Re: [PATCH 10/10] Add minimal and functional NetBSD/amd64 gdbserver

[Kamil Rytarowski <kamil@netbsd.org>]

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On 03.09.2020 19:42, Aktemur, Tankut Baris wrote:
> On September 2, 2020 7:59 PM, Kamil Rytarowski wrote:
>> 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.
>>
>> gdb/ChangeLog:
> 
> This should be gdbserver/ChangeLog.
> 

Fixed.

>>
>>        * netbsd-low.cc: Add.
>>        * netbsd-low.h: Likewise.
>>        * netbsd-x86_64-low.cc: Likewise.
>>        * Makefile.in (SFILES): Register "netbsd-low.cc", "netbsd-low.h",
>>        "netbsd-x86_64-low.cc".
>>        * configure.srv: Add x86_64-*-netbsd*.
>> ---
>>  gdbserver/ChangeLog            |    9 +
>>  gdbserver/Makefile.in          |    3 +
>>  gdbserver/configure.srv        |    7 +
>>  gdbserver/netbsd-low.cc        | 1352 ++++++++++++++++++++++++++++++++
>>  gdbserver/netbsd-low.h         |  157 ++++
>>  gdbserver/netbsd-x86_64-low.cc |  250 ++++++
>>  6 files changed, 1778 insertions(+)
>>  create mode 100644 gdbserver/netbsd-low.cc
>>  create mode 100644 gdbserver/netbsd-low.h
>>  create mode 100644 gdbserver/netbsd-x86_64-low.cc
>>
>> diff --git a/gdbserver/ChangeLog b/gdbserver/ChangeLog
>> index e437493b56d..c0732d1a28a 100644
>> --- a/gdbserver/ChangeLog
>> +++ b/gdbserver/ChangeLog
>> @@ -1,3 +1,12 @@
>> +2020-08-13  Kamil Rytarowski  <n54@gmx.com>
>> +
>> +	* netbsd-low.cc: Add.
>> +	* netbsd-low.h: Likewise.
>> +	* netbsd-x86_64-low.cc: Likewise.
>> +	* Makefile.in (SFILES): Register "netbsd-low.cc", "netbsd-low.h",
>> +	"netbsd-x86_64-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 9d7687be534..1d597b14523 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-low.cc \
>> +	$(srcdir)/netbsd-low.h \
>> +	$(srcdir)/netbsd-x86_64-low.cc \
>>  	$(srcdir)/proc-service.cc \
>>  	$(srcdir)/proc-service.list \
>>  	$(srcdir)/regcache.cc \
>> diff --git a/gdbserver/configure.srv b/gdbserver/configure.srv
>> index 5e33bd9c54d..12f9d410b7c 100644
>> --- a/gdbserver/configure.srv
>> +++ b/gdbserver/configure.srv
>> @@ -349,6 +349,13 @@ case "${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-x86_64-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"
>> +			srv_netbsd=yes
> 
> Is `srv_netbsd` used anywhere?
> 

Not used. I have removed it.

Other targets use it in configure.ac and this is not needed for NetBDS.

>> +			;;
>>
>>    xtensa*-*-linux*)	srv_regobj=reg-xtensa.o
>>  			srv_tgtobj="$srv_linux_obj linux-xtensa-low.o"
>> diff --git a/gdbserver/netbsd-low.cc b/gdbserver/netbsd-low.cc
>> new file mode 100644
>> index 00000000000..db9531c66d3
>> --- /dev/null
>> +++ b/gdbserver/netbsd-low.cc
>> @@ -0,0 +1,1352 @@
>> +/* 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 initializes
> 
> To be consistent with the imperative "Call", "initializes" could read
> "initialize".
> 

Fixed.

>> +   the process' private data.  */
>> +
>> +static struct process_info *
>> +netbsd_add_process (int pid, int attached)
> 
> There are two uses of this function and in both the return value is ignored.
> The function could as well be void.
> 

Done.

