stack mark list is
unchanged. Tail recursion elimination makes this essentially free.
335 lines
8.4 KiB
C
335 lines
8.4 KiB
C
/* $NetBSD: memalloc.c,v 1.32 2018/08/22 20:08:54 kre Exp $ */
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/*-
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* Copyright (c) 1991, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Kenneth Almquist.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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#ifndef lint
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#if 0
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static char sccsid[] = "@(#)memalloc.c 8.3 (Berkeley) 5/4/95";
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#else
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__RCSID("$NetBSD: memalloc.c,v 1.32 2018/08/22 20:08:54 kre Exp $");
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#endif
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#endif /* not lint */
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#include <stdlib.h>
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#include <unistd.h>
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#include "shell.h"
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#include "output.h"
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#include "memalloc.h"
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#include "error.h"
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#include "machdep.h"
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#include "mystring.h"
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/*
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* Like malloc, but returns an error when out of space.
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*/
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pointer
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ckmalloc(size_t nbytes)
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{
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pointer p;
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p = malloc(nbytes);
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if (p == NULL)
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error("Out of space");
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return p;
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}
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/*
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* Same for realloc.
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*/
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pointer
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ckrealloc(pointer p, int nbytes)
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{
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p = realloc(p, nbytes);
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if (p == NULL)
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error("Out of space");
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return p;
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}
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/*
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* Make a copy of a string in safe storage.
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*/
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char *
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savestr(const char *s)
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{
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char *p;
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p = ckmalloc(strlen(s) + 1);
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scopy(s, p);
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return p;
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}
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/*
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* Parse trees for commands are allocated in lifo order, so we use a stack
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* to make this more efficient, and also to avoid all sorts of exception
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* handling code to handle interrupts in the middle of a parse.
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*
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* The size 504 was chosen because the Ultrix malloc handles that size
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* well.
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*/
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#define MINSIZE 504 /* minimum size of a block */
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struct stack_block {
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struct stack_block *prev;
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char space[MINSIZE];
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};
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struct stack_block stackbase;
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struct stack_block *stackp = &stackbase;
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struct stackmark *markp;
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char *stacknxt = stackbase.space;
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int stacknleft = MINSIZE;
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int sstrnleft;
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int herefd = -1;
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pointer
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stalloc(int nbytes)
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{
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char *p;
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nbytes = SHELL_ALIGN(nbytes);
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if (nbytes > stacknleft) {
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int blocksize;
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struct stack_block *sp;
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blocksize = nbytes;
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if (blocksize < MINSIZE)
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blocksize = MINSIZE;
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INTOFF;
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sp = ckmalloc(sizeof(struct stack_block) - MINSIZE + blocksize);
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sp->prev = stackp;
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stacknxt = sp->space;
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stacknleft = blocksize;
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stackp = sp;
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INTON;
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}
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p = stacknxt;
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stacknxt += nbytes;
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stacknleft -= nbytes;
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return p;
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}
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void
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stunalloc(pointer p)
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{
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if (p == NULL) { /*DEBUG */
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write(2, "stunalloc\n", 10);
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abort();
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}
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stacknleft += stacknxt - (char *)p;
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stacknxt = p;
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}
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/* save the current status of the sh stack */
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void
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setstackmark(struct stackmark *mark)
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{
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mark->stackp = stackp;
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mark->stacknxt = stacknxt;
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mark->stacknleft = stacknleft;
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mark->sstrnleft = sstrnleft;
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mark->marknext = markp;
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markp = mark;
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}
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/* reset the stack mark, and remove it from the list of marks */
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void
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popstackmark(struct stackmark *mark)
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{
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markp = mark->marknext; /* delete mark from the list */
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rststackmark(mark); /* and reset stack */
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}
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/* reset the shell stack to its state recorded in the stack mark */
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void
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rststackmark(struct stackmark *mark)
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{
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struct stack_block *sp;
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INTOFF;
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while (stackp != mark->stackp) {
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/* delete any recently allocated mem blocks */
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sp = stackp;
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stackp = sp->prev;
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ckfree(sp);
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}
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stacknxt = mark->stacknxt;
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stacknleft = mark->stacknleft;
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sstrnleft = mark->sstrnleft;
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INTON;
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}
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/*
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* When the parser reads in a string, it wants to stick the string on the
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* stack and only adjust the stack pointer when it knows how big the
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* string is. Stackblock (defined in stack.h) returns a pointer to a block
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* of space on top of the stack and stackblocklen returns the length of
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* this block. Growstackblock will grow this space by at least one byte,
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* possibly moving it (like realloc). Grabstackblock actually allocates the
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* part of the block that has been used.
