Add minimal and functional NetBSD/amd64 gdbserver

Implement the following functionality: create_inferior,
post_create_inferior, attach, kill, detach, mourn, join, thread_alive,
resume, wait, fetch_registers, store_registers, read_memory, write_memory,
request_interrupt, supports_read_auxv, read_auxv,
supports_hardware_single_step, sw_breakpoint_from_kind,
supports_z_point_type, insert_point, remove_point,
stopped_by_sw_breakpoint, supports_qxfer_siginfo, qxfer_siginfo,
supports_stopped_by_sw_breakpoint, supports_non_stop,
supports_multi_process, supports_fork_events, supports_vfork_events,
supports_exec_events, supports_disable_randomization,
supports_qxfer_libraries_svr4, qxfer_libraries_svr4,
supports_pid_to_exec_file, pid_to_exec_file, thread_name,
supports_catch_syscall.

The only CPU architecture supported: x86_64.

Implement only support for hardware assisted single step and
software breakpoint.

Implement support only for regular X86 registers, thus no FPU.

gdbserver/ChangeLog:

       * netbsd-low.cc: Add.
       * netbsd-low.h: Likewise.
       * netbsd-amd64-low.cc: Likewise.
       * Makefile.in (SFILES): Register "netbsd-low.cc", "netbsd-low.h",
       "netbsd-amd64-low.cc".
       * configure.srv: Add x86_64-*-netbsd*.

6 files changed, 1686 insertions, 0 deletions

diff --git a/gdbserver/ChangeLog b/gdbserver/ChangeLog
index e437493..0c8af7c 100644
--- a/gdbserver/ChangeLog
+++ b/gdbserver/ChangeLog
@@ -1,3 +1,12 @@
+2020-09-10  Kamil Rytarowski  <n54@gmx.com>
+
+	* netbsd-low.cc: Add.
+	* netbsd-low.h: Likewise.
+	* netbsd-amd64-low.cc: Likewise.
+	* Makefile.in (SFILES): Register "netbsd-low.cc", "netbsd-low.h",
+	"netbsd-amd64-low.cc".
+	* configure.srv: Add x86_64-*-netbsd*.
+
 2020-08-13  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* server.cc (captured_main): Accept multiple `--selftest=`
diff --git a/gdbserver/Makefile.in b/gdbserver/Makefile.in
index 9d7687b..b0bad0c 100644
--- a/gdbserver/Makefile.in
+++ b/gdbserver/Makefile.in
@@ -193,6 +193,9 @@ SFILES = \
 	$(srcdir)/linux-x86-low.cc \
 	$(srcdir)/linux-xtensa-low.cc \
 	$(srcdir)/mem-break.cc \
+	$(srcdir)/netbsd-amd64-low.cc \
+	$(srcdir)/netbsd-low.cc \
+	$(srcdir)/netbsd-low.h \
 	$(srcdir)/proc-service.cc \
 	$(srcdir)/proc-service.list \
 	$(srcdir)/regcache.cc \
diff --git a/gdbserver/configure.srv b/gdbserver/configure.srv
index 5e33bd9..b9a3703 100644
--- a/gdbserver/configure.srv
+++ b/gdbserver/configure.srv
@@ -349,6 +349,12 @@ case "${gdbserver_host}" in
 			srv_tgtobj="${srv_tgtobj} nat/windows-nat.o"
 			srv_tgtobj="${srv_tgtobj} arch/amd64.o arch/i386.o"
 			;;
+  x86_64-*-netbsd*)	srv_regobj=""
+			srv_tgtobj="netbsd-low.o netbsd-amd64-low.o fork-child.o"
+			srv_tgtobj="${srv_tgtobj} nat/fork-inferior.o"
+			srv_tgtobj="${srv_tgtobj} nat/netbsd-nat.o"
+			srv_tgtobj="${srv_tgtobj} arch/amd64.o"
+			;;
 
   xtensa*-*-linux*)	srv_regobj=reg-xtensa.o
 			srv_tgtobj="$srv_linux_obj linux-xtensa-low.o"
diff --git a/gdbserver/netbsd-amd64-low.cc b/gdbserver/netbsd-amd64-low.cc
new file mode 100644
index 0000000..9b8ea9b
--- /dev/null
+++ b/gdbserver/netbsd-amd64-low.cc
@@ -0,0 +1,187 @@
+/* Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <sys/types.h>
+#include <sys/ptrace.h>
+#include <limits.h>
+
+#include "server.h"
+#include "netbsd-low.h"
+#include "gdbsupport/x86-xstate.h"
+#include "arch/amd64.h"
+#include "x86-tdesc.h"
+#include "tdesc.h"
+
+/* The index of various registers inside the regcache.  */
+
+enum netbsd_x86_64_gdb_regnum
+{
+  AMD64_RAX_REGNUM,	     /* %rax */
+  AMD64_RBX_REGNUM,	     /* %rbx */
+  AMD64_RCX_REGNUM,	     /* %rcx */
+  AMD64_RDX_REGNUM,	     /* %rdx */
+  AMD64_RSI_REGNUM,	     /* %rsi */
+  AMD64_RDI_REGNUM,	     /* %rdi */
+  AMD64_RBP_REGNUM,	     /* %rbp */
+  AMD64_RSP_REGNUM,	     /* %rsp */
+  AMD64_R8_REGNUM,	      /* %r8 */
+  AMD64_R9_REGNUM,	      /* %r9 */
+  AMD64_R10_REGNUM,	     /* %r10 */
+  AMD64_R11_REGNUM,	     /* %r11 */
+  AMD64_R12_REGNUM,	     /* %r12 */
+  AMD64_R13_REGNUM,	     /* %r13 */
+  AMD64_R14_REGNUM,	     /* %r14 */
+  AMD64_R15_REGNUM,	     /* %r15 */
+  AMD64_RIP_REGNUM,	     /* %rip */
+  AMD64_EFLAGS_REGNUM,	  /* %eflags */
+  AMD64_CS_REGNUM,	      /* %cs */
+  AMD64_SS_REGNUM,	      /* %ss */
+  AMD64_DS_REGNUM,	      /* %ds */
+  AMD64_ES_REGNUM,	      /* %es */
+  AMD64_FS_REGNUM,	      /* %fs */
+  AMD64_GS_REGNUM,	      /* %gs */
+  AMD64_ST0_REGNUM = 24,     /* %st0 */
+  AMD64_ST1_REGNUM,	     /* %st1 */
+  AMD64_FCTRL_REGNUM = AMD64_ST0_REGNUM + 8,
+  AMD64_FSTAT_REGNUM = AMD64_ST0_REGNUM + 9,
+  AMD64_FTAG_REGNUM = AMD64_ST0_REGNUM + 10,
+  AMD64_XMM0_REGNUM = 40,   /* %xmm0 */
+  AMD64_XMM1_REGNUM,	    /* %xmm1 */
+  AMD64_MXCSR_REGNUM = AMD64_XMM0_REGNUM + 16,
+  AMD64_YMM0H_REGNUM,	   /* %ymm0h */
+  AMD64_YMM15H_REGNUM = AMD64_YMM0H_REGNUM + 15,
+  AMD64_BND0R_REGNUM = AMD64_YMM15H_REGNUM + 1,
+  AMD64_BND3R_REGNUM = AMD64_BND0R_REGNUM + 3,
+  AMD64_BNDCFGU_REGNUM,
+  AMD64_BNDSTATUS_REGNUM,
+  AMD64_XMM16_REGNUM,
+  AMD64_XMM31_REGNUM = AMD64_XMM16_REGNUM + 15,
+  AMD64_YMM16H_REGNUM,
+  AMD64_YMM31H_REGNUM = AMD64_YMM16H_REGNUM + 15,
+  AMD64_K0_REGNUM,
+  AMD64_K7_REGNUM = AMD64_K0_REGNUM + 7,
+  AMD64_ZMM0H_REGNUM,
+  AMD64_ZMM31H_REGNUM = AMD64_ZMM0H_REGNUM + 31,
+  AMD64_PKRU_REGNUM,
+  AMD64_FSBASE_REGNUM,
+  AMD64_GSBASE_REGNUM
+};
+
+/* The fill_function for the general-purpose register set.  */
+
+static void