>> +{
>> +  struct process_info *proc = add_process (pid, attached);
>> +  proc->tdesc = netbsd_tdesc;
>> +  proc->priv = nullptr;
>> +
>> +  return proc;
>> +}
>> +
>> +/* 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.  */;
> 
> Any particular reason for the explicit ';'?
> 

Copied from Linux. I've removed the strat semicolon.

gdbserver/linux-low.cc:   /* Errors ignored.  */;

>> +	}
>> +    }
>> +}
>> +
>> +/* Register threads in the process specified by PID.  */
>> +
>> +static void
>> +netbsd_add_threads (pid_t pid)
>> +{
>> +  auto fn
>> +    = [] (ptid_t ptid)
>> +      {
>> +	add_thread (ptid, nullptr);
>> +      };
>> +
>> +  netbsd_nat::list_threads (pid, fn);
> 
> IMHO, the name "list_threads" gives the impression that it only lists the threads
> and is side-effect free.  Maybe use something like "for_each_thread", as in gdbthread.h?
> 

I've renamed it to for_each_thread.

>> +}
>> +
>> +/* 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)
>> +{
>> +
>> +  if (ptrace (PT_ATTACH, pid, nullptr, 0) != 0)
>> +    error ("Cannot attach to process %lu: %s (%d)\n", pid,
>> +	    safe_strerror (errno), errno);
>> +
>> +  netbsd_add_process (pid, 1);
>> +  netbsd_nat::enable_proc_events (pid);
>> +  netbsd_add_threads (pid);
>> +
>> +  return 0;
>> +}
>> +
>> +/* 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::list_threads (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.  */
> 
> A blank line here between the comment and the function header.
> 

Fixed.

>> +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 (::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..  */
> 
> Double periods.
> 

Fixed.

>> +  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 */
> 
> End with dot-space-space?
> 

Fixed.

>> +  ptrace_state_t pst = {};
>> +  if (code == TRAP_LWP)
>> +    {
>> +      if (ptrace (PT_GET_PROCESS_STATE, pid, &pst, sizeof (pst)) == -1)
>> +	perror_with_name (("ptrace"));
>> +    }
> 
> I think braces can be removed.
> 

Fixed.

>> +
>> +  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;
>> +    }
> 
> Braces can be removed.
> 

Fixed.

>> +
>> +  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 =
> 
> The assignment operator should be on the next line.
> 

Fixed and added () for nicer alignment.

>> +	(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. */
> 
> Dot-space-space.
> 

Fixed.

>> +      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 (("Unknwon stopped status"));
> 
> Typo "Unknwon".
> 

Fixed.

>> +	}
>> +    }
>> +}
>> +
>> +/* Implement the kill target_ops method.  */
>> +
>> +int
>> +netbsd_process_target::kill (process_info *process)
>> +{
>> +  pid_t pid = process->pid;
>> +  ptrace (PT_KILL, pid, nullptr, 0);
>> +
>> +  int status;
>> +  gdb::handle_eintr (::waitpid, pid, &status, 0);
> 
> The "kill" target op is supposed to return -1 on failure.
> So, maybe not ignore the return value of handle_eintr here?
> 

Fixed. I've added an error check for ptrace(2) and waitpid(2).

>> +  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)
>> +    {
>> +      char *buf = (char *) xmalloc (regset->size);
>> +      int res = ptrace (regset->get_request, inferior_ptid.pid (), buf,
>> +			inferior_ptid.lwp ());
>> +      if (res == -1)
>> +	perror_with_name (("ptrace"));
>> +      regset->store_function (regcache, buf);
>> +      free (buf);
>> +      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)
>> +    {
>> +      char *buf = (char *)xmalloc (regset->size);
>> +      int res = ptrace (regset->get_request, inferior_ptid.pid (), buf,
>> +			inferior_ptid.lwp ());
>> +      if (res == -1)
>> +	perror_with_name (("ptrace"));
>> +      if (res == 0)
>> +	{
>> +	  /* Then overlay our cached registers on that.  */
>> +	  regset->fill_function (regcache, buf);
>> +	  /* Only now do we write the register set.  */
>> +	  res = ptrace (regset->set_request, inferior_ptid.pid (), buf,
>> +			inferior_ptid.lwp ());
>> +	}
>> +      free (buf);
>> +      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 kill_request target_ops method.  */
> 
> "kill_request" -> "request_interrupt".
> 

Fixed.

>> +
>> +void
>> +netbsd_process_target::request_interrupt ()
>> +{
>> +  ptid_t inferior_ptid = ptid_of (get_first_thread ());
>> +
>> +  ::kill (inferior_ptid.pid(), SIGINT);
>> +}
>> +
> 
> I think a function comment is needed here.
> 

Fixed.

