gdb/alpha-linux-tdep.c

   1 /* Target-dependent code for GNU/Linux on Alpha.
   2    Copyright 2002 Free Software Foundation, Inc.
   3
   4    This file is part of GDB.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program; if not, write to the Free Software
  18    Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include "defs.h"
  22 #include "gdbcore.h"
  23 #include "value.h"
  24
  25 #include "alpha-tdep.h"
  26
  27 /* Under GNU/Linux, signal handler invocations can be identified by the
  28    designated code sequence that is used to return from a signal
  29    handler.  In particular, the return address of a signal handler
  30    points to the following sequence (the first instruction is quadword
  31    aligned):
  32
  33    bis $30,$30,$16
  34    addq $31,0x67,$0
  35    call_pal callsys
  36
  37    Each instruction has a unique encoding, so we simply attempt to
  38    match the instruction the pc is pointing to with any of the above
  39    instructions.  If there is a hit, we know the offset to the start
  40    of the designated sequence and can then check whether we really are
  41    executing in a designated sequence.  If not, -1 is returned,
  42    otherwise the offset from the start of the desingated sequence is
  43    returned.
  44
  45    There is a slight chance of false hits: code could jump into the
  46    middle of the designated sequence, in which case there is no
  47    guarantee that we are in the middle of a sigreturn syscall.  Don't
  48    think this will be a problem in praxis, though.  */
  49 LONGEST
  50 alpha_linux_sigtramp_offset (CORE_ADDR pc)
  51 {
  52   unsigned int i[3], w;
  53   long off;
  54
  55   if (read_memory_nobpt (pc, (char *) &w, 4) != 0)
  56     return -1;
  57
  58   off = -1;
  59   switch (w)
  60     {
  61     case 0x47de0410:
  62       off = 0;
  63       break;                    /* bis $30,$30,$16 */
  64     case 0x43ecf400:
  65       off = 4;
  66       break;                    /* addq $31,0x67,$0 */
  67     case 0x00000083:
  68       off = 8;
  69       break;                    /* call_pal callsys */
  70     default:
  71       return -1;
  72     }
  73   pc -= off;
  74   if (pc & 0x7)
  75     {
  76       /* designated sequence is not quadword aligned */
  77       return -1;
  78     }
  79   if (read_memory_nobpt (pc, (char *) i, sizeof (i)) != 0)
  80     return -1;
  81
  82   if (i[0] == 0x47de0410 && i[1] == 0x43ecf400 && i[2] == 0x00000083)
  83     return off;
  84
  85   return -1;
  86 }
  87
  88 static int
  89 alpha_linux_pc_in_sigtramp (CORE_ADDR pc, char *func_name)
  90 {
  91   return (alpha_linux_sigtramp_offset (pc) >= 0);
  92 }
  93
  94 static void
  95 alpha_linux_init_abi (struct gdbarch_info info,
  96                       struct gdbarch *gdbarch)
  97 {
  98   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
  99
 100   set_gdbarch_pc_in_sigtramp (gdbarch, alpha_linux_pc_in_sigtramp);
 101
 102   tdep->dynamic_sigtramp_offset = alpha_linux_sigtramp_offset;
 103
 104   tdep->jb_pc = 2;
 105   tdep->jb_elt_size = 8;
 106 }
 107
 108 void
 109 _initialize_alpha_linux_tdep (void)
 110 {
 111   alpha_gdbarch_register_os_abi (ALPHA_ABI_LINUX, alpha_linux_init_abi);
 112 }