gdb/i386-obsd-nat.c

   1 /* Native-dependent code for OpenBSD/i386.
   2
   3    Copyright (C) 2002-2021 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "defs.h"
  21 #include "gdbcore.h"
  22 #include "regcache.h"
  23 #include "target.h"
  24
  25 #include <sys/sysctl.h>
  26 #include <machine/frame.h>
  27 #include <machine/pcb.h>
  28
  29 #include "i386-tdep.h"
  30 #include "i386-bsd-nat.h"
  31 #include "obsd-nat.h"
  32 #include "bsd-kvm.h"
  33
  34 static int
  35 i386obsd_supply_pcb (struct regcache *regcache, struct pcb *pcb)
  36 {
  37   struct gdbarch *gdbarch = regcache->arch ();
  38   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
  39   struct switchframe sf;
  40
  41   /* The following is true for OpenBSD 3.6:
  42
  43      The pcb contains %esp and %ebp at the point of the context switch
  44      in cpu_switch().  At that point we have a stack frame as
  45      described by `struct switchframe', which for OpenBSD 3.6 has the
  46      following layout:
  47
  48      interrupt level
  49      %edi
  50      %esi
  51      %ebx
  52      %eip
  53
  54      we reconstruct the register state as it would look when we just
  55      returned from cpu_switch().  */
  56
  57   /* The stack pointer shouldn't be zero.  */
  58   if (pcb->pcb_esp == 0)
  59     return 0;
  60
  61   /* Read the stack frame, and check its validity.  We do this by
  62      checking if the saved interrupt priority level in the stack frame
  63      looks reasonable..  */
  64 #ifdef PCB_SAVECTX
  65   if ((pcb->pcb_flags & PCB_SAVECTX) == 0)
  66     {
  67       /* Yes, we have a frame that matches cpu_switch().  */
  68       read_memory (pcb->pcb_esp, (gdb_byte *) &sf, sizeof sf);
  69       pcb->pcb_esp += sizeof (struct switchframe);
  70       regcache->raw_supply (I386_EDI_REGNUM, &sf.sf_edi);
  71       regcache->raw_supply (I386_ESI_REGNUM, &sf.sf_esi);
  72       regcache->raw_supply (I386_EBX_REGNUM, &sf.sf_ebx);
  73       regcache->raw_supply (I386_EIP_REGNUM, &sf.sf_eip);
  74     }
  75   else
  76 #endif
  77     {
  78       /* No, the pcb must have been last updated by savectx().  */
  79       pcb->pcb_esp = pcb->pcb_ebp;
  80       pcb->pcb_ebp = read_memory_integer(pcb->pcb_esp, 4, byte_order);
  81       sf.sf_eip = read_memory_integer(pcb->pcb_esp + 4, 4, byte_order);
  82       regcache->raw_supply (I386_EIP_REGNUM, &sf.sf_eip);
  83     }
  84
  85   regcache->raw_supply (I386_EBP_REGNUM, &pcb->pcb_ebp);
  86   regcache->raw_supply (I386_ESP_REGNUM, &pcb->pcb_esp);
  87
  88   return 1;
  89 }
  90
  91 static i386_bsd_nat_target<obsd_nat_target> the_i386_obsd_nat_target;
  92
  93 void _initialize_i386obsd_nat ();
  94 void
  95 _initialize_i386obsd_nat ()
  96 {
  97   add_inf_child_target (&i386_obsd_nat_target);
  98
  99   /* Support debugging kernel virtual memory images.  */
 100   bsd_kvm_add_target (i386obsd_supply_pcb);
 101
 102   /* OpenBSD provides a vm.psstrings sysctl that we can use to locate
 103      the sigtramp.  That way we can still recognize a sigtramp if its
 104      location is changed in a new kernel.  This is especially
 105      important for OpenBSD, since it uses a different memory layout
 106      than NetBSD, yet we cannot distinguish between the two.
 107
 108      Of course this is still based on the assumption that the sigtramp
 109      is placed directly under the location where the program arguments
 110      and environment can be found.  */
 111 #ifdef VM_PSSTRINGS
 112   {
 113     struct _ps_strings _ps;
 114     int mib[2];
 115     size_t len;
 116
 117     mib[0] = CTL_VM;
 118     mib[1] = VM_PSSTRINGS;
 119     len = sizeof (_ps);
 120     if (sysctl (mib, 2, &_ps, &len, NULL, 0) == 0)
 121       {
 122         i386obsd_sigtramp_start_addr = (u_long) _ps.val - 128;
 123         i386obsd_sigtramp_end_addr = (u_long) _ps.val;
 124       }
 125   }
 126 #endif
 127 }