| Line 1... |
Line 1... |
|
/* sbrk.c. Implementation of the _sbrk syscall for newlib
|
|
|
|
Copyright (C) 2004, Jacob Bower
|
|
Copyright (C) 2010, Embecosm Limited <info@embecosm.com>
|
|
|
|
Contributor Jeremy Bennett <jeremy.bennett@embecosm.com>
|
|
|
|
This file is part of Newlib.
|
|
|
|
The original work by Jacob Bower is provided as-is without any kind of
|
|
warranty. Use it at your own risk!
|
|
|
|
All subsequent work is bound by version 3 of the GPL as follows.
|
|
|
|
This program is free software; you can redistribute it and/or modify it
|
|
under the terms of the GNU General Public License as published by the Free
|
|
Software Foundation; either version 3 of the License, or (at your option)
|
|
any later version.
|
|
|
|
This program is distributed in the hope that it will be useful, but WITHOUT
|
|
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
|
|
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
|
|
more details.
|
|
|
|
You should have received a copy of the GNU General Public License along
|
|
with this program. If not, see <http:#www.gnu.org/licenses/>. */
|
|
/* -------------------------------------------------------------------------- */
|
|
/* This program is commented throughout in a fashion suitable for processing
|
|
with Doxygen. */
|
|
/* -------------------------------------------------------------------------- */
|
|
|
#include <errno.h>
|
#include <errno.h>
|
|
|
/*
|
/*! Reserved stack space inbytes. */
|
* While the heap grows upwards, the stack grows downwards.
|
#define STACK_BUFFER 65536
|
* Evnetually these two things may colide and sbrk()
|
|
* won't even be able to return properly. To mitigate this
|
|
* we reserve upto STACK_BUFFER _words_ at the top of memory.
|
|
* Note this doesn't actually solve the problem, it just
|
|
* provides an error margin. The real solution is to use
|
|
* an OS with a proper virtual memory manager.
|
|
*/
|
|
#define STACK_BUFFER 16384
|
|
|
|
|
/*! Define NULL if not yet defined. */
|
#ifndef NULL
|
#ifndef NULL
|
#define NULL ((void *)0)
|
#define NULL ((void *)0)
|
#endif
|
#endif
|
|
|
|
|
/*
|
/* -------------------------------------------------------------------------- */
|
* sbrk -- changes heap size size. Get nbytes more
|
/*!Extend the heap
|
* RAM. We just increment a pointer in what's
|
|
* left of memory on the board.
|
We just increment a pointer in what's left of memory on the board.
|
*/
|
|
void *sbrk(int nbytes)
|
While the heap grows upwards, the stack grows downwards. Eventually these
|
|
two things may colide and sbrk() won't even be able to return properly.
|
|
|
|
To mitigate this we reserve upto STACK_BUFFER _words_ at the top of memory.
|
|
Note this doesn't actually solve the problem, it just provides an error
|
|
margin. The real solution is to use an OS with a proper virtual memory
|
|
manager.
|
|
|
|
Remember that this function is *not* reentrant, so no static state should
|
|
be held.
|
|
|
|
@todo We break this rule with heap_ptr. This needs to be clean, so that a
|
|
re-entrant call to sbrk (e.g. in an ISR) is certain to work.
|
|
|
|
@param[in] nbytes The number of bytes to be allocated.
|
|
|
|
@return The previous heap end on success, -1 on failure with an error
|
|
code in errno. */
|
|
/* -------------------------------------------------------------------------- */
|
|
void *
|
|
_sbrk (int nbytes)
|
{
|
{
|
/* symbols defined by linker map */
|
/* Symbols defined by linker map */
|
extern int _end; // start of free memory
|
extern int end; /* start of free memory */
|
extern int _stack; // end of free memory
|
extern int stack; /* end of free memory */
|
|
|
static unsigned long *heap_ptr = NULL;
|
|
void *base;
|
|
int nwords = (nbytes + 3) / 4;
|
|
|
|
if (heap_ptr == NULL)
|
|
heap_ptr = (unsigned long *)&_end;
|
|
|
|
if ( ((unsigned long *)&_stack - (heap_ptr + nwords)) > STACK_BUFFER ) {
|
|
base = heap_ptr;
|
|
heap_ptr += nwords;
|
|
|
|
return (void *)base;
|
/* The statically held previous end of the stack, with its initialization. */
|
} else {
|
static void *heap_ptr = (void *)&end; /* Previous end */
|
errno = ENOMEM;
|
|
// write(1, "Failed to extend heap.", 23);
|
|
|
|
return (void *)-1;
|
if (((void *) &stack - (heap_ptr + nbytes)) > STACK_BUFFER )
|
|
{
|
|
void * base = heap_ptr;
|
|
heap_ptr += nbytes;
|
|
|
|
return base;
|
}
|
}
|
|
else
|
|
{
|
|
errno = ENOMEM;
|
|
return (void *) -1;
|
}
|
}
|
|
} /* _sbrk () */
|
|
|
No newline at end of file
|
No newline at end of file
|