+netbsd_x86_64_fill_gregset (struct regcache *regcache, char *buf)
+{
+  struct reg *r = (struct reg *) buf;
+
+#define netbsd_x86_64_collect_gp(regnum, fld) do {		\
+    collect_register (regcache, regnum, &r->regs[_REG_##fld]);	\
+  } while (0)
+
+  netbsd_x86_64_collect_gp (AMD64_RAX_REGNUM, RAX);
+  netbsd_x86_64_collect_gp (AMD64_RBX_REGNUM, RBX);
+  netbsd_x86_64_collect_gp (AMD64_RCX_REGNUM, RCX);
+  netbsd_x86_64_collect_gp (AMD64_RDX_REGNUM, RDX);
+  netbsd_x86_64_collect_gp (AMD64_RSI_REGNUM, RSI);
+  netbsd_x86_64_collect_gp (AMD64_RDI_REGNUM, RDI);
+  netbsd_x86_64_collect_gp (AMD64_RBP_REGNUM, RBP);
+  netbsd_x86_64_collect_gp (AMD64_RSP_REGNUM, RSP);
+  netbsd_x86_64_collect_gp (AMD64_R8_REGNUM, R8);
+  netbsd_x86_64_collect_gp (AMD64_R9_REGNUM, R9);
+  netbsd_x86_64_collect_gp (AMD64_R10_REGNUM, R10);
+  netbsd_x86_64_collect_gp (AMD64_R11_REGNUM, R11);
+  netbsd_x86_64_collect_gp (AMD64_R12_REGNUM, R12);
+  netbsd_x86_64_collect_gp (AMD64_R13_REGNUM, R13);
+  netbsd_x86_64_collect_gp (AMD64_R14_REGNUM, R14);
+  netbsd_x86_64_collect_gp (AMD64_R15_REGNUM, R15);
+  netbsd_x86_64_collect_gp (AMD64_RIP_REGNUM, RIP);
+  netbsd_x86_64_collect_gp (AMD64_EFLAGS_REGNUM, RFLAGS);
+  netbsd_x86_64_collect_gp (AMD64_CS_REGNUM, CS);
+  netbsd_x86_64_collect_gp (AMD64_SS_REGNUM, SS);
+  netbsd_x86_64_collect_gp (AMD64_DS_REGNUM, DS);
+  netbsd_x86_64_collect_gp (AMD64_ES_REGNUM, ES);
+  netbsd_x86_64_collect_gp (AMD64_FS_REGNUM, FS);
+  netbsd_x86_64_collect_gp (AMD64_GS_REGNUM, GS);
+}
+
+/* The store_function for the general-purpose register set.  */
+
+static void
+netbsd_x86_64_store_gregset (struct regcache *regcache, const char *buf)
+{
+  struct reg *r = (struct reg *) buf;
+
+#define netbsd_x86_64_supply_gp(regnum, fld) do {		\
+    supply_register (regcache, regnum, &r->regs[_REG_##fld]);	\
+  } while(0)
+
+  netbsd_x86_64_supply_gp (AMD64_RAX_REGNUM, RAX);
+  netbsd_x86_64_supply_gp (AMD64_RBX_REGNUM, RBX);
+  netbsd_x86_64_supply_gp (AMD64_RCX_REGNUM, RCX);
+  netbsd_x86_64_supply_gp (AMD64_RDX_REGNUM, RDX);
+  netbsd_x86_64_supply_gp (AMD64_RSI_REGNUM, RSI);
+  netbsd_x86_64_supply_gp (AMD64_RDI_REGNUM, RDI);
+  netbsd_x86_64_supply_gp (AMD64_RBP_REGNUM, RBP);
+  netbsd_x86_64_supply_gp (AMD64_RSP_REGNUM, RSP);
+  netbsd_x86_64_supply_gp (AMD64_R8_REGNUM, R8);
+  netbsd_x86_64_supply_gp (AMD64_R9_REGNUM, R9);
+  netbsd_x86_64_supply_gp (AMD64_R10_REGNUM, R10);
+  netbsd_x86_64_supply_gp (AMD64_R11_REGNUM, R11);
+  netbsd_x86_64_supply_gp (AMD64_R12_REGNUM, R12);
+  netbsd_x86_64_supply_gp (AMD64_R13_REGNUM, R13);
+  netbsd_x86_64_supply_gp (AMD64_R14_REGNUM, R14);
+  netbsd_x86_64_supply_gp (AMD64_R15_REGNUM, R15);
+  netbsd_x86_64_supply_gp (AMD64_RIP_REGNUM, RIP);
+  netbsd_x86_64_supply_gp (AMD64_EFLAGS_REGNUM, RFLAGS);
+  netbsd_x86_64_supply_gp (AMD64_CS_REGNUM, CS);
+  netbsd_x86_64_supply_gp (AMD64_SS_REGNUM, SS);
+  netbsd_x86_64_supply_gp (AMD64_DS_REGNUM, DS);
+  netbsd_x86_64_supply_gp (AMD64_ES_REGNUM, ES);
+  netbsd_x86_64_supply_gp (AMD64_FS_REGNUM, FS);
+  netbsd_x86_64_supply_gp (AMD64_GS_REGNUM, GS);
+}
+
+/* Implements the netbsd_target_ops.arch_setup routine.  */
+
+static void
+netbsd_x86_64_arch_setup (void)
+{
+  struct target_desc *tdesc
+    = amd64_create_target_description (X86_XSTATE_SSE_MASK, false, false, false);
+
+  init_target_desc (tdesc, amd64_expedite_regs);
+
+  netbsd_tdesc = tdesc;
+}
+
+/* Description of all the x86-netbsd register sets.  */
+
+struct netbsd_regset_info netbsd_target_regsets[] =
+{
+ /* General Purpose Registers.  */
+ {PT_GETREGS, PT_SETREGS, sizeof (struct reg),
+  netbsd_x86_64_fill_gregset, netbsd_x86_64_store_gregset},
+ /* End of list marker.  */
+ {0, 0, -1, NULL, NULL }
+};
+
+/* The netbsd_target_ops vector for x86-netbsd.  */
+
+struct netbsd_target_ops the_low_target =
+{
+ netbsd_x86_64_arch_setup,
+};
diff --git a/gdbserver/netbsd-low.cc b/gdbserver/netbsd-low.cc
new file mode 100644
index 0000000..8b13b67
--- /dev/null
+++ b/gdbserver/netbsd-low.cc
@@ -0,0 +1,1327 @@
+/* Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "server.h"
+#include "target.h"
+#include "netbsd-low.h"
+#include "nat/netbsd-nat.h"
+
+#include <sys/param.h>
+#include <sys/types.h>
+
+#include <sys/ptrace.h>
+#include <sys/sysctl.h>
+
+#include <limits.h>
+#include <unistd.h>
+#include <signal.h>
+
+#include <elf.h>
+
+#include <type_traits>
+
+#include "gdbsupport/eintr.h"
+#include "gdbsupport/gdb_wait.h"
+#include "gdbsupport/filestuff.h"
+#include "gdbsupport/common-inferior.h"
+#include "nat/fork-inferior.h"
+#include "hostio.h"
+
+int using_threads = 1;
+
+const struct target_desc *netbsd_tdesc;
+
+/* Call add_process with the given parameters, and initialize
+   the process' private data.  */
+
+static void
+netbsd_add_process (int pid, int attached)
+{
+  struct process_info *proc = add_process (pid, attached);
+  proc->tdesc = netbsd_tdesc;
+  proc->priv = nullptr;
+}
+
+/* Callback used by fork_inferior to start tracing the inferior.  */
+
+static void
+netbsd_ptrace_fun ()
+{
+  /* Switch child to its own process group so that signals won't
+     directly affect GDBserver. */
+  if (setpgid (0, 0) < 0)
+    trace_start_error_with_name (("setpgid"));
+
+  if (ptrace (PT_TRACE_ME, 0, nullptr, 0) < 0)
+    trace_start_error_with_name (("ptrace"));
+
+  /* If GDBserver is connected to gdb via stdio, redirect the inferior's
+     stdout to stderr so that inferior i/o doesn't corrupt the connection.
