newlib/libc/sys/mmixware/sbrk.c

   1 /* sbrk for MMIXware.
   2
   3    Copyright (C) 2001, 2012, 2023 Hans-Peter Nilsson
   4
   5    Permission to use, copy, modify, and distribute this software is
   6    freely granted, provided that the above copyright notice, this notice
   7    and the following disclaimer are preserved with no changes.
   8
   9    THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
  10    IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  11    WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  12    PURPOSE.  */
  13
  14 #include <_ansi.h>
  15 #include <sys/types.h>
  16 #include <sys/stat.h>
  17 #include "sys/syscall.h"
  18
  19 extern char *_Sbrk_high;
  20
  21 /* When the program is loaded, the first location in Pool_Segment holds
  22    the first available octabyte in the memory pool (a.k.a. the heap);
  23    somewhere after the command-line parameters.  We don't have to
  24    initialize that location, we can just use it straight up as a pointer;
  25    just point the symbol there.
  26
  27    This file will be compiled with -no-builtin-syms, so we need to define
  28    Pool_Segment and any other symbols that would be predefined in mmixal.  */
  29
  30 __asm__ (" .global _Sbrk_high\n"
  31          "_Sbrk_high    IS      Pool_Segment\n"
  32          "Pool_Segment  IS      0x40<<56");
  33
  34 void *
  35 _sbrk (ptrdiff_t incr)
  36 {
  37   void *prev_heap_end;
  38
  39   prev_heap_end = _Sbrk_high;
  40
  41   /* A simulator that requires explicit memory allocation is expected
  42      to hook that to the PRELD data prefetch insn, which is otherwise
  43      typically a nop.  */
  44   if ((long) incr > 0)
  45     {
  46       size_t n = incr;
  47       char *p = prev_heap_end;
  48 #define A(N) __asm__ ("preld " #N ",%0,0" : : "r" (p))
  49 #define PRELDOWNTO(N) while (n >= N + 1) { A(N); n -= N + 1; p += N + 1; }
  50
  51       PRELDOWNTO (255);
  52       PRELDOWNTO (31);
  53       PRELDOWNTO (3);
  54       PRELDOWNTO (0);
  55     }
  56
  57   _Sbrk_high += incr;
  58   return prev_heap_end;
  59 }