1/* Native-dependent code for OpenBSD/i386.
2
3   Copyright (C) 2002-2023 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
34static int
35i386obsd_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
91static i386_bsd_nat_target<obsd_nat_target> the_i386_obsd_nat_target;
92
93void _initialize_i386obsd_nat ();
94void
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}
128