Patchwork [v5] C++ify gdb/common/environ.c

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Submitter Sergio Durigan Junior
Date June 16, 2017, 10:23 p.m.
Message ID <20170616222315.12779-1-sergiodj@redhat.com>
Download mbox | patch
Permalink /patch/21058/
State New
Headers show

Comments

Sergio Durigan Junior - June 16, 2017, 10:23 p.m.
As part of the preparation necessary for my upcoming task, I'd like to
propose that we turn gdb_environ into a class.  The approach taken
here is simple: the class gdb_environ contains everything that is
needed to manipulate the environment variables.  These variables are
stored in an std::vector<char *>, which can be converted to a 'char
**' and passed as argument to functions that need it.

The usage has not changed much.  As per Pedro's suggestion, this class
uses a static factory method initialization.  This means that when an
instance is created, it is initially empty.  When needed, it has to be
initialized using the static method 'from_host_environ'.

As mentioned before, this is a preparation for an upcoming work that I
will be posting in the next few weeks or so.  For that work, I'll
probably create another data structure that will contain all the
environment variables that were set by the user using the 'set
environment' command, because I'll need access to them.  This will be
much easier with the class-ification of gdb_environ.

As noted, this has been regression-tested with the new version of
environ.exp and no regressions were found.

gdb/ChangeLog:
yyyy-mm-dd  Sergio Durigan Junior  <sergiodj@redhat.com>

	* Makefile.in (SUBDIR_UNITTESTS_SRCS): Add
	'unittests/environ-selftests.c'.
	(SUBDIR_UNITTESTS_OBS): Add 'environ-selftests.o'.
	* charset.c (find_charset_names): Declare object 'iconv_env'.
	Update code to use 'iconv_env' object.  Remove call to
	'free_environ'.
	* common/environ.c: Include <utility>.
	(make_environ): Delete function.
	(free_environ): Delete function.
	(gdb_environ::clear): New function.
	(gdb_environ::operator=): New function.
	(gdb_environ::get): Likewise.
	(environ_vector): Delete function.
	(set_in_environ): Delete function.
	(gdb_environ::set): New function.
	(unset_in_environ): Delete function.
	(gdb_environ::unset): New function.
	(gdb_environ::envp): Likewise.
	* common/environ.h: Include <vector>.
	(struct gdb_environ): Delete; transform into...
	(class gdb_environ): ... this class.
	(free_environ): Delete prototype.
	(init_environ, get_in_environ, set_in_environ, unset_in_environ,
	environ_vector): Likewise.
	* infcmd.c (run_command_1): Update code to call
	'envp' from 'gdb_environ' class.
	(environment_info): Update code to call methods from 'gdb_environ'
	class.
	(unset_environment_command): Likewise.
	(path_info): Likewise.
	(path_command): Likewise.
	* inferior.c (inferior::~inferior): Delete call to 'free_environ'.
	(inferior::inferior): Initialize 'environment' using the host's
	information.
	* inferior.h: Remove forward declaration of 'struct gdb_environ'.
	Include "environ.h".
	(class inferior) <environment>: Change type from 'struct
	gdb_environ' to 'gdb_environ'.
	* mi/mi-cmd-env.c (mi_cmd_env_path): Update code to call
	methods from 'gdb_environ' class.
	(mi_cmd_inferior_tty_show): Use 'getenv' instead of 'gdb_environ'.
	* solib.c (solib_find_1): Likewise
	* unittests/environ-selftests.c: New file.

gdb/gdbserver/ChangeLog:
yyyy-mm-dd  Sergio Durigan Junior  <sergiodj@redhat.com>