+     Also, redirect stdin to /dev/null.  */
+  if (remote_connection_is_stdio ())
+    {
+      if (close (0) < 0)
+	trace_start_error_with_name (("close"));
+      if (open ("/dev/null", O_RDONLY) < 0)
+	trace_start_error_with_name (("open"));
+      if (dup2 (2, 1) < 0)
+	trace_start_error_with_name (("dup2"));
+      if (write (2, "stdin/stdout redirected\n",
+		 sizeof ("stdin/stdout redirected\n") - 1) < 0)
+	{
+	  /* Errors ignored.  */
+	}
+    }
+}
+
+/* Implement the create_inferior method of the target_ops vector.  */
+
+int
+netbsd_process_target::create_inferior (const char *program,
+					const std::vector<char *> &program_args)
+{
+  std::string str_program_args = construct_inferior_arguments (program_args);
+
+  pid_t pid = fork_inferior (program, str_program_args.c_str (),
+			     get_environ ()->envp (), netbsd_ptrace_fun,
+			     nullptr, nullptr, nullptr, nullptr);
+
+  netbsd_add_process (pid, 0);
+
+  post_fork_inferior (pid, program);
+
+  return pid;
+}
+
+/* Implement the post_create_inferior target_ops method.  */
+
+void
+netbsd_process_target::post_create_inferior ()
+{
+  pid_t pid = current_process ()->pid;
+  netbsd_nat::enable_proc_events (pid);
+}
+
+/* Implement the attach target_ops method.  */
+
+int
+netbsd_process_target::attach (unsigned long pid)
+{
+  /* Unimplemented.  */
+  return -1;
+}
+
+/* Returns true if GDB is interested in any child syscalls.  */
+
+static bool
+gdb_catching_syscalls_p (pid_t pid)
+{
+  struct process_info *proc = find_process_pid (pid);
+  return !proc->syscalls_to_catch.empty ();
+}
+
+/* Implement the resume target_ops method.  */
+
+void
+netbsd_process_target::resume (struct thread_resume *resume_info, size_t n)
+{
+  ptid_t resume_ptid = resume_info[0].thread;
+  const int signal = resume_info[0].sig;
+  const bool step = resume_info[0].kind == resume_step;
+
+  if (resume_ptid == minus_one_ptid)
+    resume_ptid = ptid_of (current_thread);
+
+  const pid_t pid = resume_ptid.pid ();
+  const lwpid_t lwp = resume_ptid.lwp ();
+  regcache_invalidate_pid (pid);
+
+  auto fn
+    = [&] (ptid_t ptid)
+      {
+	if (step)
+	  {
+	    if (ptid.lwp () == lwp || n != 1)
+	      {
+		if (ptrace (PT_SETSTEP, pid, NULL, ptid.lwp ()) == -1)
+		  perror_with_name (("ptrace"));
+		if (ptrace (PT_RESUME, pid, NULL, ptid.lwp ()) == -1)
+		  perror_with_name (("ptrace"));
+	      }
+	    else
+	      {
+		if (ptrace (PT_CLEARSTEP, pid, NULL, ptid.lwp ()) == -1)
+		  perror_with_name (("ptrace"));
+		if (ptrace (PT_SUSPEND, pid, NULL, ptid.lwp ()) == -1)
+		  perror_with_name (("ptrace"));
+	      }
+	  }
+	else
+	  {
+	    if (ptrace (PT_CLEARSTEP, pid, NULL, ptid.lwp ()) == -1)
+	      perror_with_name (("ptrace"));
+	    if (ptrace (PT_RESUME, pid, NULL, ptid.lwp ()) == -1)
+	      perror_with_name (("ptrace"));
+	  }
+      };
+
+  netbsd_nat::for_each_thread (pid, fn);
+
+  int request = gdb_catching_syscalls_p (pid) ? PT_CONTINUE : PT_SYSCALL;
+
+  errno = 0;
+  ptrace (request, pid, (void *)1, signal);
+  if (errno)
+    perror_with_name (("ptrace"));
+}
+
+/* Returns true if GDB is interested in the reported SYSNO syscall.  */
+
+static bool
+netbsd_catch_this_syscall (int sysno)
+{
+  struct process_info *proc = current_process ();
+
+  if (proc->syscalls_to_catch.empty ())
+    return false;
+
+  if (proc->syscalls_to_catch[0] == ANY_SYSCALL)
+    return true;
+
+  for (int iter : proc->syscalls_to_catch)
+    if (iter == sysno)
+      return true;
+
+  return false;
+}
+
+/* Helper function for child_wait and the derivatives of child_wait.
+   HOSTSTATUS is the waitstatus from wait() or the equivalent; store our
+   translation of that in OURSTATUS.  */
+
+static void
+netbsd_store_waitstatus (struct target_waitstatus *ourstatus, int hoststatus)
+{
+  if (WIFEXITED (hoststatus))
+    {
+      ourstatus->kind = TARGET_WAITKIND_EXITED;
+      ourstatus->value.integer = WEXITSTATUS (hoststatus);
+    }
+  else if (!WIFSTOPPED (hoststatus))
+    {
+      ourstatus->kind = TARGET_WAITKIND_SIGNALLED;
+      ourstatus->value.sig = gdb_signal_from_host (WTERMSIG (hoststatus));
+    }
+  else
+    {
+      ourstatus->kind = TARGET_WAITKIND_STOPPED;
+      ourstatus->value.sig = gdb_signal_from_host (WSTOPSIG (hoststatus));
+    }
+}
+
+/* Implement a safe wrapper around waitpid().  */
+
+static pid_t
+netbsd_waitpid (ptid_t ptid, struct target_waitstatus *ourstatus, int options)
+{
+  int status;
+
+  pid_t pid
+    = gdb::handle_eintr<int> (-1, ::waitpid, ptid.pid (), &status, options);
+
+  if (pid == -1)
+    perror_with_name (_("Child process unexpectedly missing"));
+
+  netbsd_store_waitstatus (ourstatus, status);
+  return pid;
+}
+
+
+/* Implement the wait target_ops method.
+
+   Wait for the child specified by PTID to do something.  Return the
+   process ID of the child, or MINUS_ONE_PTID in case of error; store
+   the status in *OURSTATUS.  */
+
+static ptid_t
+netbsd_wait (ptid_t ptid, struct target_waitstatus *ourstatus,
+	     int target_options)
+{
+  pid_t pid = netbsd_waitpid (ptid, ourstatus, target_options);
+  ptid_t wptid = ptid_t (pid);
+
+  if (pid == 0)
+    {
+      gdb_assert (target_options & TARGET_WNOHANG);
+      ourstatus->kind = TARGET_WAITKIND_IGNORE;
+      return null_ptid;
+    }
+
+  gdb_assert (pid != -1);
+
+  /* If the child stopped, keep investigating its status.  */
+  if (ourstatus->kind != TARGET_WAITKIND_STOPPED)
+    return wptid;
+
+  /* Extract the event and thread that received a signal.  */
+  ptrace_siginfo_t psi;
+  if (ptrace (PT_GET_SIGINFO, pid, &psi, sizeof (psi)) == -1)
+    perror_with_name (("ptrace"));
+
+  /* Pick child's siginfo_t.  */
+  siginfo_t *si = &psi.psi_siginfo;
+
+  lwpid_t lwp = psi.psi_lwpid;
+
+  int signo = si->si_signo;
+  const int code = si->si_code;
+
+  /* Construct PTID with a specified thread that received the event.
