Implement the ability to set/unset environment variables to GDBserver when starting the inferior

This patch implements the ability to set/unset environment variables
on the remote target, mimicking what GDB already offers to the user.
There are two features present here: user-set and user-unset
environment variables.

User-set environment variables are only the variables that are
explicitly set by the user, using the 'set environment' command.  This
means that variables that were already present in the environment when
starting GDB/GDBserver are not transmitted/considered by this feature.

User-unset environment variables are variables that are explicitly
unset by the user, using the 'unset environment' command.

The idea behind this patch is to store user-set and user-unset
environment variables in two separate sets, both part of gdb_environ.
Then, when extended_remote_create_inferior is preparing to start the
inferior, it will iterate over the two sets and set/unset variables
accordingly.  Three new packets are introduced:

- QEnvironmentHexEncoded, which is used to set environment variables,
  and contains an hex-encoded string in the format "VAR=VALUE" (VALUE
  can be empty if the user set a variable with a null value, by doing
  'set environment VAR=').

- QEnvironmentUnset, which is used to unset environment variables, and
  contains an hex-encoded string in the format "VAR".

- QEnvironmentReset, which is always the first packet to be
  transmitted, and is used to reset the environment, i.e., discard any
  changes made by the user on previous runs.

The QEnvironmentHexEncoded packet is inspired on LLDB's extensions to
the RSP.  Details about it can be seen here:

  <https://raw.githubusercontent.com/llvm-mirror/lldb/master/docs/lldb-gdb-remote.txt>

I decided not to implement the QEnvironment packet because it is
considered deprecated by LLDB.  This packet, on LLDB, serves the same
purpose of QEnvironmentHexEncoded, but sends the information using a
plain text, non-hex-encoded string.

The other two packets are new.

This patch also includes updates to the documentation, testsuite, and
unit tests, without introducing regressions.

gdb/ChangeLog:
2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	* NEWS (Changes since GDB 8.0): Add entry mentioning new support
	for setting/unsetting environment variables on the remote target.
	(New remote packets): Add entries for QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset.
	* common/environ.c (gdb_environ::operator=): Extend method to
	handle m_user_set_env_list and m_user_unset_env_list.
	(gdb_environ::clear): Likewise.
	(match_var_in_string): Change type of first parameter from 'char
	*' to 'const char *'.
	(gdb_environ::set): Extend method to handle
	m_user_set_env_list and m_user_unset_env_list.
	(gdb_environ::unset): Likewise.
	(gdb_environ::clear_user_set_env): New method.
	(gdb_environ::user_set_envp): Likewise.
	(gdb_environ::user_unset_envp): Likewise.
	* common/environ.h (gdb_environ): Handle m_user_set_env_list and
	m_user_unset_env_list on move constructor/assignment.
	(unset): Add new default parameter 'update_unset_list = true'.
	(clear_user_set_env): New method.
	(user_set_envp): Likewise.
	(user_unset_envp): Likewise.
	(m_user_set_env_list): New std::set.
	(m_user_unset_env_list): Likewise.
	* common/rsp-low.c (hex2str): New function.
	(bin2hex): New overload for bin2hex function.
	* common/rsp-low.c (hex2str): New prototype.
	(str2hex): New overload prototype.
	* remote.c: Include "environ.h". Add QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset.
	(remote_protocol_features): Add QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset packets.
	(send_environment_packet): New function.
	(extended_remote_environment_support): Likewise.
	(extended_remote_create_inferior): Call
	extended_remote_environment_support.
	(_initialize_remote): Add QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset packet configs.
	* unittests/environ-selftests.c (gdb_selftest_env_var):
	New variable.
	(test_vector_initialization): New function.
	(test_init_from_host_environ): Likewise.
	(test_reinit_from_host_environ): Likewise.
	(test_set_A_unset_B_unset_A_cannot_find_A_can_find_B):
	Likewise.
	(test_unset_set_empty_vector): Likewise.
	(test_vector_clear): Likewise.
	(test_std_move): Likewise.
	(test_move_constructor):
	(test_self_move): Likewise.
	(test_set_unset_reset): Likewise.
	(run_tests): Rewrite in terms of the functions above.

gdb/gdbserver/ChangeLog:
2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	* server.c (handle_general_set): Handle QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset packets.
	(handle_query): Inform remote that QEnvironmentHexEncoded,
	QEnvironmentUnset and QEnvironmentReset are supported.

gdb/doc/ChangeLog:
2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.texinfo (set environment): Add @anchor.  Explain that
	environment variables set by the user are sent to GDBserver.
	(unset environment): Likewise, but for unsetting variables.
	(Connecting) <Remote Packet>: Add "environment-hex-encoded",
	"QEnvironmentHexEncoded", "environment-unset", "QEnvironmentUnset",
	"environment-reset" and "QEnvironmentReset" to the table.
	(Remote Protocol) <QEnvironmentHexEncoded, QEnvironmentUnset,
	QEnvironmentReset>: New item, explaining the packet.

gdb/testsuite/ChangeLog:
2017-08-31  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.base/share-env-with-gdbserver.c: New file.
	* gdb.base/share-env-with-gdbserver.exp: Likewise.