	* linux-low.c (linux_create_inferior): Adjust code to access the
	environment information via 'gdb_environ' class.
	* lynx-low.c (lynx_create_inferior): Likewise.
	* server.c (our_environ): Make it an instance of 'gdb_environ'.
	(get_environ): Return a pointer to 'our_environ'.
	(captured_main): Initialize 'our_environ'.
	* server.h (get_environ): Adjust prototype.
	* spu-low.c (spu_create_inferior): Adjust code to access the
	environment information via 'gdb_environ' class.
---
 gdb/Makefile.in                   |   2 +
 gdb/charset.c                     |  11 +--
 gdb/common/environ.c              | 201 +++++++++++++++-----------------------
 gdb/common/environ.h              |  59 +++++++----
 gdb/gdbserver/linux-low.c         |   2 +-
 gdb/gdbserver/lynx-low.c          |   2 +-
 gdb/gdbserver/server.c            |   9 +-
 gdb/gdbserver/server.h            |   6 +-
 gdb/gdbserver/spu-low.c           |   2 +-
 gdb/infcmd.c                      |  35 +++----
 gdb/inferior.c                    |   4 +-
 gdb/inferior.h                    |   6 +-
 gdb/mi/mi-cmd-env.c               |   6 +-
 gdb/solib.c                       |   7 +-
 gdb/unittests/environ-selftests.c |  87 +++++++++++++++++
 15 files changed, 247 insertions(+), 192 deletions(-)
 create mode 100644 gdb/unittests/environ-selftests.c
Simon Marchi - June 17, 2017, 8:54 a.m.
On 2017-06-17 00:23, Sergio Durigan Junior wrote:
>  void
> -set_in_environ (struct gdb_environ *e, const char *var, const char 
> *value)
> +gdb_environ::set (const char *var, const char *value)
>  {
> -  int i;
> -  int len = strlen (var);
> -  char **vector = e->vector;
> -  char *s;
> -
> -  for (i = 0; (s = vector[i]) != NULL; i++)
> -    if (strncmp (s, var, len) == 0 && s[len] == '=')
> -      break;
> +  /* We have to unset the variable in the vector if it exists.  */
> +  unset (var);
> 
> -  if (s == 0)
> -    {
> -      if (i == e->allocated)
> -	{
> -	  e->allocated += 10;
> -	  vector = (char **) xrealloc ((char *) vector,
> -				       (e->allocated + 1) * sizeof (char *));
> -	  e->vector = vector;
> -	}
> -      vector[i + 1] = 0;
> -    }
> -  else
> -    xfree (s);
> -
> -  s = (char *) xmalloc (len + strlen (value) + 2);
> -  strcpy (s, var);
> -  strcat (s, "=");
> -  strcat (s, value);
> -  vector[i] = s;
> -
> -  /* This used to handle setting the PATH and GNUTARGET variables
> -     specially.  The latter has been replaced by "set gnutarget"
> -     (which has worked since GDB 4.11).  The former affects searching
> -     the PATH to find SHELL, and searching the PATH to find the
> -     argument of "symbol-file" or "exec-file".  Maybe we should have
> -     some kind of "set exec-path" for that.  But in any event, having
> -     "set env" affect anything besides the inferior is a bad idea.
> -     What if we want to change the environment we pass to the program
> -     without afecting GDB's behavior?  */
> -
> -  return;
> +  /* Insert the element before the last one, which is always NULL.  */
> +  m_environ_vector.insert (m_environ_vector.end () - 1,
> +			   concat (var, "=", value, NULL));

The breaks if we have just constructed an empty gdb_environ object, as 
the vector is completely empty (no terminating NULL).  So we'd need some 
kind of check before that, if the vector is empty, add a NULL element...

I actually preferred the option of adding the NULL element to the vector 
in the gdb_environ constructor, since it allows always having the vector 
in a consistent state.  I don't think that avoiding that heap allocation 
is worth the complexity it adds to the code (unless we can prove 
otherwise by memory usage profiling).

> +static void
> +run_tests ()
> +{
> +  if (setenv ("GDB_SELFTEST_ENVIRON", "1", 1) != 0)
> +    error ("Could not set environment variable for testing.");
> +
> +  gdb_environ env;
> +
> +  SELF_CHECK (env.envp ()[0] == NULL);
> +
> +  SELF_CHECK (env.get ("PWD") == NULL);

If you add

   env.set ("PWD", "/home");

you should see a crash.

Simon
Sergio Durigan Junior - June 19, 2017, 4:19 a.m.
On Saturday, June 17 2017, Simon Marchi wrote:

> On 2017-06-17 00:23, Sergio Durigan Junior wrote:
>>  void
>> -set_in_environ (struct gdb_environ *e, const char *var, const char
>> *value)
>> +gdb_environ::set (const char *var, const char *value)
>>  {
>> -  int i;
>> -  int len = strlen (var);
>> -  char **vector = e->vector;
>> -  char *s;
>> -
>> -  for (i = 0; (s = vector[i]) != NULL; i++)
>> -    if (strncmp (s, var, len) == 0 && s[len] == '=')
>> -      break;
>> +  /* We have to unset the variable in the vector if it exists.  */
>> +  unset (var);
>>
>> -  if (s == 0)
>> -    {
>> -      if (i == e->allocated)
>> -	{
>> -	  e->allocated += 10;
>> -	  vector = (char **) xrealloc ((char *) vector,
>> -				       (e->allocated + 1) * sizeof (char *));
>> -	  e->vector = vector;
>> -	}
>> -      vector[i + 1] = 0;
>> -    }
>> -  else
>> -    xfree (s);
>> -
>> -  s = (char *) xmalloc (len + strlen (value) + 2);
>> -  strcpy (s, var);
>> -  strcat (s, "=");
>> -  strcat (s, value);
>> -  vector[i] = s;
>> -
>> -  /* This used to handle setting the PATH and GNUTARGET variables
>> -     specially.  The latter has been replaced by "set gnutarget"
>> -     (which has worked since GDB 4.11).  The former affects searching
>> -     the PATH to find SHELL, and searching the PATH to find the
>> -     argument of "symbol-file" or "exec-file".  Maybe we should have
>> -     some kind of "set exec-path" for that.  But in any event, having
>> -     "set env" affect anything besides the inferior is a bad idea.
>> -     What if we want to change the environment we pass to the program
>> -     without afecting GDB's behavior?  */
>> -
>> -  return;
>> +  /* Insert the element before the last one, which is always NULL.  */
>> +  m_environ_vector.insert (m_environ_vector.end () - 1,
>> +			   concat (var, "=", value, NULL));
>
> The breaks if we have just constructed an empty gdb_environ object, as
> the vector is completely empty (no terminating NULL).  So we'd need
> some kind of check before that, if the vector is empty, add a NULL
> element...
>
> I actually preferred the option of adding the NULL element to the
> vector in the gdb_environ constructor, since it allows always having
> the vector in a consistent state.  I don't think that avoiding that
> heap allocation is worth the complexity it adds to the code (unless we
> can prove otherwise by memory usage profiling).