>> +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 to_stopped_by_sw_breakpoint target_ops
>> +   method.  */
> 
> "to_stopped_by_sw_breakpoint" -> "stopped_by_sw_breakpoint".
> 

Fixed.

>> +
>> +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 to_supports_stopped_by_sw_breakpoint target_ops
>> +   method.  */
> 
> The "to_" prefix shall be removed here, too.
> 

Fixed.

>> +
>> +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;
>> +}
> 
> Some of the target ops above do not change the base class behavior.  The override
> can be omitted for code simplicity.  I think it's also OK to retain them if you want
> to make the definitions explicit.
> 

Most of the can be supported in future, except
supports_disable_randomization and supports_non_stop.

I will leave them around for the time being.

>> +
>> +/* 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);
>> +
>> +  char *auxv_buf = (char *) xmalloc (auxv_buf_size);
>> +
>> +  netbsd_read_auxv (pid, nullptr, auxv_buf, auxv_buf_size);
>> +
>> +  *phdr_memaddr = 0;
>> +  *num_phdr = 0;
>> +
>> +  for (char *buf = auxv_buf; buf < (auxv_buf + 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;
>> +    }
>> +
>> +  xfree (auxv_buf);
>> +
>> +  if (*phdr_memaddr == 0 || *num_phdr == 0)
>> +    {
>> +      warning ("Unexpected missing AT_PHDR and/or AT_PHNUM: "
>> +	       "phdr_memaddr = %ld, phdr_num = %d",
>> +	       (long) *phdr_memaddr, *num_phdr);
> 
> It might be better to use `core_addr_to_string` or `core_addr_to_string_nz`
> to print phdr_memaddr.
> 

Fixed. I've picked core_addr_to_string ().

>> +      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 ()))
> 
> Why not simply `target->read_memory`?

Fixed.

> Also, it might be better to explicitly check != 0.
> 

I've avoided it as the line is too long and would need to be wrapped.

>> +    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)
> 
> The `target->read_memory` comment here, too.
> 

Fixed.

>> +    {
>> +      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);
> 
> Here, too.
> 

Fixed.

>> +  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;
> 
> An extra pair of parens can be used to better align '?'.  Like this:
> 
>   const struct link_map_offsets *lmo
>     = ((sizeof (T) == sizeof (int64_t))
>        ? &lmo_64bit_offsets : &lmo_32bit_offsets);
> 

Fixed.

>> +  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)
>> +	{
>> +	  if (read_one_ptr (target, r_debug + lmo->r_map_offset,
>> +			    &lm_addr, ptr_size) != 0)
>> +	    {
>> +	      warning ("unable to read r_map from 0x%lx",
>> +		       (long) r_debug + lmo->r_map_offset);
> 
> Again, `core_addr_to_string` could be used.
> 

Fixed and I've refactored this code into:
+         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));

>> +	    }
>> +	}
> 
> Braces can be removed in both conditional statements above.  And, if you prefer,
> the conditions can be merged via &&.
> 

Fixed.

>> +    }
>> +
>> +  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 (::open, file, O_RDONLY);
>> +  if (fd < 0)
>> +    perror_with_name (("open"));
>> +
>> +  Elf64_Ehdr header;
>> +  ssize_t ret = gdb::handle_eintr (::read, fd, &header, sizeof (header));
>> +  if (ret == -1)
>> +    perror_with_name (("read"));
>> +  gdb::handle_eintr (::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 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];
>> +
>> +  *size = PTRACE_BREAKPOINT_SIZE;
>> +
>> +  memcpy (brkpt, PTRACE_BREAKPOINT, PTRACE_BREAKPOINT_SIZE);
> 
> Is there a need to memcpy each time the function is called?
> 

I've optimized it to remove memcpy(3).

>> +
>> +  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 00000000000..2bd57c51726
>> --- /dev/null
>> +++ b/gdbserver/netbsd-low.h
>> @@ -0,0 +1,157 @@
>> +/* 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);
> 
> Leaving one blank line between each field may improve readability.
> 

Fixed.

>> +};
>> +
>> +/* 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) ();
>> +
>> +  /* Hook to support target specific qSupported.  */
>> +  void (*process_qsupported) (char **, int count);
> 
> Is the `process_qsupported` function called anywhere?
> 

Hmm... it was originally copied from Linux (before C++ification). It
looks like unused now, at least I'm not triggering a call for it.

