libgo/runtime/go-memclr.c

   1 /* go-memclr.c -- clear a memory buffer
   2
   3    Copyright 2016 The Go Authors. All rights reserved.
   4    Use of this source code is governed by a BSD-style
   5    license that can be found in the LICENSE file.  */
   6
   7 #include "runtime.h"
   8
   9 void memclrNoHeapPointers(void *, uintptr)
  10   __asm__ (GOSYM_PREFIX "runtime.memclrNoHeapPointers")
  11   __attribute__ ((no_split_stack));
  12
  13 void
  14 memclrNoHeapPointers (void *p1, uintptr len)
  15 {
  16
  17 #if !defined(__PPC64__)
  18   __builtin_memset(p1, 0, len);
  19 #else
  20   int64 rem,drem,i;
  21   uint64 offset;
  22   volatile uint64 *vp;
  23
  24   if (len == 0) {
  25     return;
  26   }
  27   rem = len;
  28
  29   offset = (uint64)p1 % 8;
  30   // This memset is OK since it can't contain
  31   // an 8 byte aligned pointer.
  32   if ((rem < 8) || (offset > 0 && offset+rem <= 16)) {
  33     __builtin_memset(p1, 0, rem);
  34     return;
  35   }
  36   // Move initial bytes to get to 8 byte boundary
  37   if (offset > 0) {
  38     __builtin_memset(p1, 0, 8-offset);
  39     p1 = (void*)((char*)p1+8-offset);
  40     rem -= 8-offset;
  41   }
  42
  43   // If at least 8 bytes left, clear
  44   drem = rem>>3;
  45
  46   vp = (volatile uint64*)(p1);
  47   // Without the use of volatile here, the compiler
  48   // might convert the loop into a memset.
  49   for (i=0; i<drem; i++) {
  50     *vp = 0;
  51     vp++;
  52     rem -= 8;
  53   }
  54   p1 = (void*)((char*)p1 + 8*drem);
  55   // Clear any remaining
  56   if (rem > 0) {
  57     __builtin_memset (p1, 0, rem);
  58   }
  59 #endif
  60 }