I've had some time to think about this, and I agree.  I liked the code
better when it had the ctor doing the initialization of the vector.  I
think it also makes a lot more sense to always initialize the vector
with a NULL element, because this means we're correctly dealing with the
case where there's no environment variable to be passed to the inferior.

I'll update the code and re-submit the patch this way.

>
>> +static void
>> +run_tests ()
>> +{
>> +  if (setenv ("GDB_SELFTEST_ENVIRON", "1", 1) != 0)
>> +    error ("Could not set environment variable for testing.");
>> +
>> +  gdb_environ env;
>> +
>> +  SELF_CHECK (env.envp ()[0] == NULL);
>> +
>> +  SELF_CHECK (env.get ("PWD") == NULL);
>
> If you add
>
>   env.set ("PWD", "/home");
>
> you should see a crash.

Right.  I'll make sure to add this check as well.

Thanks,
Pedro Alves - June 19, 2017, 12:13 p.m.
On 06/17/2017 09:54 AM, Simon Marchi wrote:

> I actually preferred the option of adding the NULL element to the vector
> in the gdb_environ constructor, since it allows always having the vector
> in a consistent state.  I don't think that avoiding that heap allocation
> is worth the complexity it adds to the code (unless we can prove
> otherwise by memory usage profiling).

I'm not exactly sure what complexity this is, but I'm not going to
strongly object to always putting in the NULL element, since that's
what we currently do today.  This shows we're missing unit test coverage
at least.

I was going to write something longish about premature pessimization,
and on how that in my experience is really a mindset that ends up causing
us to leave a bunch of easy optimizations that all adding up, do matter
significantly, coming from actually running perf against gdb and seeing
the sometimes quite silly hot spots that could have been easily
avoided.  However, I found this article, and I find that it mirrors
perfectly my view, and is much better written than what I was going to say:

 http://www.bornsleepy.com/2014/10/27/premature-pessimization-and-the-like.html

I fully subscribe to the above.

Thanks,
Pedro Alves
Pedro Alves - June 19, 2017, 1:40 p.m.
On 06/19/2017 05:19 AM, Sergio Durigan Junior wrote:

> I
> think it also makes a lot more sense to always initialize the vector
> with a NULL element, because this means we're correctly dealing with the
> case where there's no environment variable to be passed to the inferior.

This sentence confuses me, because I don't understand what you mean
by "correctly" here.  What was incorrect?

Thanks,
Pedro Alves
Sergio Durigan Junior - June 19, 2017, 4:19 p.m.
On Monday, June 19 2017, Pedro Alves wrote:

> On 06/19/2017 05:19 AM, Sergio Durigan Junior wrote:
>
>> I
>> think it also makes a lot more sense to always initialize the vector
>> with a NULL element, because this means we're correctly dealing with the
>> case where there's no environment variable to be passed to the inferior.
>
> This sentence confuses me, because I don't understand what you mean
> by "correctly" here.  What was incorrect?

What I mean is that the internal state of the vector is correct from the
get-go.  As you said in another message, the environment vector passed
to the exec* family of syscalls should contain at least one element,
NULL.  This means we can make sure that the vector generated by the API
(via the envp method) obeys this rule, or that the internal vector
(m_environ_vector) obeys this rule.  I prefer the second method, because
it leaves everything (internal and external) in a correct state.

I don't have any advanced C++ arguments to base my opinion on, and I am
well aware that this means preallocating things that maybe didn't need
to be allocated, but I still prefer keeping the NULL element there
because it makes more sense to me.

My half-cent to this discussion.

Thanks,

Patch

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 5e5fcaa..40b17f9 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -526,6 +526,7 @@  SUBDIR_PYTHON_LDFLAGS =
 SUBDIR_PYTHON_CFLAGS =
 
 SUBDIR_UNITTESTS_SRCS = \
+	unittests/environ-selftests.c \
 	unittests/function-view-selftests.c \
 	unittests/offset-type-selftests.c \
 	unittests/optional-selftests.c \
@@ -533,6 +534,7 @@  SUBDIR_UNITTESTS_SRCS = \
 	unittests/scoped_restore-selftests.c
 
 SUBDIR_UNITTESTS_OBS = \
+	environ-selftests.o \
 	function-view-selftests.o \
 	offset-type-selftests.o \
 	optional-selftests.o \
diff --git a/gdb/charset.c b/gdb/charset.c
index dbe46a4..be95bbe 100644
--- a/gdb/charset.c
+++ b/gdb/charset.c
@@ -794,16 +794,14 @@  find_charset_names (void)
   int err, status;
   int fail = 1;
   int flags;
-  struct gdb_environ *iconv_env;
+  gdb_environ iconv_env = gdb_environ::from_host_environ ();
   char *iconv_program;
 
