Implement IPv6 support for GDB/gdbserver

This patch implements IPv6 support for both GDB and gdbserver.  Based
on my research, it is the fourth attempt to do that since 2006.  Since
I used ideas from all of the previous patches, I also added their
authors's names on the ChangeLogs as a way to recognize their
efforts.  For reference sake, you can find the previous attempts at:

  https://sourceware.org/ml/gdb-patches/2006-09/msg00192.html

  https://sourceware.org/ml/gdb-patches/2014-02/msg00248.html

  https://sourceware.org/ml/gdb-patches/2016-02/msg00226.html

The basic idea behind the patch is to start using the new
'getaddrinfo'/'getnameinfo' calls, which are responsible for
translating names and addresses in a protocol-independent way.  This
means that if we ever have a new version of the IP protocol, we won't
need to change the code again (or, at least, won't have to change the
majority of the code).

The function 'getaddrinfo' returns a linked list of possible addresses
to connect to.  Dealing with multiple addresses proved to be a hard
task with the current TCP auto-retry mechanism implemented on
ser-tcp:net_open.  For example, when gdbserver listened only on an
IPv4 socket:

  $ ./gdbserver --once 127.0.0.1:1234 ./a.out

and GDB was instructed to try to connect to both IPv6 and IPv4
sockets:

  $ ./gdb -ex 'target extended-remote localhost:1234' ./a.out

the user would notice a somewhat big delay before GDB was able to
connect to the IPv4 socket.  This happened because GDB was trying to
connect to the IPv6 socket first, and had to wait until the connection
timed out before it tried to connect to the IPv4 socket.

For that reason, I had to rewrite the main loop and implement a new
method for handling multiple connections.  After some discussion,
Pedro and I agreed on the following algorithm:

  1) For each entry returned by 'getaddrinfo', we try to open a socket
  and connect to it.

  2.a) If we have a successful 'connect', we just use that connection.

  2.b) If we don't have a successfull 'connect', but if we've got a
  ECONNREFUSED (meaning the the connection was refused), we keep track
  of this fact by using a flag.

  2.c) If we don't have a successfull 'connect', but if we've got a
  EINPROGRESS (meaning that the connection is in progress), we perform
  a 'select' call on the socket until we have a result (either a
  successful connection, or an error on the socket).

  3) If tcp_auto_retry is true, and we haven't gotten a successful
  connection, and at least one of our attempts failed with
  ECONNREFUSED, then we wait a little bit (i.e., call
  'wait_for_connect'), check to see if there was a
  timeout/interruption (in which case we bail out), and then go back
  to (1).

After multiple tests, I was able to connect without delay on the
scenario described above, and was also able to connect in all other
types of scenarios.

I also implemented some hostname parsing functions (along with their
corresponding unit tests) which are used to help GDB and gdbserver to
parse hostname strings provided by the user.  These new functions are
living inside common/netstuff.[ch].  I've had to do that since IPv6
introduces a new URL scheme, which defines that square brackets can be
used to enclose the host part and differentiate it from the
port (e.g., "[::1]:1234" means "host ::1, port 1234").  I spent some
time thinking about a reasonable way to interpret what the user wants,
and I came up with the following:

  - If the user has provided a prefix that doesn't specify the protocol
    version (i.e., "tcp:" or "udp:"), or if the user has not provided
    any prefix, don't make any assumptions (i.e., assume AF_UNSPEC when
    dealing with 'getaddrinfo') *unless* the host starts with "[" (in
    which case, assume it's an IPv6 host).

  - If the user has provided a prefix that does specify the protocol
    version (i.e., "tcp4:", "tcp6:", "udp4:" or "udp6:"), then respect
    that.

This method doesn't follow strictly what RFC 2732 proposes (that
literal IPv6 addresses should be provided enclosed in "[" and "]")
because IPv6 addresses still can be provided without square brackets
in our case, but since we have prefixes to specify protocol versions I
think this is not an issue.

