1                 : /*
       2                 :  * Copyright (c) 2011 The Native Client Authors. All rights reserved.
       3                 :  * Use of this source code is governed by a BSD-style license that can be
       4                 :  * found in the LICENSE file.
       5                 :  */
       6                 : 
       7                 : #include "native_client/src/trusted/validator/x86/halt_trim.h"
       8                 : 
       9                 : #include <stdio.h>
      10                 : #include "native_client/src/trusted/validator/x86/ncinstbuffer.h"
      11                 : 
      12                 : /* Safety buffer size of halts we must keep, so that we guarantee
      13                 :  * that we don't trim the last legal instruction in the
      14                 :  * code segment. Note: we add 1 to the maximum instruction length just
      15                 :  * to be safe.
      16                 :  */
      17                 : static const NaClMemorySize kMinHaltKeepLength = MAX_INST_LENGTH + 1;
      18                 : 
      19                 : /* x86 HALT opcode */
      20                 : static const uint8_t kNaClHalt = 0xf4;
      21                 : 
      22                 : NaClMemorySize NCHaltTrimSize(uint8_t *mbase, NaClMemorySize sz,
      23               1 :                               uint8_t alignment) {
      24                 :   NaClMemorySize i;
      25                 :   NaClMemorySize num_halts;
      26               1 :   for (i = sz - 1; i > 0; --i) {
      27               1 :     if (kNaClHalt != mbase[i]) break;
      28               1 :   }
      29               1 :   num_halts = sz - (i + 1);
      30               1 :   if (num_halts > kMinHaltKeepLength) {
      31                 :     /* May be able to trim off trailing halts. */
      32                 :     NaClMemorySize new_size;
      33                 :     NaClMemorySize block_overflow;
      34               1 :     new_size = (sz - num_halts) + kMinHaltKeepLength;
      35                 :     /* Round to nearest block alignment. */
      36               1 :     block_overflow = new_size % alignment;
      37               1 :     if (block_overflow) {
      38               1 :       new_size = new_size - block_overflow + alignment;
      39                 :     }
      40                 :     /* Never increase the segment size. */
      41               1 :     if (new_size < sz) {
      42               1 :       return new_size;
      43                 :     }
      44                 :   }
      45                 :   /* No trim performed. */
      46               1 :   return sz;
      47               1 : }