   /* Older iconvs, e.g. 2.2.2, don't omit the intro text if stdout is
      not a tty.  We need to recognize it and ignore it.  This text is
      subject to translation, so force LANGUAGE=C.  */
-  iconv_env = make_environ ();
-  init_environ (iconv_env);
-  set_in_environ (iconv_env, "LANGUAGE", "C");
-  set_in_environ (iconv_env, "LC_ALL", "C");
+  iconv_env.set ("LANGUAGE", "C");
+  iconv_env.set ("LC_ALL", "C");
 
   child = pex_init (PEX_USE_PIPES, "iconv", NULL);
 
@@ -827,7 +825,7 @@  find_charset_names (void)
   /* Note that we simply ignore errors here.  */
   if (!pex_run_in_environment (child, flags,
 			       args[0], const_cast<char **> (args),
-			       environ_vector (iconv_env),
+			       iconv_env.envp (),
 			       NULL, NULL, &err))
     {
       FILE *in = pex_read_output (child, 0);
@@ -901,7 +899,6 @@  find_charset_names (void)
 
   xfree (iconv_program);
   pex_free (child);
-  free_environ (iconv_env);
 
   if (fail)
     {
diff --git a/gdb/common/environ.c b/gdb/common/environ.c
index 3145d01..c67124b 100644
--- a/gdb/common/environ.c
+++ b/gdb/common/environ.c
@@ -18,165 +18,118 @@ 
 #include "common-defs.h"
 #include "environ.h"
 #include <algorithm>
-
+#include <utility>
 
-/* Return a new environment object.  */
+/* See common/environ.h.  */
 
-struct gdb_environ *
-make_environ (void)
+gdb_environ &
+gdb_environ::operator= (gdb_environ &&e)
 {
-  struct gdb_environ *e;
-
-  e = XNEW (struct gdb_environ);
-
-  e->allocated = 10;
-  e->vector = (char **) xmalloc ((e->allocated + 1) * sizeof (char *));
-  e->vector[0] = 0;
-  return e;
-}
-
-/* Free an environment and all the strings in it.  */
-
-void
-free_environ (struct gdb_environ *e)
-{
-  char **vector = e->vector;
-
-  while (*vector)
-    xfree (*vector++);
-
-  xfree (e->vector);
-  xfree (e);
+  clear ();
+  m_environ_vector = std::move (e.m_environ_vector);
+  return *this;
 }
 
-/* Copy the environment given to this process into E.
-   Also copies all the strings in it, so we can be sure
-   that all strings in these environments are safe to free.  */
-
-void
-init_environ (struct gdb_environ *e)
+/* Create a gdb_environ object using the host's environment
+   variables.  */
+gdb_environ gdb_environ::from_host_environ ()
 {
   extern char **environ;
-  int i;
+  gdb_environ e;
 
   if (environ == NULL)
-    return;
+    return e;
 
-  for (i = 0; environ[i]; i++) /*EMPTY */ ;
+  for (int i = 0; environ[i] != NULL; ++i)
+    e.m_environ_vector.push_back (xstrdup (environ[i]));
 
-  if (e->allocated < i)
-    {
-      e->allocated = std::max (i, e->allocated + 10);
-      e->vector = (char **) xrealloc ((char *) e->vector,
-				      (e->allocated + 1) * sizeof (char *));
-    }
+  /* The last element of the vector is always going to be NULL.  */
+  e.m_environ_vector.push_back (NULL);
 
-  memcpy (e->vector, environ, (i + 1) * sizeof (char *));
+  return e;
+}
 
-  while (--i >= 0)
-    {
-      int len = strlen (e->vector[i]);
-      char *newobj = (char *) xmalloc (len + 1);
+/* See common/environ.h.  */
 
-      memcpy (newobj, e->vector[i], len + 1);
-      e->vector[i] = newobj;
-    }
+void
+gdb_environ::clear ()
+{
+  for (char *v : m_environ_vector)
+    xfree (v);
+  m_environ_vector.clear ();
 }
 
-/* Return the vector of environment E.
-   This is used to get something to pass to execve.  */
+/* Helper function to check if STRING contains an environment variable
+   assignment of VAR, i.e., if STRING starts with 'VAR='.  Return true
+   if it contains, false otherwise.  */
 
-char **
-environ_vector (struct gdb_environ *e)
+static bool
+match_var_in_string (char *string, const char *var, size_t var_len)
 {
-  return e->vector;
+  if (strncmp (string, var, var_len) == 0 && string[var_len] == '=')
+    return true;
+
+  return false;
 }
-
-/* Return the value in environment E of variable VAR.  */
 
-char *
-get_in_environ (const struct gdb_environ *e, const char *var)
+/* See common/environ.h.  */
+
+const char *
+gdb_environ::get (const char *var) const
 {
-  int len = strlen (var);
-  char **vector = e->vector;
-  char *s;
+  size_t len = strlen (var);
 
-  for (; (s = *vector) != NULL; vector++)
-    if (strncmp (s, var, len) == 0 && s[len] == '=')
-      return &s[len + 1];
+  for (char *el : m_environ_vector)
+    if (el != NULL && match_var_in_string (el, var, len))
+      return &el[len + 1];
 
