sysdeps/unix/sysv/linux/mips/unwind-arch.h

   1 /* Return backtrace of current program state.  Arch-specific bits.
   2    Copyright (C) 2020-2021 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 _UNWIND_ARCH_H
  20 #define _UNWIND_ARCH_H
  21
  22 #include <stdint.h>
  23
  24 /* MIPS fallback code handle a frame where its FDE can not be obtained
  25    (for instance a signal frame) by reading the kernel allocated signal frame
  26    and adding '2' to the value of 'sc_pc' [1].  The added value is used to
  27    recognize an end of an EH region on mips16 [2].
  28
  29    The idea here is to adjust the obtained signal frame ADDR value and remove
  30    the libgcc added value by checking if the previous frame is a signal frame
  31    one.
  32
  33    [1] libgcc/config/mips/linux-unwind.h from gcc code.
  34    [2] gcc/config/mips/mips.h from gcc code.  */
  35
  36 static inline void *
  37 unwind_arch_adjustment (void *prev, void *addr)
  38 {
  39   uint32_t *pc = (uint32_t *) prev;
  40
  41   if (pc == NULL)
  42     return addr;
  43
  44   /* For MIPS16 or microMIPS frame libgcc makes no adjustment.  */
  45   if ((uintptr_t) pc & 0x3)
  46     return addr;
  47
  48   /* The vDSO containes either
  49
  50      24021061 li v0, 0x1061 (rt_sigreturn)
  51      0000000c syscall
  52         or
  53      24021017 li v0, 0x1017 (sigreturn)
  54      0000000c syscall  */
  55   if (pc[1] != 0x0000000c)
  56     return addr;
  57 #if _MIPS_SIM == _ABIO32
  58   if (pc[0] == (0x24020000 | __NR_sigreturn))
  59     return (void *) ((uintptr_t) addr - 2);
  60 #endif
  61   if (pc[0] == (0x24020000 | __NR_rt_sigreturn))
  62     return (void *) ((uintptr_t) addr - 2);
  63
  64   return addr;
  65 }
  66
  67 #endif