/* sbrk.c. Implementation of the _sbrk syscall for newlib
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/* sbrk.c. Implementation of the _sbrk syscall for newlib
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Copyright (C) 2004, Jacob Bower
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Copyright (C) 2004, Jacob Bower
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Copyright (C) 2010, Embecosm Limited <info@embecosm.com>
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Copyright (C) 2010, Embecosm Limited <info@embecosm.com>
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Contributor Jeremy Bennett <jeremy.bennett@embecosm.com>
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Contributor Jeremy Bennett <jeremy.bennett@embecosm.com>
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This file is part of Newlib.
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This file is part of Newlib.
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The original work by Jacob Bower is provided as-is without any kind of
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The original work by Jacob Bower is provided as-is without any kind of
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warranty. Use it at your own risk!
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warranty. Use it at your own risk!
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All subsequent work is bound by version 3 of the GPL as follows.
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All subsequent work is bound by version 3 of the GPL as follows.
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This program is free software; you can redistribute it and/or modify it
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This program is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the Free
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under the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your option)
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Software Foundation; either version 3 of the License, or (at your option)
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any later version.
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any later version.
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This program is distributed in the hope that it will be useful, but WITHOUT
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This program is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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more details.
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You should have received a copy of the GNU General Public License along
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You should have received a copy of the GNU General Public License along
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with this program. If not, see <http:#www.gnu.org/licenses/>. */
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with this program. If not, see <http:#www.gnu.org/licenses/>. */
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/* -------------------------------------------------------------------------- */
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/* -------------------------------------------------------------------------- */
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/* This program is commented throughout in a fashion suitable for processing
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/* This program is commented throughout in a fashion suitable for processing
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with Doxygen. */
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with Doxygen. */
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/* -------------------------------------------------------------------------- */
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/* -------------------------------------------------------------------------- */
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#include <errno.h>
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#include <errno.h>
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#undef errno
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#undef errno
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extern int errno;
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extern int errno;
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#define STACK_BUFFER 65536 /*!< Reserved stack space in bytes. */
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#define STACK_BUFFER 65536 /*!< Reserved stack space in bytes. */
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/* -------------------------------------------------------------------------- */
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/* -------------------------------------------------------------------------- */
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/*!Extend the heap
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/*!Extend the heap
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We just increment a pointer in what's left of memory on the board.
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We just increment a pointer in what's left of memory on the board.
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While the heap grows upwards, the stack grows downwards. Eventually these
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While the heap grows upwards, the stack grows downwards. Eventually these
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two things may colide and sbrk() won't even be able to return properly.
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two things may colide and sbrk() won't even be able to return properly.
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To mitigate this we reserve upto STACK_BUFFER _words_ at the top of memory.
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To mitigate this we reserve upto STACK_BUFFER _words_ at the top of memory.
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Note this doesn't actually solve the problem, it just provides an error
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Note this doesn't actually solve the problem, it just provides an error
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margin. The real solution is to use an OS with a proper virtual memory
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margin. The real solution is to use an OS with a proper virtual memory
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manager.
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manager.
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Remember that this function is *not* reentrant, so no static state should
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Remember that this function is *not* reentrant, so no static state should
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be held.
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be held.
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@todo We break this rule with heap_ptr. This needs to be clean, so that a
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@todo We break this rule with heap_ptr. This needs to be clean, so that a
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re-entrant call to sbrk (e.g. in an ISR) is certain to work.
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re-entrant call to sbrk (e.g. in an ISR) is certain to work.
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@param[in] nbytes The number of bytes to be allocated.
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@param[in] nbytes The number of bytes to be allocated.
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@return The previous heap end on success, -1 on failure with an error
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@return The previous heap end on success, -1 on failure with an error
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code in errno. */
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code in errno. */
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/* -------------------------------------------------------------------------- */
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/* -------------------------------------------------------------------------- */
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void *
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void *
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_sbrk (int nbytes)
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_sbrk (int nbytes)
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{
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{
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/* Symbol defined by linker map */
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/* Symbol defined by linker map */
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extern int end; /* start of free memory (as symbol) */
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extern int end; /* start of free memory (as symbol) */
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/* Value set by crt0.S */
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/* Value set by crt0.S */
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extern void *stack; /* end of free memory */
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extern void *stack; /* end of free memory */
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/* The statically held previous end of the heap, with its initialization. */
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/* The statically held previous end of the heap, with its initialization. */
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static void *heap_ptr = (void *)&end; /* Previous end */
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static void *heap_ptr = (void *)&end; /* Previous end */
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if ((stack - (heap_ptr + nbytes)) > STACK_BUFFER )
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if ((stack - (heap_ptr + nbytes)) > STACK_BUFFER )
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{
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{
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void *base = heap_ptr;
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void *base = heap_ptr;
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heap_ptr += nbytes;
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heap_ptr += nbytes;
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return base;
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return base;
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}
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}
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else
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else
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{
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{
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errno = ENOMEM;
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errno = ENOMEM;
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return (void *) -1;
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return (void *) -1;
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}
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}
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} /* _sbrk () */
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} /* _sbrk () */
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