-  return 0;
+  return NULL;
 }
 
-/* Store the value in E of VAR as VALUE.  */
+/* See common/environ.h.  */
 
 void
-set_in_environ (struct gdb_environ *e, const char *var, const char *value)
+gdb_environ::set (const char *var, const char *value)
 {
-  int i;
-  int len = strlen (var);
-  char **vector = e->vector;
-  char *s;
-
-  for (i = 0; (s = vector[i]) != NULL; i++)
-    if (strncmp (s, var, len) == 0 && s[len] == '=')
-      break;
+  /* We have to unset the variable in the vector if it exists.  */
+  unset (var);
 
-  if (s == 0)
-    {
-      if (i == e->allocated)
-	{
-	  e->allocated += 10;
-	  vector = (char **) xrealloc ((char *) vector,
-				       (e->allocated + 1) * sizeof (char *));
-	  e->vector = vector;
-	}
-      vector[i + 1] = 0;
-    }
-  else
-    xfree (s);
-
-  s = (char *) xmalloc (len + strlen (value) + 2);
-  strcpy (s, var);
-  strcat (s, "=");
-  strcat (s, value);
-  vector[i] = s;
-
-  /* This used to handle setting the PATH and GNUTARGET variables
-     specially.  The latter has been replaced by "set gnutarget"
-     (which has worked since GDB 4.11).  The former affects searching
-     the PATH to find SHELL, and searching the PATH to find the
-     argument of "symbol-file" or "exec-file".  Maybe we should have
-     some kind of "set exec-path" for that.  But in any event, having
-     "set env" affect anything besides the inferior is a bad idea.
-     What if we want to change the environment we pass to the program
-     without afecting GDB's behavior?  */
-
-  return;
+  /* Insert the element before the last one, which is always NULL.  */
+  m_environ_vector.insert (m_environ_vector.end () - 1,
+			   concat (var, "=", value, NULL));
 }
 
-/* Remove the setting for variable VAR from environment E.  */
+/* See common/environ.h.  */
 
 void
-unset_in_environ (struct gdb_environ *e, const char *var)
+gdb_environ::unset (const char *var)
 {
-  int len = strlen (var);
-  char **vector = e->vector;
-  char *s;
+  size_t len = strlen (var);
+
+  /* We iterate until '.cend () - 1' because the last element is
+     always NULL.  */
+  for (std::vector<char *>::const_iterator el = m_environ_vector.cbegin ();
+       el != m_environ_vector.cend () - 1;
+       ++el)
+    if (match_var_in_string (*el, var, len))
+      {
+	xfree (*el);
+	m_environ_vector.erase (el);
+	break;
+      }
+}
+
+/* See common/environ.h.  */
 
-  for (; (s = *vector) != NULL; vector++)
+char **
+gdb_environ::envp () const
+{
+  if (m_environ_vector.empty ())
     {
-      if (strncmp (s, var, len) == 0 && s[len] == '=')
-	{
-	  xfree (s);
-	  /* Walk through the vector, shuffling args down by one, including
-	     the NULL terminator.  Can't use memcpy() here since the regions
-	     overlap, and memmove() might not be available.  */
-	  while ((vector[0] = vector[1]) != NULL)
-	    {
-	      vector++;
-	    }
-	  break;
-	}
+      static const char *const empty_envp[1] = { NULL };
+
+      return const_cast<char **> (empty_envp);
     }
+
+  return const_cast<char **> (&m_environ_vector[0]);
 }
diff --git a/gdb/common/environ.h b/gdb/common/environ.h
index 3ace69e..7b529b5 100644
--- a/gdb/common/environ.h
+++ b/gdb/common/environ.h
@@ -17,33 +17,54 @@ 
 #if !defined (ENVIRON_H)
 #define ENVIRON_H 1
 
-/* We manipulate environments represented as these structures.  */
+#include <vector>
 
-struct gdb_environ
+/* Class that represents the environment variables as seen by the
+   inferior.  */
+
+class gdb_environ
+{
+public:
+  /* Regular constructor and destructor.  */
+  gdb_environ () {}
+
+  ~gdb_environ ()
   {
-    /* Number of usable slots allocated in VECTOR.
-       VECTOR always has one slot not counted here,
-       to hold the terminating zero.  */
-    int allocated;
-    /* A vector of slots, ALLOCATED + 1 of them.
-       The first few slots contain strings "VAR=VALUE"
-       and the next one contains zero.
-       Then come some unused slots.  */
-    char **vector;
-  };
+    clear ();
+  }
+
+  /* Move constructor.  */
+  gdb_environ (gdb_environ &&e)
+    : m_environ_vector (std::move (e.m_environ_vector))
+  {}
+
+  /* Move assignment.  */
+  gdb_environ &operator= (gdb_environ &&e);
 
-extern struct gdb_environ *make_environ (void);
+  static gdb_environ from_host_environ ();
 
-extern void free_environ (struct gdb_environ *);
+  /* Clear the environment variables stored in the object.  */
+  void clear ();
 
