gdb/i386-obsd-nat.c

   1 /* Native-dependent code for OpenBSD/i386.
   2
   3    Copyright (C) 2002-2024 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 "gdbcore.h"
  21 #include "regcache.h"
  22 #include "target.h"
  23
  24 #include <sys/sysctl.h>
  25 #include <machine/frame.h>
  26 #include <machine/pcb.h>
  27
  28 #include "i386-tdep.h"
  29 #include "i386-bsd-nat.h"
  30 #include "obsd-nat.h"
  31 #include "bsd-kvm.h"
  32
  33 static int
  34 i386obsd_supply_pcb (struct regcache *regcache, struct pcb *pcb)
  35 {
  36   struct gdbarch *gdbarch = regcache->arch ();
  37   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
  38   struct switchframe sf;
  39
  40   /* The following is true for OpenBSD 3.6:
  41
  42      The pcb contains %esp and %ebp at the point of the context switch
  43      in cpu_switch().  At that point we have a stack frame as
  44      described by `struct switchframe', which for OpenBSD 3.6 has the
  45      following layout:
  46
  47      interrupt level
  48      %edi
  49      %esi
  50      %ebx
  51      %eip
  52
  53      we reconstruct the register state as it would look when we just
  54      returned from cpu_switch().  */
  55
  56   /* The stack pointer shouldn't be zero.  */
  57   if (pcb->pcb_esp == 0)
  58     return 0;
  59
  60   /* Read the stack frame, and check its validity.  We do this by
  61      checking if the saved interrupt priority level in the stack frame
  62      looks reasonable..  */
  63 #ifdef PCB_SAVECTX
  64   if ((pcb->pcb_flags & PCB_SAVECTX) == 0)
  65     {
  66       /* Yes, we have a frame that matches cpu_switch().  */
  67       read_memory (pcb->pcb_esp, (gdb_byte *) &sf, sizeof sf);
  68       pcb->pcb_esp += sizeof (struct switchframe);
  69       regcache->raw_supply (I386_EDI_REGNUM, &sf.sf_edi);
  70       regcache->raw_supply (I386_ESI_REGNUM, &sf.sf_esi);
  71       regcache->raw_supply (I386_EBX_REGNUM, &sf.sf_ebx);
  72       regcache->raw_supply (I386_EIP_REGNUM, &sf.sf_eip);
  73     }
  74   else
  75 #endif
  76     {
  77       /* No, the pcb must have been last updated by savectx().  */
  78       pcb->pcb_esp = pcb->pcb_ebp;
  79       pcb->pcb_ebp = read_memory_integer(pcb->pcb_esp, 4, byte_order);
  80       sf.sf_eip = read_memory_integer(pcb->pcb_esp + 4, 4, byte_order);
  81       regcache->raw_supply (I386_EIP_REGNUM, &sf.sf_eip);
  82     }
  83
  84   regcache->raw_supply (I386_EBP_REGNUM, &pcb->pcb_ebp);
  85   regcache->raw_supply (I386_ESP_REGNUM, &pcb->pcb_esp);
  86
  87   return 1;
  88 }
  89
  90 static i386_bsd_nat_target<obsd_nat_target> the_i386_obsd_nat_target;
  91
  92 void _initialize_i386obsd_nat ();
  93 void
  94 _initialize_i386obsd_nat ()
  95 {
  96   add_inf_child_target (&i386_obsd_nat_target);
  97
  98   /* Support debugging kernel virtual memory images.  */
  99   bsd_kvm_add_target (i386obsd_supply_pcb);
 100
 101   /* OpenBSD provides a vm.psstrings sysctl that we can use to locate
 102      the sigtramp.  That way we can still recognize a sigtramp if its
 103      location is changed in a new kernel.  This is especially
 104      important for OpenBSD, since it uses a different memory layout
 105      than NetBSD, yet we cannot distinguish between the two.
 106
 107      Of course this is still based on the assumption that the sigtramp
 108      is placed directly under the location where the program arguments
 109      and environment can be found.  */
 110 #ifdef VM_PSSTRINGS
 111   {
 112     struct _ps_strings _ps;
 113     int mib[2];
 114     size_t len;
 115
 116     mib[0] = CTL_VM;
 117     mib[1] = VM_PSSTRINGS;
 118     len = sizeof (_ps);
 119     if (sysctl (mib, 2, &_ps, &len, NULL, 0) == 0)
 120       {
 121         i386obsd_sigtramp_start_addr = (u_long) _ps.val - 128;
 122         i386obsd_sigtramp_end_addr = (u_long) _ps.val;
 123       }
 124   }
 125 #endif
 126 }