Replace the libc environment with a thread-safe emulation

putenv(3) and friends aren't thread-safe regardless of how you slice
it; a global lock around all environment operations (like before)
keeps things safe as far as our own operations go, but we have
absolutely no control over what libc or a library dragged in by a
driver/NIF does -- they're free to call getenv(3) or putenv(3)
without honoring our lock.

This commit solves this by setting up an "emulated" environment which
can't be touched without going through our interfaces. Third-party
libraries can still shoot themselves in the foot but benign uses of
os:putenv/2 will no longer risk crashing the emulator.

8 files changed, 989 insertions, 591 deletions

diff --git a/erts/emulator/sys/common/erl_osenv.c b/erts/emulator/sys/common/erl_osenv.c
new file mode 100644
index 0000000000..9f54d1dff0
--- /dev/null
+++ b/erts/emulator/sys/common/erl_osenv.c
@@ -0,0 +1,396 @@
+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 2017. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * %CopyrightEnd%
+ */
+
+#include "erl_osenv.h"
+
+#include "global.h"
+#include "erl_alloc.h"
+#include "erl_process.h"
+
+#define STACKBUF_SIZE (512)
+
+typedef struct __env_rbtnode_t {
+    struct __env_rbtnode_t *parent;
+    struct __env_rbtnode_t *left;
+    struct __env_rbtnode_t *right;
+
+    int is_red;
+
+    erts_osenv_data_t key;
+    erts_osenv_data_t value;
+} env_rbtnode_t;
+
+#define ERTS_RBT_PREFIX env
+#define ERTS_RBT_T env_rbtnode_t
+#define ERTS_RBT_KEY_T erts_osenv_data_t
+#define ERTS_RBT_FLAGS_T int
+#define ERTS_RBT_INIT_EMPTY_TNODE(T) \
+    do { \
+        (T)->parent = NULL; \
+        (T)->left = NULL; \
+        (T)->right = NULL; \
+        (T)->is_red = 0; \
+    } while(0)
+#define ERTS_RBT_IS_RED(T) ((T)->is_red)
+#define ERTS_RBT_SET_RED(T) ((T)->is_red = 1)
+#define ERTS_RBT_IS_BLACK(T) (!ERTS_RBT_IS_RED(T))
+#define ERTS_RBT_SET_BLACK(T) ((T)->is_red = 0)
+#define ERTS_RBT_GET_FLAGS(T) ((T)->is_red)
+#define ERTS_RBT_SET_FLAGS(T, F) ((T)->is_red = F)
+#define ERTS_RBT_GET_PARENT(T) ((T)->parent)
+#define ERTS_RBT_SET_PARENT(T, P) ((T)->parent = P)
+#define ERTS_RBT_GET_RIGHT(T) ((T)->right)
+#define ERTS_RBT_SET_RIGHT(T, R) ((T)->right = (R))
+#define ERTS_RBT_GET_LEFT(T) ((T)->left)
+#define ERTS_RBT_SET_LEFT(T, L) ((T)->left = (L))
+#define ERTS_RBT_GET_KEY(T) ((T)->key)
+#define ERTS_RBT_IS_LT(KX, KY) (compare_env_keys(KX, KY) < 0)
+#define ERTS_RBT_IS_EQ(KX, KY) (compare_env_keys(KX, KY) == 0)
+#define ERTS_RBT_WANT_FOREACH_DESTROY
+#define ERTS_RBT_WANT_FOREACH
+#define ERTS_RBT_WANT_REPLACE
+#define ERTS_RBT_WANT_DELETE
+#define ERTS_RBT_WANT_INSERT
+#define ERTS_RBT_WANT_LOOKUP
+
+static int compare_env_keys(const erts_osenv_data_t a, const erts_osenv_data_t b);
+
+#include "erl_rbtree.h"
+
+static int compare_env_keys(const erts_osenv_data_t a, const erts_osenv_data_t b) {
+    int relation = sys_memcmp(a.data, b.data, MIN(a.length, b.length));
+
+    if(relation != 0) {
+        return relation;
+    }
+
+    if(a.length < b.length) {
+        return -1;
+    } else if(a.length == b.length) {
+        return 0;
+    } else {
+        return 1;
+    }
+}
+
+static void *convert_value_to_native(Eterm term, char *stackbuf,
+        int stackbuf_size, Sint *length) {
+    int encoding;
+    void *result;
+
+    if(is_atom(term)) {
+        return NULL;
+    }
+
+    encoding = erts_get_native_filename_encoding();
+    *length = erts_native_filename_need(term, encoding);
+
+    if(*length < 0) {
+        return NULL;
+    } else if(*length >= stackbuf_size) {
+        result = erts_alloc(ERTS_ALC_T_TMP, *length);
+    } else {
+        result = stackbuf;
+    }
+
+    erts_native_filename_put(term, encoding, (byte*)result);
+
+    return result;
+}
+
+static void *convert_key_to_native(Eterm term, char *stackbuf,
+        int stackbuf_size, Sint *length) {
+    byte *name_iterator, *name_end;
+    void *result;
+    int encoding;
+