+     If a signal was targeted to the whole process, lwp is 0.  */
+  wptid = ptid_t (pid, lwp, 0);
+
+  /* Bail out on non-debugger oriented signals.  */
+  if (signo != SIGTRAP)
+    return wptid;
+
+  /* Stop examining non-debugger oriented SIGTRAP codes.  */
+  if (code <= SI_USER || code == SI_NOINFO)
+    return wptid;
+
+  /* Process state for threading events.  */
+  ptrace_state_t pst = {};
+  if (code == TRAP_LWP)
+    if (ptrace (PT_GET_PROCESS_STATE, pid, &pst, sizeof (pst)) == -1)
+      perror_with_name (("ptrace"));
+
+  if (code == TRAP_LWP && pst.pe_report_event == PTRACE_LWP_EXIT)
+    {
+      /* If GDB attaches to a multi-threaded process, exiting
+	 threads might be skipped during post_attach that
+	 have not yet reported their PTRACE_LWP_EXIT event.
+	 Ignore exited events for an unknown LWP.  */
+      thread_info *thr = find_thread_ptid (wptid);
+      if (thr == nullptr)
+	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+      else
+	{
+	  ourstatus->kind = TARGET_WAITKIND_THREAD_EXITED;
+	  /* NetBSD does not store an LWP exit status.  */
+	  ourstatus->value.integer = 0;
+
+	  remove_thread (thr);
+	}
+      return wptid;
+    }
+
+  if (find_thread_ptid (ptid_t (pid)))
+    current_thread = find_thread_ptid (wptid);
+
+  if (code == TRAP_LWP && pst.pe_report_event == PTRACE_LWP_CREATE)
+    {
+      /* If GDB attaches to a multi-threaded process, newborn
+	 threads might be added by nbsd_add_threads that have
+	 not yet reported their PTRACE_LWP_CREATE event.  Ignore
+	 born events for an already-known LWP.  */
+      if (find_thread_ptid (wptid))
+	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+      else
+	{
+	  add_thread (wptid, NULL);
+	  ourstatus->kind = TARGET_WAITKIND_THREAD_CREATED;
+	}
+      return wptid;
+    }
+
+  if (code == TRAP_EXEC)
+    {
+      ourstatus->kind = TARGET_WAITKIND_EXECD;
+      ourstatus->value.execd_pathname
+	= xstrdup (netbsd_nat::pid_to_exec_file (pid));
+      return wptid;
+    }
+
+  if (code == TRAP_TRACE)
+      return wptid;
+
+  if (code == TRAP_SCE || code == TRAP_SCX)
+    {
+      int sysnum = si->si_sysnum;
+
+      if (!netbsd_catch_this_syscall(sysnum))
+	{
+	  /* If the core isn't interested in this event, ignore it.  */
+	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+	  return wptid;
+	}
+
+      ourstatus->kind
+	= ((code == TRAP_SCE) ? TARGET_WAITKIND_SYSCALL_ENTRY :
+	   TARGET_WAITKIND_SYSCALL_RETURN);
+      ourstatus->value.syscall_number = sysnum;
+      return wptid;
+    }
+
+  if (code == TRAP_BRKPT)
+    {
+#ifdef PTRACE_BREAKPOINT_ADJ
+      CORE_ADDR pc;
+      struct reg r;
+      ptrace (PT_GETREGS, pid, &r, psi.psi_lwpid);
+      pc = PTRACE_REG_PC (&r);
+      PTRACE_REG_SET_PC (&r, pc - PTRACE_BREAKPOINT_ADJ);
+      ptrace (PT_SETREGS, pid, &r, psi.psi_lwpid);
+#endif
+      return wptid;
+    }
+
+  /* Unclassified SIGTRAP event.  */
+  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+  return wptid;
+}
+
+/* Implement the wait target_ops method.  */
+
+ptid_t
+netbsd_process_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
+			     int target_options)
+{
+  while (true)
+    {
+      ptid_t wptid = netbsd_wait (ptid, ourstatus, target_options);
+
+      /* Register thread in the gdbcore if a thread was not reported earlier.
+	 This is required after ::create_inferior, when the gdbcore does not
+	 know about the first internal thread.
+	 This may also happen on attach, when an event is registered on a thread
+	 that was not fully initialized during the attach stage.  */
+      if (wptid.lwp () != 0 && !find_thread_ptid (wptid)
+	  && ourstatus->kind != TARGET_WAITKIND_THREAD_EXITED)
+	add_thread (wptid, nullptr);
+
+      switch (ourstatus->kind)
+	{
+	case TARGET_WAITKIND_EXITED:
+	case TARGET_WAITKIND_STOPPED:
+	case TARGET_WAITKIND_SIGNALLED:
+	case TARGET_WAITKIND_FORKED:
+	case TARGET_WAITKIND_VFORKED:
+	case TARGET_WAITKIND_EXECD:
+	case TARGET_WAITKIND_VFORK_DONE:
+	case TARGET_WAITKIND_SYSCALL_ENTRY:
+	case TARGET_WAITKIND_SYSCALL_RETURN:
+	  /* Pass the result to the generic code.  */
+	  return wptid;
+	case TARGET_WAITKIND_THREAD_CREATED:
+	case TARGET_WAITKIND_THREAD_EXITED:
+	  /* The core needlessly stops on these events.  */
+	  /* FALLTHROUGH */
+	case TARGET_WAITKIND_SPURIOUS:
+	  /* Spurious events are unhandled by the gdbserver core.  */
+	  if (ptrace (PT_CONTINUE, current_process ()->pid, (void *) 1, 0)
+	      == -1)
+	    perror_with_name (("ptrace"));
+	  break;
+	default:
+	  error (("Unknown stopped status"));
+	}
+    }
+}
+
+/* Implement the kill target_ops method.  */
+
+int
+netbsd_process_target::kill (process_info *process)
+{
+  pid_t pid = process->pid;
+  if (ptrace (PT_KILL, pid, nullptr, 0) == -1)
+    return -1;
+
+  int status;
+  if (gdb::handle_eintr<int> (-1, ::waitpid, pid, &status, 0) == -1)
+    return -1;
+  mourn (process);
+  return 0;
+}
+
+/* Implement the detach target_ops method.  */
+
+int
+netbsd_process_target::detach (process_info *process)
+{
+  pid_t pid = process->pid;
+
+  ptrace (PT_DETACH, pid, (void *) 1, 0);
+  mourn (process);
+  return 0;
+}
+
+/* Implement the mourn target_ops method.  */
+
+void
+netbsd_process_target::mourn (struct process_info *proc)
+{
+  for_each_thread (proc->pid, remove_thread);
+
+  remove_process (proc);
+}
+
+/* Implement the join target_ops method.  */
+
+void
+netbsd_process_target::join (int pid)
+{
+  /* The PT_DETACH is sufficient to detach from the process.
