arch/x86/include/asm/orc_lookup.h

   1 /*
   2  * Copyright (C) 2017 Josh Poimboeuf <jpoimboe@redhat.com>
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  16  */
  17 #ifndef _ORC_LOOKUP_H
  18 #define _ORC_LOOKUP_H
  19
  20 /*
  21  * This is a lookup table for speeding up access to the .orc_unwind table.
  22  * Given an input address offset, the corresponding lookup table entry
  23  * specifies a subset of the .orc_unwind table to search.
  24  *
  25  * Each block represents the end of the previous range and the start of the
  26  * next range.  An extra block is added to give the last range an end.
  27  *
  28  * The block size should be a power of 2 to avoid a costly 'div' instruction.
  29  *
  30  * A block size of 256 was chosen because it roughly doubles unwinder
  31  * performance while only adding ~5% to the ORC data footprint.
  32  */
  33 #define LOOKUP_BLOCK_ORDER      8
  34 #define LOOKUP_BLOCK_SIZE       (1 << LOOKUP_BLOCK_ORDER)
  35
  36 #ifndef LINKER_SCRIPT
  37
  38 extern unsigned int orc_lookup[];
  39 extern unsigned int orc_lookup_end[];
  40
  41 #define LOOKUP_START_IP         (unsigned long)_stext
  42 #define LOOKUP_STOP_IP          (unsigned long)_etext
  43
  44 #endif /* LINKER_SCRIPT */
  45
  46 #endif /* _ORC_LOOKUP_H */