-extern void init_environ (struct gdb_environ *);
+  /* Return the value in the environment for the variable VAR.  The
+     return pointer is only valid as long as VAR is not
+     removed/replaced from the environment.  */
+  const char *get (const char *var) const;
 
-extern char *get_in_environ (const struct gdb_environ *, const char *);
+  /* Store VAR=VALUE in the environment.  */
+  void set (const char *var, const char *value);
 
-extern void set_in_environ (struct gdb_environ *, const char *, const char *);
+  /* Unset VAR in environment.  */
+  void unset (const char *var);
 
-extern void unset_in_environ (struct gdb_environ *, const char *);
+  /* Return the environment vector represented as a 'char **'.  */
+  char **envp () const;
 
-extern char **environ_vector (struct gdb_environ *);
+private:
+  /* A vector containing the environment variables.  This is useful
+     for when we need to obtain a 'char **' with all the existing
+     variables.  */
+  std::vector<char *> m_environ_vector;
+};
 
 #endif /* defined (ENVIRON_H) */
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 7fbf744..5be38f1 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -998,7 +998,7 @@  linux_create_inferior (const char *program,
 
   pid = fork_inferior (program,
 		       str_program_args.c_str (),
-		       environ_vector (get_environ ()), linux_ptrace_fun,
+		       get_environ ()->envp (), linux_ptrace_fun,
 		       NULL, NULL, NULL, NULL);
 
   do_cleanups (restore_personality);
diff --git a/gdb/gdbserver/lynx-low.c b/gdb/gdbserver/lynx-low.c
index 35160d6..77f570e 100644
--- a/gdb/gdbserver/lynx-low.c
+++ b/gdb/gdbserver/lynx-low.c
@@ -259,7 +259,7 @@  lynx_create_inferior (const char *program,
 
   pid = fork_inferior (program,
 		       str_program_args.c_str (),
-		       environ_vector (get_environ ()), lynx_ptrace_fun,
+		       get_environ ()->envp (), lynx_ptrace_fun,
 		       NULL, NULL, NULL, NULL);
 
   post_fork_inferior (pid, program);
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index 1d7a8b0..3838351 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -42,7 +42,7 @@ 
 
 /* The environment to pass to the inferior when creating it.  */
 
-struct gdb_environ *our_environ = NULL;
+static gdb_environ our_environ;
 
 /* Start the inferior using a shell.  */
 
@@ -257,10 +257,10 @@  get_exec_file (int err)
 
 /* See server.h.  */
 
-struct gdb_environ *
+gdb_environ *
 get_environ ()
 {
-  return our_environ;
+  return &our_environ;
 }
 
 static int
@@ -3698,8 +3698,7 @@  captured_main (int argc, char *argv[])
     }
 
   /* Gather information about the environment.  */
-  our_environ = make_environ ();
-  init_environ (our_environ);
+  our_environ = gdb_environ::from_host_environ ();
 
   initialize_async_io ();
   initialize_low ();
diff --git a/gdb/gdbserver/server.h b/gdb/gdbserver/server.h
index 4de4244..46b614c 100644
--- a/gdb/gdbserver/server.h
+++ b/gdb/gdbserver/server.h
@@ -62,6 +62,7 @@  int vsnprintf(char *str, size_t size, const char *format, va_list ap);
 #include "mem-break.h"
 #include "gdbthread.h"
 #include "inferiors.h"
+#include "environ.h"
 
 /* Target-specific functions */
 
@@ -154,9 +155,8 @@  extern int in_queued_stop_replies (ptid_t ptid);
    inferior and PROGRAM is its name.  */
 extern void post_fork_inferior (int pid, const char *program);
 
-/* Get the 'struct gdb_environ *' being used in the current
-   session.  */
-extern struct gdb_environ *get_environ ();
+/* Get the gdb_environ being used in the current session.  */
+extern gdb_environ *get_environ ();
 
 extern target_waitstatus last_status;
 extern ptid_t last_ptid;
diff --git a/gdb/gdbserver/spu-low.c b/gdb/gdbserver/spu-low.c
index 0f770a0..6362502 100644
--- a/gdb/gdbserver/spu-low.c
+++ b/gdb/gdbserver/spu-low.c
@@ -289,7 +289,7 @@  spu_create_inferior (const char *program,
 
   pid = fork_inferior (program,
 		       str_program_args.c_str (),
-		       environ_vector (get_environ ()), spu_ptrace_fun,
+		       get_environ ()->envp (), spu_ptrace_fun,
 		       NULL, NULL, NULL, NULL);
 
   post_fork_inferior (pid, program);
diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index d551639..ee0754d 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -610,7 +610,7 @@  run_command_1 (char *args, int from_tty, int tbreak_at_main)
      the value now.  */
   run_target->to_create_inferior (run_target, exec_file,
 				  std::string (get_inferior_args ()),
-				  environ_vector (current_inferior ()->environment),
+				  current_inferior ()->environment.envp (),
 				  from_tty);
   /* to_create_inferior should push the target, so after this point we
      shouldn't refer to run_target again.  */
@@ -2131,7 +2131,7 @@  environment_info (char *var, int from_tty)
 {
   if (var)
     {
-      char *val = get_in_environ (current_inferior ()->environment, var);
+      const char *val = current_inferior ()->environment.get (var);
 
       if (val)
 	{
@@ -2149,13 +2149,14 @@  environment_info (char *var, int from_tty)
     }
   else
     {
-      char **vector = environ_vector (current_inferior ()->environment);
+      char **envp = current_inferior ()->environment.envp ();
 
