1  /* Dynamic loading of the libgcc unwinder.  MIPS customization.
       2     Copyright (C) 2020-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #ifndef _ARCH_UNWIND_LINK_H
      20  #define _ARCH_UNWIND_LINK_H
      21  
      22  #include <stdint.h>
      23  #include <sys/syscall.h>
      24  
      25  #define UNWIND_LINK_GETIP 1
      26  #define UNWIND_LINK_FRAME_STATE_FOR 1
      27  #define UNWIND_LINK_FRAME_ADJUSTMENT 1
      28  #define UNWIND_LINK_EXTRA_FIELDS
      29  #define UNWIND_LINK_EXTRA_INIT
      30  
      31  /* MIPS fallback code handle a frame where its FDE can not be obtained
      32     (for instance a signal frame) by reading the kernel allocated signal frame
      33     and adding '2' to the value of 'sc_pc' [1].  The added value is used to
      34     recognize an end of an EH region on mips16 [2].
      35  
      36     The idea here is to adjust the obtained signal frame ADDR value and remove
      37     the libgcc added value by checking if the previous frame is a signal frame
      38     one.
      39  
      40     [1] libgcc/config/mips/linux-unwind.h from gcc code.
      41     [2] gcc/config/mips/mips.h from gcc code.  */
      42  
      43  static inline void *
      44  unwind_arch_adjustment (void *prev, void *addr)
      45  {
      46    uint32_t *pc = (uint32_t *) prev;
      47  
      48    if (pc == NULL)
      49      return addr;
      50  
      51    /* For MIPS16 or microMIPS frame libgcc makes no adjustment.  */
      52    if ((uintptr_t) pc & 0x3)
      53      return addr;
      54  
      55    /* The vDSO contains either
      56  
      57       24021061 li v0, 0x1061 (rt_sigreturn)
      58       0000000c syscall
      59          or
      60       24021017 li v0, 0x1017 (sigreturn)
      61       0000000c syscall  */
      62    if (pc[1] != 0x0000000c)
      63      return addr;
      64  #if _MIPS_SIM == _ABIO32
      65    if (pc[0] == (0x24020000 | __NR_sigreturn))
      66      return (void *) ((uintptr_t) addr - 2);
      67  #endif
      68    if (pc[0] == (0x24020000 | __NR_rt_sigreturn))
      69      return (void *) ((uintptr_t) addr - 2);
      70  
      71    return addr;
      72  }
      73  
      74  #endif /* _ARCH_UNWIND_LINK_H */