+    result = convert_value_to_native(term, stackbuf, stackbuf_size, length);
+
+    if(result == NULL || length == 0) {
+        return NULL;
+    }
+
+    encoding = erts_get_native_filename_encoding();
+
+    name_iterator = (byte*)result;
+    name_end = &name_iterator[*length];
+
+#ifdef __WIN32__
+    /* Windows stores per-drive working directories as variables starting with
+     * '=', so we skip the first character to tolerate that. */
+    name_iterator = erts_raw_env_next_char(name_iterator, encoding);
+#endif
+
+    while(name_iterator < name_end) {
+        if(erts_raw_env_char_is_7bit_ascii_char('=', name_iterator, encoding)) {
+            if(result != stackbuf) {
+                erts_free(ERTS_ALC_T_TMP, result);
+            }
+
+            return NULL;
+        }
+
+        name_iterator = erts_raw_env_next_char(name_iterator, encoding);
+    }
+
+    return result;
+}
+
+void erts_osenv_init(erts_osenv_t *env) {
+    env->variable_count = 0;
+    env->content_size = 0;
+    env->tree = NULL;
+}
+
+static void destroy_foreach(env_rbtnode_t *node, void *_state) {
+    erts_free(ERTS_ALC_T_ENVIRONMENT, node);
+    (void)_state;
+}
+
+void erts_osenv_clear(erts_osenv_t *env) {
+    env_rbt_foreach_destroy(&env->tree, &destroy_foreach, NULL);
+    erts_osenv_init(env);
+}
+
+struct __env_merge {
+    int overwrite_existing;
+    erts_osenv_t *env;
+};
+
+static void merge_foreach(env_rbtnode_t *node, void *_state) {
+    struct __env_merge *state = (struct __env_merge*)(_state);
+    env_rbtnode_t *existing_node;
+
+    existing_node = env_rbt_lookup(state->env->tree, node->key);
+
+    if(existing_node == NULL || state->overwrite_existing) {
+        erts_osenv_put_native(state->env, &node->key, &node->value);
+    }
+}
+
+void erts_osenv_merge(erts_osenv_t *env, const erts_osenv_t *with, int overwrite) {
+    struct __env_merge merge_state;
+
+    merge_state.overwrite_existing = overwrite;
+    merge_state.env = env;
+
+    env_rbt_foreach(with->tree, merge_foreach, &merge_state);
+}
+
+struct __env_foreach_term {
+    erts_osenv_foreach_term_cb_t user_callback;
+    struct process *process;
+    void *user_state;
+};
+
+static void foreach_term_wrapper(env_rbtnode_t *node, void *_state) {
+    struct __env_foreach_term *state = (struct __env_foreach_term*)_state;
+    Eterm key, value;
+
+    key = erts_convert_native_to_filename(state->process,
+        node->key.length, (byte*)node->key.data);
+    value = erts_convert_native_to_filename(state->process,
+        node->value.length, (byte*)node->value.data);
+
+    state->user_callback(state->process, state->user_state, key, value);
+}
+
+void erts_osenv_foreach_term(const erts_osenv_t *env, struct process *process,
+        void *state, erts_osenv_foreach_term_cb_t callback) {
+    struct __env_foreach_term wrapper_state;
+
+    wrapper_state.user_callback = callback;
+    wrapper_state.user_state = state;
+    wrapper_state.process = process;
+
+    env_rbt_foreach(env->tree, foreach_term_wrapper, &wrapper_state);
+}
+
+int erts_osenv_get_term(const erts_osenv_t *env, Process *process,
+        Eterm key_term, Eterm *out_term) {
+    char key_stackbuf[STACKBUF_SIZE];
+    erts_osenv_data_t key;
+    int result;
+
+    key.data = convert_key_to_native(key_term, key_stackbuf,
+        STACKBUF_SIZE, &key.length);
+    result = -1;
+
+    if(key.data != NULL) {
+        env_rbtnode_t *node;
+
+        node = env_rbt_lookup(env->tree, key);
+        result = 0;
+
+        if(node != NULL) {
+            (*out_term) = erts_convert_native_to_filename(process,
+                node->value.length, (byte*)node->value.data);
+            result = 1;
+        }
+
+        if(key.data != key_stackbuf) {
+            erts_free(ERTS_ALC_T_TMP, key.data);
+        }
+    }
+
+    return result;
+}
+
+int erts_osenv_put_term(erts_osenv_t *env, Eterm key_term, Eterm value_term) {
+    char key_stackbuf[STACKBUF_SIZE], value_stackbuf[STACKBUF_SIZE];
+    erts_osenv_data_t key, value;