+     So no need to do anything extra.  */
+}
+
+/* Implement the thread_alive target_ops method.  */
+
+bool
+netbsd_process_target::thread_alive (ptid_t ptid)
+{
+  return netbsd_nat::thread_alive (ptid);
+}
+
+/* Implement the fetch_registers target_ops method.  */
+
+void
+netbsd_process_target::fetch_registers (struct regcache *regcache, int regno)
+{
+  struct netbsd_regset_info *regset = netbsd_target_regsets;
+  ptid_t inferior_ptid = ptid_of (current_thread);
+
+  while (regset->size >= 0)
+    {
+      std::vector<char> buf;
+      buf.resize (regset->size);
+      int res = ptrace (regset->get_request, inferior_ptid.pid (), buf.data (),
+			inferior_ptid.lwp ());
+      if (res == -1)
+	perror_with_name (("ptrace"));
+      regset->store_function (regcache, buf.data ());
+      regset++;
+    }
+}
+
+/* Implement the store_registers target_ops method.  */
+
+void
+netbsd_process_target::store_registers (struct regcache *regcache, int regno)
+{
+  struct netbsd_regset_info *regset = netbsd_target_regsets;
+  ptid_t inferior_ptid = ptid_of (current_thread);
+
+  while (regset->size >= 0)
+    {
+      std::vector<char> buf;
+      buf.resize (regset->size);
+      int res = ptrace (regset->get_request, inferior_ptid.pid (), buf.data (),
+			inferior_ptid.lwp ());
+      if (res == -1)
+	perror_with_name (("ptrace"));
+
+      /* Then overlay our cached registers on that.  */
+      regset->fill_function (regcache, buf.data ());
+      /* Only now do we write the register set.  */
+      res = ptrace (regset->set_request, inferior_ptid.pid (), buf. data (),
+		    inferior_ptid.lwp ());
+      if (res == -1)
+	perror_with_name (("ptrace"));
+      regset++;
+    }
+}
+
+/* Implement the read_memory target_ops method.  */
+
+int
+netbsd_process_target::read_memory (CORE_ADDR memaddr, unsigned char *myaddr,
+				    int size)
+{
+  struct ptrace_io_desc io;
+  io.piod_op = PIOD_READ_D;
+  io.piod_len = size;
+
+  pid_t pid = current_process ()->pid;
+
+  int bytes_read = 0;
+
+  if (size == 0)
+    {
+      /* Zero length write always succeeds.  */
+      return 0;
+    }
+  do
+    {
+      io.piod_offs = (void *)(memaddr + bytes_read);
+      io.piod_addr = myaddr + bytes_read;
+
+      int rv = ptrace (PT_IO, pid, &io, 0);
+      if (rv == -1)
+	return errno;
+      if (io.piod_len == 0)
+	return 0;
+
+      bytes_read += io.piod_len;
+      io.piod_len = size - bytes_read;
+    }
+  while (bytes_read < size);
+
+  return 0;
+}
+
+/* Implement the write_memory target_ops method.  */
+
+int
+netbsd_process_target::write_memory (CORE_ADDR memaddr,
+				     const unsigned char *myaddr, int size)
+{
+  struct ptrace_io_desc io;
+  io.piod_op = PIOD_WRITE_D;
+  io.piod_len = size;
+
+  pid_t pid = current_process ()->pid;
+
+  int bytes_written = 0;
+
+  if (size == 0)
+    {
+      /* Zero length write always succeeds.  */
+      return 0;
+    }
+
+  do
+    {
+      io.piod_addr = (void *)(myaddr + bytes_written);
+      io.piod_offs = (void *)(memaddr + bytes_written);
+
+      int rv = ptrace (PT_IO, pid, &io, 0);
+      if (rv == -1)
+	return errno;
+      if (io.piod_len == 0)
+	return 0;
+
+      bytes_written += io.piod_len;
+      io.piod_len = size - bytes_written;
+    }
+  while (bytes_written < size);
+
+  return 0;
+}
+
+/* Implement the request_interrupt target_ops method.  */
+
+void
+netbsd_process_target::request_interrupt ()
+{
+  ptid_t inferior_ptid = ptid_of (get_first_thread ());
+
+  ::kill (inferior_ptid.pid(), SIGINT);
+}
+
+/* Read the AUX Vector for the specified PID, wrapping the ptrace(2) call
+   with the PIOD_READ_AUXV operation and using the PT_IO standard input
+   and output arguments.  */
+
+static size_t
+netbsd_read_auxv(pid_t pid, void *offs, void *addr, size_t len)
+{
+  struct ptrace_io_desc pio;
+
+  pio.piod_op = PIOD_READ_AUXV;
+  pio.piod_offs = offs;
+  pio.piod_addr = addr;
+  pio.piod_len = len;
+
+  if (ptrace (PT_IO, pid, &pio, 0) == -1)
+    perror_with_name (("ptrace"));
+
+  return pio.piod_len;
+}
+
+/* Copy LEN bytes from inferior's auxiliary vector starting at OFFSET
+   to debugger memory starting at MYADDR.  */
+
+int
+netbsd_process_target::read_auxv (CORE_ADDR offset,
+				  unsigned char *myaddr, unsigned int len)
+{
+  pid_t pid = pid_of (current_thread);
+
+  return netbsd_read_auxv (pid, (void *) (intptr_t) offset, myaddr, len);
+}
+
+bool
+netbsd_process_target::supports_z_point_type (char z_type)
+{
+  switch (z_type)
+    {
+    case Z_PACKET_SW_BP:
+      return true;
+    case Z_PACKET_HW_BP:
+    case Z_PACKET_WRITE_WP:
+    case Z_PACKET_READ_WP:
+    case Z_PACKET_ACCESS_WP:
+    default:
+      return false; /* Not supported.  */
+    }
+}
+
+/* Insert {break/watch}point at address ADDR.  SIZE is not used.  */
+
+int
+netbsd_process_target::insert_point (enum raw_bkpt_type type, CORE_ADDR addr,
+		     int size, struct raw_breakpoint *bp)
+{
+  switch (type)
+    {
+    case raw_bkpt_type_sw:
+      return insert_memory_breakpoint (bp);
+    case raw_bkpt_type_hw:
+    case raw_bkpt_type_write_wp:
+    case raw_bkpt_type_read_wp:
+    case raw_bkpt_type_access_wp:
+    default:
+      return 1; /* Not supported.  */
+    }
+}
+
+/* Remove {break/watch}point at address ADDR.  SIZE is not used.  */
+
+int
+netbsd_process_target::remove_point (enum raw_bkpt_type type, CORE_ADDR addr,
+				     int size, struct raw_breakpoint *bp)
+{
+  switch (type)
+    {
+    case raw_bkpt_type_sw:
+      return remove_memory_breakpoint (bp);
+    case raw_bkpt_type_hw:
+    case raw_bkpt_type_write_wp:
+    case raw_bkpt_type_read_wp:
+    case raw_bkpt_type_access_wp:
+    default:
+      return 1; /* Not supported.  */
+    }
+}
+
+/* Implement the stopped_by_sw_breakpoint target_ops method.  */
+
+bool
+netbsd_process_target::stopped_by_sw_breakpoint ()
+{
+  ptrace_siginfo_t psi;
+  pid_t pid = current_process ()->pid;
+
+  if (ptrace (PT_GET_SIGINFO, pid, &psi, sizeof (psi)) == -1)
+    perror_with_name (("ptrace"));
+
+  return psi.psi_siginfo.si_signo == SIGTRAP &&
+	 psi.psi_siginfo.si_code == TRAP_BRKPT;
+}
+
+/* Implement the supports_stopped_by_sw_breakpoint target_ops method.  */
+
+bool
+netbsd_process_target::supports_stopped_by_sw_breakpoint ()
+{
+  return true;
+}
+
+/* Implement the supports_qxfer_siginfo target_ops method.  */
+
+bool
+netbsd_process_target::supports_qxfer_siginfo ()
+{
+  return true;
+}
+
+/* Implement the qxfer_siginfo target_ops method.  */
+
+int