Another thing worth mentioning is the new 'GDB_TEST_SOCKETHOST'
testcase parameter, which makes it possible to specify the
hostname (without the port) to be used when testing GDB and
gdbserver.  For example, to run IPv6 tests:

  $ make check-gdb RUNTESTFLAGS='GDB_TEST_SOCKETHOST=tcp6:[::1]'

Or, to run IPv4 tests:

  $ make check-gdb RUNTESTFLAGS='GDB_TEST_SOCKETHOST=tcp4:127.0.0.1'

This required a few changes on the gdbserver-base.exp, and also a
minimal adjustment on gdb.server/run-without-local-binary.exp.

Finally, I've implemented a new testcase,
gdb.server/server-connect.exp, which is supposed to run on the native
host and perform various "smoke tests" using different connection
methods.

This patch has been regression-tested on BuildBot and locally, and
also built using a x86_64-w64-mingw32 GCC, and no problems were found.

gdb/ChangeLog:
2018-07-11  Sergio Durigan Junior  <sergiodj@redhat.com>
	    Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Paul Fertser  <fercerpav@gmail.com>
	    Tsutomu Seki  <sekiriki@gmail.com>
	    Pedro Alves  <palves@redhat.com>

	* Makefile.in (SUBDIR_UNITTESTS_SRCS): Add
	'unittests/parse-connection-spec-selftests.c'.
	(COMMON_SFILES): Add 'common/netstuff.c'.
	(HFILES_NO_SRCDIR): Add 'common/netstuff.h'.
	* NEWS (Changes since GDB 8.2): Mention IPv6 support.
	* common/netstuff.c: New file.
	* common/netstuff.h: New file.
	* ser-tcp.c: Include 'netstuff.h' and 'wspiapi.h'.
	(wait_for_connect): Update comment.  New parameter
	'gdb::optional<int> sock' instead of 'struct serial *scb'.
	Use 'sock' directly instead of 'scb->fd'.
	(try_connect): New function, with code from 'net_open'.
	(net_open): Rewrite main loop to deal with multiple
	sockets/addresses.  Handle IPv6-style hostnames; implement
	support for IPv6 connections.
	* unittests/parse-connection-spec-selftests.c: New file.

gdb/gdbserver/ChangeLog:
2018-07-11  Sergio Durigan Junior  <sergiodj@redhat.com>
	    Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Paul Fertser  <fercerpav@gmail.com>
	    Tsutomu Seki  <sekiriki@gmail.com>

	* Makefile.in (SFILES): Add '$(srcdir)/common/netstuff.c'.
	(OBS): Add 'common/netstuff.o'.
	(GDBREPLAY_OBS): Likewise.
	* gdbreplay.c: Include 'wspiapi.h' and 'netstuff.h'.
	(remote_open): Implement support for IPv6
	connections.
	* remote-utils.c: Include 'netstuff.h', 'filestuff.h'
	and 'wspiapi.h'.
	(handle_accept_event): Accept connections from IPv6 sources.
	(remote_prepare): Handle IPv6-style hostnames; implement
	support for IPv6 connections.
	(remote_open): Implement support for printing connections from
	IPv6 sources.

gdb/testsuite/ChangeLog:
2018-07-11  Sergio Durigan Junior  <sergiodj@redhat.com>
	    Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Paul Fertser  <fercerpav@gmail.com>
	    Tsutomu Seki  <sekiriki@gmail.com>

	* README (Testsuite Parameters): Mention new 'GDB_TEST_SOCKETHOST'
	parameter.
	* boards/native-extended-gdbserver.exp: Do not set 'sockethost'
	by default.
	* boards/native-gdbserver.exp: Likewise.
	* gdb.server/run-without-local-binary.exp: Improve regexp used
	for detecting when a remote debugging connection succeeds.
	* gdb.server/server-connect.exp: New file.
	* lib/gdbserver-support.exp (gdbserver_default_get_comm_port):
	Do not prefix the port number with ":".
	(gdbserver_start): New global GDB_TEST_SOCKETHOST.  Implement
	support for detecting and using it.  Add '$debughost_gdbserver'
	to the list of arguments used to start gdbserver.  Handle case
	when gdbserver cannot resolve a network name.