-      while (*vector)
-	{
-	  puts_filtered (*vector++);
-	  puts_filtered ("\n");
-	}
+      if (envp != NULL)
+	for (int idx = 0; envp[idx] != NULL; ++idx)
+	  {
+	    puts_filtered (envp[idx]);
+	    puts_filtered ("\n");
+	  }
     }
 }
 
@@ -2215,10 +2216,10 @@  set_environment_command (char *arg, int from_tty)
       printf_filtered (_("Setting environment variable "
 			 "\"%s\" to null value.\n"),
 		       var);
-      set_in_environ (current_inferior ()->environment, var, "");
+      current_inferior ()->environment.set (var, "");
     }
   else
-    set_in_environ (current_inferior ()->environment, var, val);
+    current_inferior ()->environment.set (var, val);
   xfree (var);
 }
 
@@ -2230,13 +2231,10 @@  unset_environment_command (char *var, int from_tty)
       /* If there is no argument, delete all environment variables.
          Ask for confirmation if reading from the terminal.  */
       if (!from_tty || query (_("Delete all environment variables? ")))
-	{
-	  free_environ (current_inferior ()->environment);
-	  current_inferior ()->environment = make_environ ();
-	}
+	current_inferior ()->environment = gdb_environ::from_host_environ ();
     }
   else
-    unset_in_environ (current_inferior ()->environment, var);
+    current_inferior ()->environment.unset (var);
 }
 
 /* Handle the execution path (PATH variable).  */
@@ -2247,8 +2245,7 @@  static void
 path_info (char *args, int from_tty)
 {
   puts_filtered ("Executable and object file path: ");
-  puts_filtered (get_in_environ (current_inferior ()->environment,
-				 path_var_name));
+  puts_filtered (current_inferior ()->environment.get (path_var_name));
   puts_filtered ("\n");
 }
 
@@ -2261,13 +2258,13 @@  path_command (char *dirname, int from_tty)
   const char *env;
 
   dont_repeat ();
-  env = get_in_environ (current_inferior ()->environment, path_var_name);
+  env = current_inferior ()->environment.get (path_var_name);
   /* Can be null if path is not set.  */
   if (!env)
     env = "";
   exec_path = xstrdup (env);
   mod_path (dirname, &exec_path);
-  set_in_environ (current_inferior ()->environment, path_var_name, exec_path);
+  current_inferior ()->environment.set (path_var_name, exec_path);
   xfree (exec_path);
   if (from_tty)
     path_info ((char *) NULL, from_tty);
diff --git a/gdb/inferior.c b/gdb/inferior.c
index 0b655f4..9fa2dad 100644
--- a/gdb/inferior.c
+++ b/gdb/inferior.c
@@ -81,7 +81,6 @@  inferior::~inferior ()
   inferior_free_data (inf);
   xfree (inf->args);
   xfree (inf->terminal);
-  free_environ (inf->environment);
   target_desc_info_free (inf->tdesc_info);
   xfree (inf->priv);
 }
@@ -89,10 +88,9 @@  inferior::~inferior ()
 inferior::inferior (int pid_)
   : num (++highest_inferior_num),
     pid (pid_),
-    environment (make_environ ()),
+    environment (gdb_environ::from_host_environ ()),
     registry_data ()
 {
-  init_environ (this->environment);
   inferior_alloc_data (this);
 }
 
diff --git a/gdb/inferior.h b/gdb/inferior.h
index 1c541b7..8ada4f8 100644
--- a/gdb/inferior.h
+++ b/gdb/inferior.h
@@ -30,7 +30,6 @@  struct regcache;
 struct ui_out;
 struct terminal_info;
 struct target_desc_info;
-struct gdb_environ;
 struct continuation;
 struct inferior;
 
@@ -43,6 +42,9 @@  struct inferior;
 /* For struct frame_id.  */
 #include "frame.h"
 
+/* For gdb_environ.  */
+#include "environ.h"
+
 #include "progspace.h"
 #include "registry.h"
 
@@ -363,7 +365,7 @@  public:
 
   /* Environment to use for running inferior,
      in format described in environ.h.  */
-  gdb_environ *environment = NULL;
+  gdb_environ environment;
 
   /* True if this child process was attached rather than forked.  */
   bool attach_flag = false;
diff --git a/gdb/mi/mi-cmd-env.c b/gdb/mi/mi-cmd-env.c
index 4093178..a06d08a 100644
--- a/gdb/mi/mi-cmd-env.c
+++ b/gdb/mi/mi-cmd-env.c
@@ -167,7 +167,7 @@  mi_cmd_env_path (const char *command, char **argv, int argc)
   else
     {
       /* Otherwise, get current path to modify.  */
-      env = get_in_environ (current_inferior ()->environment, path_var_name);
+      env = current_inferior ()->environment.get (path_var_name);
 