+    int result;
+
+    key.data = convert_key_to_native(key_term, key_stackbuf,
+        STACKBUF_SIZE, &key.length);
+    value.data = convert_value_to_native(value_term, value_stackbuf,
+        STACKBUF_SIZE, &value.length);
+    result = -1;
+
+    if(value.data != NULL && key.data != NULL) {
+        result = erts_osenv_put_native(env, &key, &value);
+    }
+
+    if(value.data != NULL && value.data != value_stackbuf) {
+        erts_free(ERTS_ALC_T_TMP, value.data);
+    }
+
+    if(key.data != NULL && key.data != key_stackbuf) {
+        erts_free(ERTS_ALC_T_TMP, key.data);
+    }
+
+    return result;
+}
+
+int erts_osenv_unset_term(erts_osenv_t *env, Eterm key_term) {
+    char key_stackbuf[STACKBUF_SIZE];
+    erts_osenv_data_t key;
+    int result;
+
+    key.data = convert_key_to_native(key_term, key_stackbuf,
+        STACKBUF_SIZE, &key.length);
+    result = -1;
+
+    if(key.data != NULL) {
+        result = erts_osenv_unset_native(env, &key);
+
+        if(key.data != key_stackbuf) {
+            erts_free(ERTS_ALC_T_TMP, key.data);
+        }
+    }
+
+    return result;
+}
+
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+struct __env_foreach_native {
+    erts_osenv_foreach_native_cb_t user_callback;
+    void *user_state;
+};
+
+static void foreach_native_wrapper(env_rbtnode_t *node, void *_state) {
+    struct __env_foreach_native *state = (struct __env_foreach_native*)_state;
+
+    state->user_callback(state->user_state, &node->key, &node->value);
+}
+
+void erts_osenv_foreach_native(const erts_osenv_t *env, void *state,
+        erts_osenv_foreach_native_cb_t callback) {
+    struct __env_foreach_native wrapper_state;
+
+    wrapper_state.user_callback = callback;
+    wrapper_state.user_state = state;
+
+    env_rbt_foreach(env->tree, foreach_native_wrapper, &wrapper_state);
+}
+
+int erts_osenv_get_native(const erts_osenv_t *env,
+        const erts_osenv_data_t *key,
+        erts_osenv_data_t *value) {
+    env_rbtnode_t *node = env_rbt_lookup(env->tree, *key);
+
+    if(node != NULL) {
+        if(value != NULL) {
+            if(node->value.length > value->length) {
+                return -1;
+            }
+
+            sys_memcpy(value->data, node->value.data, node->value.length);
+            value->length = node->value.length;
+        }
+
+        return 1;
+    }
+
+    return 0;
+}
+
+int erts_osenv_put_native(erts_osenv_t *env, const erts_osenv_data_t *key,
+        const erts_osenv_data_t *value) {
+    env_rbtnode_t *old_node, *new_node;
+
+    new_node = erts_alloc(ERTS_ALC_T_ENVIRONMENT, sizeof(env_rbtnode_t) +
+        key->length + value->length);
+
+    new_node->key.data = (char*)(&new_node[1]);
+    new_node->key.length = key->length;
+    new_node->value.data = &((char*)new_node->key.data)[key->length];
+    new_node->value.length = value->length;
+
+    sys_memcpy(new_node->key.data, key->data, key->length);
+    sys_memcpy(new_node->value.data, value->data, value->length);
+
+    old_node = env_rbt_lookup(env->tree, *key);
+
+    if(old_node != NULL) {
+        env->content_size -= old_node->value.length;
+        env->content_size -= old_node->key.length;
+        env_rbt_replace(&env->tree, old_node, new_node);
+    } else {
+        env_rbt_insert(&env->tree, new_node);
+        env->variable_count++;
+    }
+
+    env->content_size += new_node->value.length;
+    env->content_size += new_node->key.length;
+
+    if(old_node != NULL) {
+        erts_free(ERTS_ALC_T_ENVIRONMENT, old_node);
+    }
+
+    return 1;
+}
+
+int erts_osenv_unset_native(erts_osenv_t *env, const erts_osenv_data_t *key) {
+    env_rbtnode_t *old_node = env_rbt_lookup(env->tree, *key);
+
+    if(old_node != NULL) {
+        env->content_size -= old_node->value.length;
+        env->content_size -= old_node->key.length;
+        env->variable_count -= 1;
+
+        env_rbt_delete(&env->tree, old_node);
+        erts_free(ERTS_ALC_T_ENVIRONMENT, old_node);
+        return 1;
+    }