gdb/doc/ChangeLog:
2018-07-11  Sergio Durigan Junior  <sergiodj@redhat.com>
	    Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Paul Fertser  <fercerpav@gmail.com>
	    Tsutomu Seki  <sekiriki@gmail.com>

	* gdb.texinfo (Remote Connection Commands): Add explanation
	about new IPv6 support.  Add new connection prefixes.

2 files changed, 231 insertions, 0 deletions

diff --git a/gdb/common/netstuff.c b/gdb/common/netstuff.c
new file mode 100644
index 0000000..c1c401c
--- /dev/null
+++ b/gdb/common/netstuff.c
@@ -0,0 +1,155 @@
+/* Operations on network stuff.
+   Copyright (C) 2018 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 "common-defs.h"
+#include "netstuff.h"
+#include <algorithm>
+
+#ifdef USE_WIN32API
+#include <winsock2.h>
+#include <wspiapi.h>
+#else
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <sys/socket.h>
+#include <netinet/tcp.h>
+#endif
+
+/* See common/netstuff.h.  */
+
+scoped_free_addrinfo::~scoped_free_addrinfo ()
+{
+  freeaddrinfo (m_res);
+}
+
+/* See common/netstuff.h.  */
+
+parsed_connection_spec
+parse_connection_spec_without_prefix (std::string spec, struct addrinfo *hint)
+{
+  parsed_connection_spec ret;
+  size_t last_colon_pos = 0;
+  /* We're dealing with IPv6 if:
+
+     - ai_family is AF_INET6, or
+     - ai_family is not AF_INET, and
+       - spec[0] is '[', or
+       - the number of ':' on spec is greater than 1.  */
+  bool is_ipv6 = (hint->ai_family == AF_INET6
+		  || (hint->ai_family != AF_INET
+		      && (spec[0] == '['
+			  || std::count (spec.begin (),
+					 spec.end (), ':') > 1)));
+
+  if (is_ipv6)
+    {
+      if (spec[0] == '[')
+	{
+	  /* IPv6 addresses can be written as '[ADDR]:PORT', and we
+	     support this notation.  */
+	  size_t close_bracket_pos = spec.find_first_of (']');
+
+	  if (close_bracket_pos == std::string::npos)
+	    error (_("Missing close bracket in hostname '%s'"),
+		   spec.c_str ());
+
+	  hint->ai_family = AF_INET6;
+
+	  const char c = spec[close_bracket_pos + 1];
+
+	  if (c == '\0')
+	    last_colon_pos = std::string::npos;
+	  else if (c != ':')
+	    error (_("Invalid cruft after close bracket in '%s'"),
+		   spec.c_str ());
+
+	  /* Erase both '[' and ']'.  */
+	  spec.erase (0, 1);
+	  spec.erase (close_bracket_pos - 1, 1);
+	}
+      else if (spec.find_first_of (']') != std::string::npos)
+	error (_("Missing open bracket in hostname '%s'"),
+	       spec.c_str ());
+    }
+
+  if (last_colon_pos == 0)
+    last_colon_pos = spec.find_last_of (':');
+
+  /* The length of the hostname part.  */
+  size_t host_len;
+
+  if (last_colon_pos != std::string::npos)
+    {
+      /* The user has provided a port.  */
+      host_len = last_colon_pos;
+      ret.port_str = spec.substr (last_colon_pos + 1);
+    }
+  else
+    host_len = spec.size ();
+
+  ret.host_str = spec.substr (0, host_len);
+
+  /* Default hostname is localhost.  */
+  if (ret.host_str.empty ())
+    ret.host_str = "localhost";