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*/
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void
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growstackblock(void)
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{
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int newlen = SHELL_ALIGN(stacknleft * 2 + 100);
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INTOFF;
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if (stacknxt == stackp->space && stackp != &stackbase) {
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struct stack_block *oldstackp;
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struct stackmark *xmark;
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struct stack_block *sp;
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oldstackp = stackp;
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sp = stackp;
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stackp = sp->prev;
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sp = ckrealloc((pointer)sp,
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sizeof(struct stack_block) - MINSIZE + newlen);
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sp->prev = stackp;
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stackp = sp;
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stacknxt = sp->space;
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sstrnleft += newlen - stacknleft;
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stacknleft = newlen;
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/*
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* Stack marks pointing to the start of the old block
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* must be relocated to point to the new block
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*/
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xmark = markp;
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while (xmark != NULL && xmark->stackp == oldstackp) {
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xmark->stackp = stackp;
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xmark->stacknxt = stacknxt;
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xmark->sstrnleft += stacknleft - xmark->stacknleft;
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xmark->stacknleft = stacknleft;
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xmark = xmark->marknext;
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}
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} else {
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char *oldspace = stacknxt;
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int oldlen = stacknleft;
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char *p = stalloc(newlen);
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(void)memcpy(p, oldspace, oldlen);
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stacknxt = p; /* free the space */
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stacknleft += newlen; /* we just allocated */
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}
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INTON;
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}
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void
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grabstackblock(int len)
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{
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len = SHELL_ALIGN(len);
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stacknxt += len;
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stacknleft -= len;
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}
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/*
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* The following routines are somewhat easier to use than the above.
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* The user declares a variable of type STACKSTR, which may be declared
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* to be a register. The macro STARTSTACKSTR initializes things. Then
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* the user uses the macro STPUTC to add characters to the string. In
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* effect, STPUTC(c, p) is the same as *p++ = c except that the stack is
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* grown as necessary. When the user is done, she can just leave the
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* string there and refer to it using stackblock(). Or she can allocate
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* the space for it using grabstackstr(). If it is necessary to allow
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* someone else to use the stack temporarily and then continue to grow
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* the string, the user should use grabstack to allocate the space, and
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* then call ungrabstr(p) to return to the previous mode of operation.
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*
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* USTPUTC is like STPUTC except that it doesn't check for overflow.
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* CHECKSTACKSPACE can be called before USTPUTC to ensure that there
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* is space for at least one character.
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*/
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char *
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growstackstr(void)
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{
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int len = stackblocksize();
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if (herefd >= 0 && len >= 1024) {
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xwrite(herefd, stackblock(), len);
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sstrnleft = len - 1;
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return stackblock();
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}
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growstackblock();
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sstrnleft = stackblocksize() - len - 1;
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return stackblock() + len;
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}
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/*
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* Called from CHECKSTRSPACE.
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*/
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char *
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makestrspace(void)
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{
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int len = stackblocksize() - sstrnleft;
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growstackblock();
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sstrnleft = stackblocksize() - len;
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return stackblock() + len;
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}
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/*
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* Note that this only works to release stack space for reuse
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* if nothing else has allocated space on the stack since the grabstackstr()
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*
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* "s" is the start of the area to be released, and "p" represents the end
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* of the string we have stored beyond there and are now releasing.
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* (ie: "p" should be the same as in the call to grabstackstr()).
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*
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* stunalloc(s) and ungrabstackstr(s, p) are almost interchangable after
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* a grabstackstr(), however the latter also returns string space so we
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* can just continue with STPUTC() etc without needing a new STARTSTACKSTR(s)
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*/
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void
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ungrabstackstr(char *s, char *p)
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{
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#ifdef DEBUG
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if (s < stacknxt || stacknxt + stacknleft < s)
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abort();
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#endif
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stacknleft += stacknxt - s;
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stacknxt = s;
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sstrnleft = stacknleft - (p - s);
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}
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