4 files changed, 133 insertions, 15 deletions

diff --git a/gdb/common/environ.c b/gdb/common/environ.c
index 698bda3..7753f6e 100644
--- a/gdb/common/environ.c
+++ b/gdb/common/environ.c
@@ -30,8 +30,12 @@ gdb_environ::operator= (gdb_environ &&e)
     return *this;
 
   m_environ_vector = std::move (e.m_environ_vector);
+  m_user_set_env = std::move (e.m_user_set_env);
+  m_user_unset_env = std::move (e.m_user_unset_env);
   e.m_environ_vector.clear ();
   e.m_environ_vector.push_back (NULL);
+  e.m_user_set_env.clear ();
+  e.m_user_unset_env.clear ();
   return *this;
 }
 
@@ -65,6 +69,8 @@ gdb_environ::clear ()
   m_environ_vector.clear ();
   /* Always add the NULL element.  */
   m_environ_vector.push_back (NULL);
+  m_user_set_env.clear ();
+  m_user_unset_env.clear ();
 }
 
 /* Helper function to check if STRING contains an environment variable
@@ -72,7 +78,7 @@ gdb_environ::clear ()
    if it contains, false otherwise.  */
 
 static bool
-match_var_in_string (char *string, const char *var, size_t var_len)
+match_var_in_string (const char *string, const char *var, size_t var_len)
 {
   if (strncmp (string, var, var_len) == 0 && string[var_len] == '=')
     return true;
@@ -99,32 +105,59 @@ gdb_environ::get (const char *var) const
 void
 gdb_environ::set (const char *var, const char *value)
 {
+  char *fullvar = concat (var, "=", value, NULL);
+
   /* We have to unset the variable in the vector if it exists.  */
-  unset (var);
+  unset (var, false);
 
   /* Insert the element before the last one, which is always NULL.  */
-  m_environ_vector.insert (m_environ_vector.end () - 1,
-			   concat (var, "=", value, NULL));
+  m_environ_vector.insert (m_environ_vector.end () - 1, fullvar);
+
+  /* Mark this environment variable as having been set by the user.
+     This will be useful when we deal with setting environment
+     variables on the remote target.  */
+  m_user_set_env.insert (std::string (fullvar));
+
+  /* If this environment variable is marked as unset by the user, then
+     remove it from the list, because now the user wants to set
+     it.  */
+  m_user_unset_env.erase (std::string (var));
 }
 
 /* See common/environ.h.  */
 
 void
-gdb_environ::unset (const char *var)
+gdb_environ::unset (const char *var, bool update_unset_list)
 {
   size_t len = strlen (var);
+  std::vector<char *>::iterator it_env;
 
   /* We iterate until '.end () - 1' because the last element is
      always NULL.  */
-  for (std::vector<char *>::iterator el = m_environ_vector.begin ();
-       el != m_environ_vector.end () - 1;
-       ++el)
-    if (match_var_in_string (*el, var, len))
-      {
-	xfree (*el);
-	m_environ_vector.erase (el);
-	break;
-      }
+  for (it_env = m_environ_vector.begin ();
+       it_env != m_environ_vector.end () - 1;
+       ++it_env)
+    if (match_var_in_string (*it_env, var, len))
+      break;
+
+  if (it_env != m_environ_vector.end () - 1)
+    {
+      m_user_set_env.erase (std::string (*it_env));
+      xfree (*it_env);
+
+      m_environ_vector.erase (it_env);
+    }
+
+  if (update_unset_list)
+    m_user_unset_env.insert (std::string (var));
+}
+
+/* See common/environ.h.  */
+
+void
+gdb_environ::unset (const char *var)
+{
+  unset (var, true);
 }
 
 /* See common/environ.h.  */
@@ -134,3 +167,17 @@ gdb_environ::envp () const
 {
   return const_cast<char **> (&m_environ_vector[0]);
 }
+
+/* See common/environ.h.  */
+
+const std::set<std::string> &
+gdb_environ::user_set_env () const
+{
+  return m_user_set_env;
+}
+
+const std::set<std::string> &
+gdb_environ::user_unset_env () const
+{
+  return m_user_unset_env;
+}
diff --git a/gdb/common/environ.h b/gdb/common/environ.h
index 0bbb191..4003f4e 100644
--- a/gdb/common/environ.h
+++ b/gdb/common/environ.h
@@ -18,6 +18,7 @@
 #define ENVIRON_H 1
 