+netbsd_process_target::qxfer_siginfo (const char *annex, unsigned char *readbuf,
+				      unsigned const char *writebuf,
+				      CORE_ADDR offset, int len)
+{
+  if (current_thread == nullptr)
+    return -1;
+
+  pid_t pid = current_process ()->pid;
+
+  return netbsd_nat::qxfer_siginfo(pid, annex, readbuf, writebuf, offset, len);
+}
+
+/* Implement the supports_non_stop target_ops method.  */
+
+bool
+netbsd_process_target::supports_non_stop ()
+{
+  return false;
+}
+
+/* Implement the supports_multi_process target_ops method.  */
+
+bool
+netbsd_process_target::supports_multi_process ()
+{
+  return true;
+}
+
+/* Check if fork events are supported.  */
+
+bool
+netbsd_process_target::supports_fork_events ()
+{
+  return false;
+}
+
+/* Check if vfork events are supported.  */
+
+bool
+netbsd_process_target::supports_vfork_events ()
+{
+  return false;
+}
+
+/* Check if exec events are supported.  */
+
+bool
+netbsd_process_target::supports_exec_events ()
+{
+  return true;
+}
+
+/* Implement the supports_disable_randomization target_ops method.  */
+
+bool
+netbsd_process_target::supports_disable_randomization ()
+{
+  return false;
+}
+
+/* Extract &phdr and num_phdr in the inferior.  Return 0 on success.  */
+
+template <typename T>
+int get_phdr_phnum_from_proc_auxv (const pid_t pid,
+				   CORE_ADDR *phdr_memaddr, int *num_phdr)
+{
+  typedef typename std::conditional<sizeof(T) == sizeof(int64_t),
+				    Aux64Info, Aux32Info>::type auxv_type;
+  const size_t auxv_size = sizeof (auxv_type);
+  const size_t auxv_buf_size = 128 * sizeof (auxv_type);
+
+  std::vector<char> auxv_buf;
+  auxv_buf.resize (auxv_buf_size);
+
+  netbsd_read_auxv (pid, nullptr, auxv_buf.data (), auxv_buf_size);
+
+  *phdr_memaddr = 0;
+  *num_phdr = 0;
+
+  for (char *buf = auxv_buf.data ();
+       buf < (auxv_buf.data () + auxv_buf_size);
+       buf += auxv_size)
+    {
+      auxv_type *const aux = (auxv_type *) buf;
+
+      switch (aux->a_type)
+	{
+	case AT_PHDR:
+	  *phdr_memaddr = aux->a_v;
+	  break;
+	case AT_PHNUM:
+	  *num_phdr = aux->a_v;
+	  break;
+	}
+
+      if (*phdr_memaddr != 0 && *num_phdr != 0)
+	break;
+    }
+
+  if (*phdr_memaddr == 0 || *num_phdr == 0)
+    {
+      warning ("Unexpected missing AT_PHDR and/or AT_PHNUM: "
+	       "phdr_memaddr = %s, phdr_num = %d",
+	       core_addr_to_string (*phdr_memaddr), *num_phdr);
+      return 2;
+    }
+
+  return 0;
+}
+
+/* Return &_DYNAMIC (via PT_DYNAMIC) in the inferior, or 0 if not present.  */
+
+template <typename T>
+static CORE_ADDR
+get_dynamic (netbsd_process_target *target, const pid_t pid)
+{
+  typedef typename std::conditional<sizeof(T) == sizeof(int64_t),
+				    Elf64_Phdr, Elf32_Phdr>::type phdr_type;
+  const int phdr_size = sizeof (phdr_type);
+
+  CORE_ADDR phdr_memaddr;
+  int num_phdr;
+  if (get_phdr_phnum_from_proc_auxv<T> (pid, &phdr_memaddr, &num_phdr))
+    return 0;
+
+  std::vector<unsigned char> phdr_buf;
+  phdr_buf.resize (num_phdr * phdr_size);
+
+  if (target->read_memory (phdr_memaddr, phdr_buf.data (), phdr_buf.size ()))
+    return 0;
+
+  /* Compute relocation: it is expected to be 0 for "regular" executables,
+     non-zero for PIE ones.  */
+  CORE_ADDR relocation = -1;
+  for (int i = 0; relocation == -1 && i < num_phdr; i++)
+    {
+      phdr_type *const p = (phdr_type *) (phdr_buf.data() + i * phdr_size);
+
+      if (p->p_type == PT_PHDR)
+	relocation = phdr_memaddr - p->p_vaddr;
+    }
+
+  if (relocation == -1)
+    {
+      /* PT_PHDR is optional, but necessary for PIE in general.  Fortunately
+	 any real world executables, including PIE executables, have always
+	 PT_PHDR present.  PT_PHDR is not present in some shared libraries or
+	 in fpc (Free Pascal 2.4) binaries but neither of those have a need for
+	 or present DT_DEBUG anyway (fpc binaries are statically linked).
+
+	 Therefore if there exists DT_DEBUG there is always also PT_PHDR.
+
+	 GDB could find RELOCATION also from AT_ENTRY - e_entry.  */
+
+      return 0;
+    }
+
+  for (int i = 0; i < num_phdr; i++)
+    {
+      phdr_type *const p = (phdr_type *) (phdr_buf.data () + i * phdr_size);
+
+      if (p->p_type == PT_DYNAMIC)
+	return p->p_vaddr + relocation;
+    }
+
+  return 0;
+}
+
+/* Return &_r_debug in the inferior, or -1 if not present.  Return value
+   can be 0 if the inferior does not yet have the library list initialized.
+   We look for DT_MIPS_RLD_MAP first.  MIPS executables use this instead of
+   DT_DEBUG, although they sometimes contain an unused DT_DEBUG entry too.  */
+
+template <typename T>
+static CORE_ADDR
+get_r_debug (netbsd_process_target *target, const int pid)
+{
+  typedef typename std::conditional<sizeof(T) == sizeof(int64_t),
+				    Elf64_Dyn, Elf32_Dyn>::type dyn_type;
+  const int dyn_size = sizeof (dyn_type);
+  unsigned char buf[sizeof (dyn_type)];  /* The larger of the two.  */
+  CORE_ADDR map = -1;
+
+  CORE_ADDR dynamic_memaddr = get_dynamic<T> (target, pid);
+  if (dynamic_memaddr == 0)
+    return map;
+
+  while (target->read_memory (dynamic_memaddr, buf, dyn_size) == 0)
+    {
+      dyn_type *const dyn = (dyn_type *) buf;
+#if defined DT_MIPS_RLD_MAP
+      union
+      {
+	T map;
+	unsigned char buf[sizeof (T)];
+      }
+      rld_map;
+
+      if (dyn->d_tag == DT_MIPS_RLD_MAP)
+	{
+	  if (read_memory (dyn->d_un.d_val,
+			   rld_map.buf, sizeof (rld_map.buf)) == 0)
+	    return rld_map.map;
+	  else
+	    break;
+	}
+#endif  /* DT_MIPS_RLD_MAP */
+
+      if (dyn->d_tag == DT_DEBUG && map == -1)
+	map = dyn->d_un.d_val;
+
+      if (dyn->d_tag == DT_NULL)
+	break;
+
+      dynamic_memaddr += dyn_size;
+    }
+
+  return map;
+}
+
+/* Read one pointer from MEMADDR in the inferior.  */
+
+static int
+read_one_ptr (netbsd_process_target *target, CORE_ADDR memaddr, CORE_ADDR *ptr,
+	      int ptr_size)
+{
+  /* Go through a union so this works on either big or little endian
+     hosts, when the inferior's pointer size is smaller than the size
+     of CORE_ADDR.  It is assumed the inferior's endianness is the
+     same of the superior's.  */
+
+  union
+  {
+    CORE_ADDR core_addr;
+    unsigned int ui;
+    unsigned char uc;
+  } addr;
+
+  int ret = target->read_memory (memaddr, &addr.uc, ptr_size);
+  if (ret == 0)
+    {
+      if (ptr_size == sizeof (CORE_ADDR))
+	*ptr = addr.core_addr;
+      else if (ptr_size == sizeof (unsigned int))
+	*ptr = addr.ui;
+      else
+	gdb_assert_not_reached ("unhandled pointer size");
+    }
+  return ret;
+}
+