Should I drop it?

>> +};
> 
> No strong opinion, but the low target could be a derived class of
> netbsd_process_target, like the linux low targets.
> 

This is a simplified x86_64 support and for the time being I will leave
it as it is. During addition of i386, I will switch it to more
linux-like approach.

>> +
>> +/* 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.  */
> 
> The "nor multi-process" part of this comment is confusing.  What does the multi-process
> feature have to do with the_low_target?  And netbsd_process_target was defined to
> support multi-process above in the .cc file.
> 

It was an old comment and I have updated it.

>> +
>> +extern struct netbsd_target_ops the_low_target;
>> +
>> +/* XXX: multilib */
>> +extern const struct target_desc *netbsd_tdesc;
>> +
>> +#endif /* GDBSERVER_NETBSD_LOW_H */
>> diff --git a/gdbserver/netbsd-x86_64-low.cc b/gdbserver/netbsd-x86_64-low.cc
>> new file mode 100644
>> index 00000000000..c8679d9f153
>> --- /dev/null
>> +++ b/gdbserver/netbsd-x86_64-low.cc
>> @@ -0,0 +1,250 @@
>> +/* 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"
>> +
>> +static int use_xml;
>> +
>> +/* 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;
> 
> Space after ')'.
> 

Fixed.

>> +
>> +#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;
> 
> Space after ')'.
> 

Fixed.

>> +
>> +#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;
>> +}
>> +
>> +/* Update all the target description of all processes; a new GDB
>> +   connected, and it may or not support xml target descriptions.  */
>> +
>> +static void
>> +x86_64_netbsd_update_xmltarget (void)
>> +{
>> +  struct thread_info *saved_thread = current_thread;
>> +
>> +  /* Before changing the register cache's internal layout, flush the
>> +     contents of the current valid caches back to the threads, and
>> +     release the current regcache objects.  */
>> +  regcache_release ();
>> +
>> +  for_each_process ([] (process_info *proc) {
>> +		      int pid = proc->pid;
>> +
>> +		      /* Look up any thread of this process.  */
>> +		      current_thread = find_any_thread_of_pid (pid);
>> +
>> +		      the_low_target.arch_setup ();
> 
> I find this confusing because the target object is supposed to be a singleton.
> Why is its arch_setup called for each process?
> 

This logic was copied from Linux, should I drop it? However.. after
removal of process_qsupported this is no longer in use and I have
removed the x86_64_netbsd_update_xmltarget function entirely.

>> +		    });
>> +
>> +  current_thread = saved_thread;
>> +}
>> +
>> +/* Process qSupported query, "xmlRegisters=". */
>> +
>> +static void
>> +netbsd_x86_64_process_qsupported (char **features, int count)
>> +{
>> +  /* Return if gdb doesn't support XML.  If gdb sends "xmlRegisters="
>> +     with "i386" in qSupported query, it supports x86 XML target
>> +     descriptions.  */
>> +  use_xml = 0;
>> +  for (int i = 0; i < count; i++)
>> +    {
>> +      const char *feature = features[i];
>> +
>> +      if (startswith (feature, "xmlRegisters="))
>> +	{
>> +	  char *copy = xstrdup (feature + 13);
>> +	  char *last;
>> +	  char *p;
>> +
>> +	  for (p = strtok_r (copy, ",", &last); p != NULL;
>> +	       p = strtok_r (NULL, ",", &last))
>> +	    {
>> +	      if (strcmp (p, "i386") == 0)
>> +		{
>> +		  use_xml = 1;
>> +		  break;
>> +		}
>> +	    }
>> +
>> +	  free (copy);
>> +	}
>> +    }
>> +  x86_64_netbsd_update_xmltarget ();
>> +}
>> +
>> +/* 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,
>> + netbsd_x86_64_process_qsupported,
>> +};
>> --
>> 2.28.0
> 
> Regards
> -Baris
> 
> 
> Intel Deutschland GmbH
> Registered Address: Am Campeon 10-12, 85579 Neubiberg, Germany
> Tel: +49 89 99 8853-0, www.intel.de
> Managing Directors: Christin Eisenschmid, Gary Kershaw
> Chairperson of the Supervisory Board: Nicole Lau
> Registered Office: Munich
> Commercial Register: Amtsgericht Muenchen HRB 186928
> 



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