+
+  return ret;
+}
+
+/* See common/netstuff.h.  */
+
+parsed_connection_spec
+parse_connection_spec (const char *spec, struct addrinfo *hint)
+{
+  /* Struct to hold the association between valid prefixes, their
+     family and socktype.  */
+  struct host_prefix
+    {
+      /* The prefix.  */
+      const char *prefix;
+
+      /* The 'ai_family'.  */
+      int family;
+
+      /* The 'ai_socktype'.  */
+      int socktype;
+    };
+  static const struct host_prefix prefixes[] =
+    {
+      { "udp:",  AF_UNSPEC, SOCK_DGRAM },
+      { "tcp:",  AF_UNSPEC, SOCK_STREAM },
+      { "udp4:", AF_INET,   SOCK_DGRAM },
+      { "tcp4:", AF_INET,   SOCK_STREAM },
+      { "udp6:", AF_INET6,  SOCK_DGRAM },
+      { "tcp6:", AF_INET6,  SOCK_STREAM },
+    };
+
+  for (const host_prefix prefix : prefixes)
+    if (startswith (spec, prefix.prefix))
+      {
+	spec += strlen (prefix.prefix);
+	hint->ai_family = prefix.family;
+	hint->ai_socktype = prefix.socktype;
+	hint->ai_protocol
+	  = hint->ai_socktype == SOCK_DGRAM ? IPPROTO_UDP : IPPROTO_TCP;
+	break;
+      }
+
+  return parse_connection_spec_without_prefix (spec, hint);
+}
diff --git a/gdb/common/netstuff.h b/gdb/common/netstuff.h
new file mode 100644
index 0000000..2b65807
--- /dev/null
+++ b/gdb/common/netstuff.h
@@ -0,0 +1,76 @@
+/* Operations on network stuff.
+   Copyright (C) 2018 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 NETSTUFF_H
+#define NETSTUFF_H
+
+#include <string>
+
+/* Like NI_MAXHOST/NI_MAXSERV, but enough for numeric forms.  */
+#define GDB_NI_MAX_ADDR 64
+#define GDB_NI_MAX_PORT 16
+
+/* Helper class to guarantee that we always call 'freeaddrinfo'.  */
+
+class scoped_free_addrinfo
+{
+public:
+  /* Default constructor.  */
+  explicit scoped_free_addrinfo (struct addrinfo *ainfo)
+    : m_res (ainfo)
+  {
+  }
+
+  /* Destructor responsible for free'ing M_RES by calling
+     'freeaddrinfo'.  */
+  ~scoped_free_addrinfo ();
+
+  DISABLE_COPY_AND_ASSIGN (scoped_free_addrinfo);
+
+private:
+  /* The addrinfo resource.  */
+  struct addrinfo *m_res;
+};
+
+/* The struct we return after parsing the connection spec.  */
+
+struct parsed_connection_spec
+{
+  /* The hostname.  */
+  std::string host_str;
+
+  /* The port, if any.  */
+  std::string port_str;
+};
+
+
+/* Parse SPEC (which is a string in the form of "ADDR:PORT") and
+   return a 'parsed_connection_spec' structure with the proper fields
+   filled in.  Also adjust HINT accordingly.  */
+extern parsed_connection_spec
+  parse_connection_spec_without_prefix (std::string spec,
+					struct addrinfo *hint);
+
+/* Parse SPEC (which is a string in the form of
+   "[tcp[6]:|udp[6]:]ADDR:PORT") and return a 'parsed_connection_spec'
+   structure with the proper fields filled in.  Also adjust HINT
+   accordingly.  */
+extern parsed_connection_spec parse_connection_spec (const char *spec,
+						     struct addrinfo *hint);
+
+#endif /* ! NETSTUFF_H */