+/* Construct qXfer:libraries-svr4:read reply.  */
+
+template <typename T>
+int
+netbsd_qxfer_libraries_svr4 (netbsd_process_target *target,
+			     const pid_t pid, const char *annex,
+			     unsigned char *readbuf,
+			     unsigned const char *writebuf,
+			     CORE_ADDR offset, int len)
+{
+  struct link_map_offsets
+  {
+    /* Offset and size of r_debug.r_version.  */
+    int r_version_offset;
+
+    /* Offset and size of r_debug.r_map.  */
+    int r_map_offset;
+
+    /* Offset to l_addr field in struct link_map.  */
+    int l_addr_offset;
+
+    /* Offset to l_name field in struct link_map.  */
+    int l_name_offset;
+
+    /* Offset to l_ld field in struct link_map.  */
+    int l_ld_offset;
+
+    /* Offset to l_next field in struct link_map.  */
+    int l_next_offset;
+
+    /* Offset to l_prev field in struct link_map.  */
+    int l_prev_offset;
+  };
+
+  static const struct link_map_offsets lmo_32bit_offsets =
+    {
+      0,     /* r_version offset. */
+      4,     /* r_debug.r_map offset.  */
+      0,     /* l_addr offset in link_map.  */
+      4,     /* l_name offset in link_map.  */
+      8,     /* l_ld offset in link_map.  */
+      12,    /* l_next offset in link_map.  */
+      16     /* l_prev offset in link_map.  */
+    };
+
+  static const struct link_map_offsets lmo_64bit_offsets =
+    {
+      0,     /* r_version offset. */
+      8,     /* r_debug.r_map offset.  */
+      0,     /* l_addr offset in link_map.  */
+      8,     /* l_name offset in link_map.  */
+      16,    /* l_ld offset in link_map.  */
+      24,    /* l_next offset in link_map.  */
+      32     /* l_prev offset in link_map.  */
+    };
+
+  CORE_ADDR lm_addr = 0, lm_prev = 0;
+  CORE_ADDR l_name, l_addr, l_ld, l_next, l_prev;
+  int header_done = 0;
+
+  const struct link_map_offsets *lmo
+    = ((sizeof (T) == sizeof (int64_t))
+       ? &lmo_64bit_offsets : &lmo_32bit_offsets);
+  int ptr_size = sizeof (T);
+
+  while (annex[0] != '\0')
+    {
+      const char *sep = strchr (annex, '=');
+      if (sep == nullptr)
+	break;
+
+      int name_len = sep - annex;
+      CORE_ADDR *addrp;
+      if (name_len == 5 && startswith (annex, "start"))
+	addrp = &lm_addr;
+      else if (name_len == 4 && startswith (annex, "prev"))
+	addrp = &lm_prev;
+      else
+	{
+	  annex = strchr (sep, ';');
+	  if (annex == nullptr)
+	    break;
+	  annex++;
+	  continue;
+	}
+
+      annex = decode_address_to_semicolon (addrp, sep + 1);
+    }
+
+  if (lm_addr == 0)
+    {
+      CORE_ADDR r_debug = get_r_debug<T> (target, pid);
+
+      /* We failed to find DT_DEBUG.  Such situation will not change
+	 for this inferior - do not retry it.  Report it to GDB as
+	 E01, see for the reasons at the GDB solib-svr4.c side.  */
+      if (r_debug == (CORE_ADDR) -1)
+	return -1;
+
+      if (r_debug != 0)
+	{
+	  CORE_ADDR map_offset = r_debug + lmo->r_map_offset;
+	  if (read_one_ptr (target, map_offset, &lm_addr, ptr_size) != 0)
+	    warning ("unable to read r_map from %s",
+		     core_addr_to_string (map_offset));
+	}
+    }
+
+  std::string document = "<library-list-svr4 version=\"1.0\"";
+
+  while (lm_addr
+	 && read_one_ptr (target, lm_addr + lmo->l_name_offset,
+			  &l_name, ptr_size) == 0
+	 && read_one_ptr (target, lm_addr + lmo->l_addr_offset,
+			  &l_addr, ptr_size) == 0
+	 && read_one_ptr (target, lm_addr + lmo->l_ld_offset,
+			  &l_ld, ptr_size) == 0
+	 && read_one_ptr (target, lm_addr + lmo->l_prev_offset,
+			  &l_prev, ptr_size) == 0
+	 && read_one_ptr (target, lm_addr + lmo->l_next_offset,
+			  &l_next, ptr_size) == 0)
+    {
+      if (lm_prev != l_prev)
+	{
+	  warning ("Corrupted shared library list: 0x%lx != 0x%lx",
+		   (long) lm_prev, (long) l_prev);
+	  break;
+	}
+
+      /* Ignore the first entry even if it has valid name as the first entry
+	 corresponds to the main executable.  The first entry should not be
+	 skipped if the dynamic loader was loaded late by a static executable
+	 (see solib-svr4.c parameter ignore_first).  But in such case the main
+	 executable does not have PT_DYNAMIC present and this function already
+	 exited above due to failed get_r_debug.  */
+      if (lm_prev == 0)
+	string_appendf (document, " main-lm=\"0x%lx\"",
+			(unsigned long) lm_addr);
+      else
+	{
+	  unsigned char libname[PATH_MAX];
+
+	  /* Not checking for error because reading may stop before
+	     we've got PATH_MAX worth of characters.  */
+	  libname[0] = '\0';
+	  target->read_memory (l_name, libname, sizeof (libname) - 1);
+	  libname[sizeof (libname) - 1] = '\0';
+	  if (libname[0] != '\0')
+	    {
+	      if (!header_done)
+		{
+		  /* Terminate `<library-list-svr4'.  */
+		  document += '>';
+		  header_done = 1;
+		}
+
+	      string_appendf (document, "<library name=\"");
+	      xml_escape_text_append (&document, (char *) libname);
+	      string_appendf (document, "\" lm=\"0x%lx\" "
+			      "l_addr=\"0x%lx\" l_ld=\"0x%lx\"/>",
+			      (unsigned long) lm_addr, (unsigned long) l_addr,
+			      (unsigned long) l_ld);
+	    }
+	}
+
+      lm_prev = lm_addr;
+      lm_addr = l_next;
+    }
+
+  if (!header_done)
+    {
+      /* Empty list; terminate `<library-list-svr4'.  */
+      document += "/>";
+    }
+  else
+    document += "</library-list-svr4>";
+
+  int document_len = document.length ();
+  if (offset < document_len)
+    document_len -= offset;
+  else
+    document_len = 0;
+  if (len > document_len)
+    len = document_len;
+
+  memcpy (readbuf, document.data () + offset, len);
+
+  return len;
+}
+
+/* Return true if FILE is a 64-bit ELF file,
+   false if the file is not a 64-bit ELF file,
+   and error if the file is not accessible or doesn't exist.  */
+
+static bool
+elf_64_file_p (const char *file)
+{
+  int fd = gdb::handle_eintr<int> (-1, ::open, file, O_RDONLY);
+  if (fd < 0)
+    perror_with_name (("open"));
+
+  Elf64_Ehdr header;
+  ssize_t ret = gdb::handle_eintr<ssize_t> (-1, ::read, fd, &header, sizeof (header));
+  if (ret == -1)
+    perror_with_name (("read"));
+  gdb::handle_eintr<int> (-1, ::close, fd);
+  if (ret != sizeof (header))
+    error ("Cannot read ELF file header: %s", file);
+
+  if (header.e_ident[EI_MAG0] != ELFMAG0
+      || header.e_ident[EI_MAG1] != ELFMAG1
+      || header.e_ident[EI_MAG2] != ELFMAG2
+      || header.e_ident[EI_MAG3] != ELFMAG3)
+    error ("Unrecognized ELF file header: %s", file);
+
+  return header.e_ident[EI_CLASS] == ELFCLASS64;
+}
+
+/* Construct qXfer:libraries-svr4:read reply.  */