 #include <vector>
+#include <set>
 
 /* Class that represents the environment variables as seen by the
    inferior.  */
@@ -41,12 +42,16 @@ public:
 
   /* Move constructor.  */
   gdb_environ (gdb_environ &&e)
-    : m_environ_vector (std::move (e.m_environ_vector))
+    : m_environ_vector (std::move (e.m_environ_vector)),
+      m_user_set_env (std::move (e.m_user_set_env)),
+      m_user_unset_env (std::move (e.m_user_unset_env))
   {
     /* Make sure that the moved-from vector is left at a valid
        state (only one NULL element).  */
     e.m_environ_vector.clear ();
     e.m_environ_vector.push_back (NULL);
+    e.m_user_set_env.clear ();
+    e.m_user_unset_env.clear ();
   }
 
   /* Move assignment.  */
@@ -73,9 +78,26 @@ public:
   /* Return the environment vector represented as a 'char **'.  */
   char **envp () const;
 
+  /* Return the user-set environment vector.  */
+  const std::set<std::string> &user_set_env () const;
+
+  /* Return the user-unset environment vector.  */
+  const std::set<std::string> &user_unset_env () const;
+
 private:
+  /* Unset VAR in environment.  If UPDATE_UNSET_LIST is true, then
+     also update M_USER_UNSET_ENV to reflect the unsetting of the
+     environment variable.  */
+  void unset (const char *var, bool update_unset_list);
+
   /* A vector containing the environment variables.  */
   std::vector<char *> m_environ_vector;
+
+  /* The environment variables explicitly set by the user.  */
+  std::set<std::string> m_user_set_env;
+
+  /* The environment variables explicitly unset by the user.  */
+  std::set<std::string> m_user_unset_env;
 };
 
 #endif /* defined (ENVIRON_H) */
diff --git a/gdb/common/rsp-low.c b/gdb/common/rsp-low.c
index eb85ab5..4befeb1 100644
--- a/gdb/common/rsp-low.c
+++ b/gdb/common/rsp-low.c
@@ -132,6 +132,30 @@ hex2bin (const char *hex, gdb_byte *bin, int count)
 
 /* See rsp-low.h.  */
 
+std::string
+hex2str (const char *hex)
+{
+  std::string ret;
+  size_t len = strlen (hex);
+
+  ret.reserve (len / 2);
+  for (size_t i = 0; i < len; ++i)
+    {
+      if (hex[0] == '\0' || hex[1] == '\0')
+	{
+	  /* Hex string is short, or of uneven length.  Return what we
+	     have so far.  */
+	  return ret;
+	}
+      ret += fromhex (hex[0]) * 16 + fromhex (hex[1]);
+      hex += 2;
+    }
+
+  return ret;
+}
+
+/* See rsp-low.h.  */
+
 int
 bin2hex (const gdb_byte *bin, char *hex, int count)
 {
@@ -146,6 +170,23 @@ bin2hex (const gdb_byte *bin, char *hex, int count)
   return i;
 }
 
+/* See rsp-low.h.  */
+
+std::string
+bin2hex (const gdb_byte *bin, int count)
+{
+  std::string ret;
+
+  ret.reserve (count * 2);
+  for (int i = 0; i < count; ++i)
+    {
+      ret += tohex ((*bin >> 4) & 0xf);
+      ret += tohex (*bin++ & 0xf);
+    }
+
+  return ret;
+}
+
 /* Return whether byte B needs escaping when sent as part of binary data.  */
 
 static int
diff --git a/gdb/common/rsp-low.h b/gdb/common/rsp-low.h
index b57f58b..2b3685f 100644
--- a/gdb/common/rsp-low.h
+++ b/gdb/common/rsp-low.h
@@ -52,6 +52,10 @@ extern char *unpack_varlen_hex (char *buff, ULONGEST *result);
 
 extern int hex2bin (const char *hex, gdb_byte *bin, int count);
 
+/* Like hex2bin, but return a std::string.  */
+
+extern std::string hex2str (const char *hex);
+
 /* Convert some bytes to a hexadecimal representation.  BIN holds the
    bytes to convert.  COUNT says how many bytes to convert.  The
    resulting characters are stored in HEX, followed by a NUL
@@ -59,6 +63,10 @@ extern int hex2bin (const char *hex, gdb_byte *bin, int count);
 
 extern int bin2hex (const gdb_byte *bin, char *hex, int count);
 
+/* Overloaded version of bin2hex that returns a std::string.  */
+
+extern std::string bin2hex (const gdb_byte *bin, int count);
+
 /* Convert BUFFER, binary data at least LEN_UNITS addressable memory units
    long, into escaped binary data in OUT_BUF.  Only copy memory units that fit
    completely in OUT_BUF.  Set *OUT_LEN_UNITS to the number of units from