Subversion Repositories openrisc

#include <errno.h>

/*

 * While the heap grows upwards, the stack grows downwards.

 * 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

#ifndef NULL

#define NULL ((void *)0)

#endif

/*

 * sbrk -- changes heap size size. Get nbytes more

 *         RAM. We just increment a pointer in what's

 *         left of memory on the board.

 */

void *sbrk(int nbytes)

{

        /* symbols defined by linker map */

        extern int _end;   // start 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;

        } else {

                errno = ENOMEM;

//              write(1, "Failed to extend heap.", 23);

                return (void *)-1;

        }

}