+
+    return 0;
+}
diff --git a/erts/emulator/sys/common/erl_osenv.h b/erts/emulator/sys/common/erl_osenv.h
new file mode 100644
index 0000000000..4777f2148a
--- /dev/null
+++ b/erts/emulator/sys/common/erl_osenv.h
@@ -0,0 +1,121 @@
+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 2017. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * %CopyrightEnd%
+ */
+
+/* This is a replacement for getenv(3) and friends, operating on instances so
+ * we can keep a common implementation for both the global and local (per-port)
+ * environments.
+ *
+ * The instances are not thread-safe on their own but unlike getenv(3) we're
+ * guaranteed to be the only user, so placing locks around all our accesses
+ * will suffice.
+ *
+ * Use erts_sys_rwlock_global_osenv to access the global environment. */
+
+#ifndef __ERL_OSENV_H__
+#define __ERL_OSENV_H__
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+typedef struct __erts_osenv_data_t erts_osenv_data_t;
+
+typedef struct __erts_osenv_t {
+    struct __env_rbtnode_t *tree;
+    int variable_count;
+    int content_size;
+} erts_osenv_t;
+
+#include "sys.h"
+
+struct __erts_osenv_data_t {
+    Sint length;
+    void *data;
+};
+
+void erts_osenv_init(erts_osenv_t *env);
+void erts_osenv_clear(erts_osenv_t *env);
+
+/* @brief Merges \c with into \c env
+ *
+ * @param overwrite Whether to overwrite existing entries or keep them as they
+ * are. */
+void erts_osenv_merge(erts_osenv_t *env, const erts_osenv_t *with, int overwrite);
+
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/* @brief Copies env[key] into \c value
+ *
+ * @return 1 on success, 0 if the key couldn't be found, and -1 if the input
+ * was invalid. */
+int erts_osenv_get_term(const erts_osenv_t *env, struct process *process,
+    Eterm key, Eterm *value);
+
+/* @brief Copies \c value into \c env[key]
+ *
+ * @return 1 on success, -1 if the input was invalid. */
+int erts_osenv_put_term(erts_osenv_t *env, Eterm key, Eterm value);
+
+/* @brief Removes \c env[key]
+ *
+ * @return 1 on success, 0 if the key couldn't be found, and -1 if the input
+ * was invalid. */
+int erts_osenv_unset_term(erts_osenv_t *env, Eterm key);
+
+/* @brief Copies env[key] into \c value
+ *
+ * @param value [in,out] The buffer to copy the value into, may be NULL if you
+ * only wish to query presence.
+ *
+ * @return 1 on success, 0 if the key couldn't be found, and -1 if if the value
+ * didn't fit into the buffer. */
+int erts_osenv_get_native(const erts_osenv_t *env, const erts_osenv_data_t *key,
+    erts_osenv_data_t *value);
+
+/* @brief Copies \c value into \c env[key]
+ *
+ * @return 1 on success, -1 on failure. */
+int erts_osenv_put_native(erts_osenv_t *env, const erts_osenv_data_t *key,
+    const erts_osenv_data_t *value);
+
+/* @brief Removes \c key from the env.
+ *
+ * @return 1 on success, 0 if the key couldn't be found. */
+int erts_osenv_unset_native(erts_osenv_t *env, const erts_osenv_data_t *key);
+
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+typedef void (*erts_osenv_foreach_term_cb_t)(struct process *process,
+    void *state, Eterm key, Eterm value);
+
+typedef void (*erts_osenv_foreach_native_cb_t)(void *state,
+    const erts_osenv_data_t *key,
+    const erts_osenv_data_t *value);
+
+/* @brief Walks through all environment variables, calling \c callback for each
+ * one. It's unsafe to modify \c env within the callback. */
+void erts_osenv_foreach_term(const erts_osenv_t *env, struct process *process,
+    void *state, erts_osenv_foreach_term_cb_t callback);
+
+/* @copydoc erts_osenv_foreach_term */
+void erts_osenv_foreach_native(const erts_osenv_t *env, void *state,
+    erts_osenv_foreach_native_cb_t callback);
+
+#endif
diff --git a/erts/emulator/sys/unix/erl_unix_sys.h b/erts/emulator/sys/unix/erl_unix_sys.h
index b6f5b319ee..e367d565a7 100644
--- a/erts/emulator/sys/unix/erl_unix_sys.h
+++ b/erts/emulator/sys/unix/erl_unix_sys.h
@@ -133,7 +133,7 @@
 #define  ERTS_SYS_CONTINOUS_FD_NUMBERS
 