       /* Can be null if path is not set.  */
       if (!env)
@@ -178,9 +178,9 @@  mi_cmd_env_path (const char *command, char **argv, int argc)
   for (i = argc - 1; i >= 0; --i)
     env_mod_path (argv[i], &exec_path);
 
-  set_in_environ (current_inferior ()->environment, path_var_name, exec_path);
+  current_inferior ()->environment.set (path_var_name, exec_path);
   xfree (exec_path);
-  env = get_in_environ (current_inferior ()->environment, path_var_name);
+  env = current_inferior ()->environment.get (path_var_name);
   uiout->field_string ("path", env);
 }
 
diff --git a/gdb/solib.c b/gdb/solib.c
index 491c18a..788cf15 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -350,16 +350,15 @@  solib_find_1 (const char *in_pathname, int *fd, int is_solib)
 
   /* If not found, next search the inferior's $PATH environment variable.  */
   if (found_file < 0 && sysroot == NULL)
-    found_file = openp (get_in_environ (current_inferior ()->environment,
-					"PATH"),
+    found_file = openp (current_inferior ()->environment.get ("PATH"),
 			OPF_TRY_CWD_FIRST | OPF_RETURN_REALPATH, in_pathname,
 			O_RDONLY | O_BINARY, &temp_pathname);
 
   /* If not found, and we're looking for a solib, next search the
      inferior's $LD_LIBRARY_PATH environment variable.  */
   if (is_solib && found_file < 0 && sysroot == NULL)
-    found_file = openp (get_in_environ (current_inferior ()->environment,
-					"LD_LIBRARY_PATH"),
+    found_file = openp (current_inferior ()->environment.get
+			("LD_LIBRARY_PATH"),
 			OPF_TRY_CWD_FIRST | OPF_RETURN_REALPATH, in_pathname,
 			O_RDONLY | O_BINARY, &temp_pathname);
 
diff --git a/gdb/unittests/environ-selftests.c b/gdb/unittests/environ-selftests.c
new file mode 100644
index 0000000..3757cc5
--- /dev/null
+++ b/gdb/unittests/environ-selftests.c
@@ -0,0 +1,87 @@ 
+/* Self tests for gdb_environ for GDB, the GNU debugger.
+
+   Copyright (C) 2017 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 "defs.h"
+#include "selftest.h"
+#include "common/environ.h"
+
+namespace selftests {
+namespace gdb_environ_tests {
+
+static void
+run_tests ()
+{
+  if (setenv ("GDB_SELFTEST_ENVIRON", "1", 1) != 0)
+    error ("Could not set environment variable for testing.");
+
+  gdb_environ env;
+
+  SELF_CHECK (env.envp ()[0] == NULL);
+
+  SELF_CHECK (env.get ("PWD") == NULL);
+
+  env = gdb_environ::from_host_environ ();
+
+  SELF_CHECK (strcmp (env.get ("GDB_SELFTEST_ENVIRON"), "1") == 0);
+
+  env.set ("GDB_SELFTEST_ENVIRON", "test");
+  SELF_CHECK (strcmp (env.get ("GDB_SELFTEST_ENVIRON"), "test") == 0);
+
+  env.unset ("GDB_SELFTEST_ENVIRON");
+  SELF_CHECK (env.get ("GDB_SELFTEST_ENVIRON") == NULL);
+
+  env.set ("GDB_SELFTEST_ENVIRON", "1");
+  SELF_CHECK (strcmp (env.get ("GDB_SELFTEST_ENVIRON"), "1") == 0);
+
+  env.clear ();
+
+  SELF_CHECK (env.envp ()[0] == NULL);
+
+  SELF_CHECK (env.get ("GDB_SELFTEST_ENVIRON") == NULL);
+
+  env = gdb_environ::from_host_environ ();
+  char **envp = env.envp ();
+  int num_found = 0;
+
+  for (size_t i = 0; envp[i] != NULL; ++i)
+    if (strcmp (envp[i], "GDB_SELFTEST_ENVIRON=1") == 0)
+      ++num_found;
+
+  SELF_CHECK (num_found == 1);
+
+  unsetenv ("GDB_SELFTEST_ENVIRON");
+
+  env.set ("GDB_SELFTEST_ENVIRON_1", "aaa");
+  SELF_CHECK (strcmp (env.get ("GDB_SELFTEST_ENVIRON_1"), "aaa") == 0);
+
+  env.set ("GDB_SELFTEST_ENVIRON_2", "bbb");
+  SELF_CHECK (strcmp (env.get ("GDB_SELFTEST_ENVIRON_2"), "bbb") == 0);
+
+  env.unset ("GDB_SELFTEST_ENVIRON_1");
+  SELF_CHECK (env.get ("GDB_SELFTEST_ENVIRON_1") == NULL);
+  SELF_CHECK (strcmp (env.get ("GDB_SELFTEST_ENVIRON_2"), "bbb") == 0);
+}
+} /* namespace gdb_environ */
+} /* namespace selftests */
+
+void
+_initialize_environ_selftests ()
+{
+  register_self_test (selftests::gdb_environ_tests::run_tests);
+}