+
+int
+netbsd_process_target::qxfer_libraries_svr4 (const char *annex,
+					     unsigned char *readbuf,
+					     unsigned const char *writebuf,
+					     CORE_ADDR offset, int len)
+{
+  if (writebuf != nullptr)
+    return -2;
+  if (readbuf == nullptr)
+    return -1;
+
+  struct process_info *proc = current_process ();
+  pid_t pid = proc->pid;
+  bool is_elf64 = elf_64_file_p (netbsd_nat::pid_to_exec_file (pid));
+
+  if (is_elf64)
+    return netbsd_qxfer_libraries_svr4<int64_t> (this, pid, annex, readbuf,
+						 writebuf, offset, len);
+  else
+    return netbsd_qxfer_libraries_svr4<int32_t> (this, pid, annex, readbuf,
+						 writebuf, offset, len);
+}
+
+/* Implement the supports_qxfer_libraries_svr4 target_ops method.  */
+
+bool
+netbsd_process_target::supports_qxfer_libraries_svr4 ()
+{
+  return true;
+}
+
+/* Return the name of a file that can be opened to get the symbols for
+   the child process identified by PID.  */
+
+char *
+netbsd_process_target::pid_to_exec_file (pid_t pid)
+{
+  return const_cast<char *> (netbsd_nat::pid_to_exec_file (pid));
+}
+
+/* Implementation of the target_ops method "supports_pid_to_exec_file".  */
+
+bool
+netbsd_process_target::supports_pid_to_exec_file ()
+{
+  return true;
+}
+
+/* Implementation of the target_ops method "supports_hardware_single_step".  */
+bool
+netbsd_process_target::supports_hardware_single_step ()
+{
+  return true;
+}
+
+/* Implementation of the target_ops method "sw_breakpoint_from_kind".  */
+
+const gdb_byte *
+netbsd_process_target::sw_breakpoint_from_kind (int kind, int *size)
+{
+  static gdb_byte brkpt[PTRACE_BREAKPOINT_SIZE] = {*PTRACE_BREAKPOINT};
+
+  *size = PTRACE_BREAKPOINT_SIZE;
+
+  return brkpt;
+}
+
+/* Implement the thread_name target_ops method.  */
+
+const char *
+netbsd_process_target::thread_name (ptid_t ptid)
+{
+  return netbsd_nat::thread_name (ptid);
+}
+
+/* Implement the supports_catch_syscall target_ops method.  */
+
+bool
+netbsd_process_target::supports_catch_syscall ()
+{
+  return true;
+}
+
+/* Implement the supports_read_auxv target_ops method.  */
+
+bool
+netbsd_process_target::supports_read_auxv ()
+{
+  return true;
+}
+
+/* The NetBSD target ops object.  */
+
+static netbsd_process_target the_netbsd_target;
+
+void
+initialize_low ()
+{
+  set_target_ops (&the_netbsd_target);
+  the_low_target.arch_setup ();
+}
diff --git a/gdbserver/netbsd-low.h b/gdbserver/netbsd-low.h
new file mode 100644
index 0000000..3d2ec34
--- /dev/null
+++ b/gdbserver/netbsd-low.h
@@ -0,0 +1,154 @@
+/* Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef GDBSERVER_NETBSD_LOW_H
+#define GDBSERVER_NETBSD_LOW_H
+
+struct regcache;
+struct target_desc;
+
+/*  Some information relative to a given register set.   */
+
+struct netbsd_regset_info
+{
+  /* The ptrace request needed to get/set registers of this set.  */
+  int get_request, set_request;
+  /* The size of the register set.  */
+  int size;
+  /* Fill the buffer BUF from the contents of the given REGCACHE.  */
+  void (*fill_function) (struct regcache *regcache, char *buf);
+  /* Store the register value in BUF in the given REGCACHE.  */
+  void (*store_function) (struct regcache *regcache, const char *buf);
+};
+
+/* A list of regsets for the target being debugged, terminated by an entry
+   where the size is negative.
+
+   This list should be created by the target-specific code.  */
+
+extern struct netbsd_regset_info netbsd_target_regsets[];
+
+/* The target-specific operations for NetBSD support.  */
+
+struct netbsd_target_ops
+{
+  /* Architecture-specific setup.  */
+  void (*arch_setup) ();
+};
+
+/* Target ops definitions for a NetBSD target.  */
+
+class netbsd_process_target : public process_stratum_target
+{
+public:
+
+  int create_inferior (const char *program,
+		       const std::vector<char *> &program_args) override;
+
+  void post_create_inferior () override;
+
+  int attach (unsigned long pid) override;
+
+  int kill (process_info *proc) override;
+
+  int detach (process_info *proc) override;
+
+  void mourn (process_info *proc) override;
+
+  void join (int pid) override;
+
+  bool thread_alive (ptid_t pid) override;
+
+  void resume (thread_resume *resume_info, size_t n) override;
+
+  ptid_t wait (ptid_t ptid, target_waitstatus *status,
+	       int options) override;
+
+  void fetch_registers (regcache *regcache, int regno) override;
+
+  void store_registers (regcache *regcache, int regno) override;
+
+  int read_memory (CORE_ADDR memaddr, unsigned char *myaddr,
+		   int len) override;
+
+  int write_memory (CORE_ADDR memaddr, const unsigned char *myaddr,
+		    int len) override;
+
+  void request_interrupt () override;
+
+  bool supports_read_auxv () override;
+
+  int read_auxv (CORE_ADDR offset, unsigned char *myaddr,
+		 unsigned int len) override;
+
+  bool supports_hardware_single_step () override;
+
+  const gdb_byte *sw_breakpoint_from_kind (int kind, int *size) override;
+
+  bool supports_z_point_type (char z_type) override;
+
+  int insert_point (enum raw_bkpt_type type, CORE_ADDR addr,
+		    int size, struct raw_breakpoint *bp) override;
+
+  int remove_point (enum raw_bkpt_type type, CORE_ADDR addr,
+		    int size, struct raw_breakpoint *bp) override;
+
+  bool stopped_by_sw_breakpoint () override;
+
+  bool supports_qxfer_siginfo () override;
+
+  int qxfer_siginfo (const char *annex, unsigned char *readbuf,
+		     unsigned const char *writebuf, CORE_ADDR offset,
+		     int len) override;
+
+  bool supports_stopped_by_sw_breakpoint () override;
+
+  bool supports_non_stop () override;
+
+  bool supports_multi_process () override;
+
+  bool supports_fork_events () override;
+
+  bool supports_vfork_events () override;
+
+  bool supports_exec_events () override;
+
+  bool supports_disable_randomization () override;
+
+  bool supports_qxfer_libraries_svr4 () override;
+
+  int qxfer_libraries_svr4 (const char*, unsigned char*, const unsigned char*,
+			    CORE_ADDR, int) override;
+
+  bool supports_pid_to_exec_file () override;
+
+  char *pid_to_exec_file (int pid) override;
+
+  const char *thread_name (ptid_t thread) override;
+
+  bool supports_catch_syscall () override;
+};
+
+/* The inferior's target description.  This is a global because the
+   NetBSD ports support neither bi-arch nor multi-process.  */
+
+extern struct netbsd_target_ops the_low_target;
+
+/* XXX: multilib */
+extern const struct target_desc *netbsd_tdesc;
+
+#endif /* GDBSERVER_NETBSD_LOW_H */