1  /* Restartable Sequences Linux s390 architecture header.
       2     Copyright (C) 2021-2023 Free Software Foundation, Inc.
       3  
       4     The GNU C Library is free software; you can redistribute it and/or
       5     modify it under the terms of the GNU Lesser General Public
       6     License as published by the Free Software Foundation; either
       7     version 2.1 of the License, or (at your option) any later version.
       8  
       9     The GNU C Library 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 GNU
      12     Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public
      15     License along with the GNU C Library; if not, see
      16     <https://www.gnu.org/licenses/>.  */
      17  
      18  #ifndef _SYS_RSEQ_H
      19  # error "Never use <bits/rseq.h> directly; include <sys/rseq.h> instead."
      20  #endif
      21  
      22  /* RSEQ_SIG is a signature required before each abort handler code.
      23  
      24     It is a 32-bit value that maps to actual architecture code compiled
      25     into applications and libraries.  It needs to be defined for each
      26     architecture.  When choosing this value, it needs to be taken into
      27     account that generating invalid instructions may have ill effects on
      28     tools like objdump, and may also have impact on the CPU speculative
      29     execution efficiency in some cases.
      30  
      31     RSEQ_SIG uses the trap4 instruction.  As Linux does not make use of the
      32     access-register mode nor the linkage stack this instruction will always
      33     cause a special-operation exception (the trap-enabled bit in the DUCT
      34     is and will stay 0).  The instruction pattern is
      35         b2 ff 0f ff        trap4   4095(%r0)  */
      36  
      37  #define RSEQ_SIG        0xB2FF0FFF