 
-typedef void *GETENV_STATE;
+void erts_sys_env_init(void);
 
 /*
 ** For the erl_timer_sup module.
diff --git a/erts/emulator/sys/unix/sys.c b/erts/emulator/sys/unix/sys.c
index 6315135151..189ca083d7 100644
--- a/erts/emulator/sys/unix/sys.c
+++ b/erts/emulator/sys/unix/sys.c
@@ -62,9 +62,6 @@
 
 #include "erl_mseg.h"
 
-extern char **environ;
-erts_rwmtx_t environ_rwmtx;
-
 #define MAX_VSIZE 16		/* Max number of entries allowed in an I/O
 				 * vector sock_sendv().
 				 */
@@ -77,7 +74,7 @@ erts_rwmtx_t environ_rwmtx;
 
 #include "erl_check_io.h"
 #include "erl_cpu_topology.h"
-
+#include "erl_osenv.h"
 extern int  driver_interrupt(int, int);
 extern void do_break(void);
 
@@ -454,10 +451,10 @@ prepare_crash_dump(int secs)
     close(crashdump_companion_cube_fd);
 
     envsz = sizeof(env);
-    i = erts_sys_getenv__("ERL_CRASH_DUMP_NICE", env, &envsz);
+    i = erts_sys_explicit_8bit_getenv("ERL_CRASH_DUMP_NICE", env, &envsz);
     if (i >= 0) {
 	int nice_val;
-	nice_val = i != 0 ? 0 : atoi(env);
+	nice_val = i != 1 ? 0 : atoi(env);
 	if (nice_val > 39) {
 	    nice_val = 39;
 	}
@@ -749,34 +746,6 @@ void os_version(int *pMajor, int *pMinor, int *pBuild) {
     *pBuild = get_number(&release); /* Pointer to build number. */
 }
 
-void init_getenv_state(GETENV_STATE *state)
-{
-   erts_rwmtx_rlock(&environ_rwmtx);
-   *state = NULL;
-}
-
-char *getenv_string(GETENV_STATE *state0)
-{
-   char **state = (char **) *state0;
-   char *cp;
-
-   ERTS_LC_ASSERT(erts_lc_rwmtx_is_rlocked(&environ_rwmtx));
-
-   if (state == NULL)
-      state = environ;
-
-   cp = *state++;
-   *state0 = (GETENV_STATE) state;
-
-   return cp;
-}
-
-void fini_getenv_state(GETENV_STATE *state)
-{
-   *state = NULL;
-   erts_rwmtx_runlock(&environ_rwmtx);
-}
-
 void erts_do_break_handling(void)
 {
     struct termios temp_mode;
@@ -830,90 +799,6 @@ void sys_get_pid(char *buffer, size_t buffer_size){
     erts_snprintf(buffer, buffer_size, "%lu",(unsigned long) p);
 }
 
-int
-erts_sys_putenv_raw(char *key, char *value) {
-    return erts_sys_putenv(key, value);
-}
-int
-erts_sys_putenv(char *key, char *value)
-{
-    int res;
-    char *env;
-    Uint need = strlen(key) + strlen(value) + 2;
-
-#ifdef HAVE_COPYING_PUTENV
-    env = erts_alloc(ERTS_ALC_T_TMP, need);
-#else
-    env = erts_alloc(ERTS_ALC_T_PUTENV_STR, need);
-    erts_atomic_add_nob(&sys_misc_mem_sz, need);
-#endif
-    strcpy(env,key);
-    strcat(env,"=");
-    strcat(env,value);
-    erts_rwmtx_rwlock(&environ_rwmtx);
-    res = putenv(env);
-    erts_rwmtx_rwunlock(&environ_rwmtx);
-#ifdef HAVE_COPYING_PUTENV
-    erts_free(ERTS_ALC_T_TMP, env);
-#endif
-    return res;
-}
-
-int
-erts_sys_getenv__(char *key, char *value, size_t *size)
-{
-    int res;
-    char *orig_value = getenv(key);
-    if (!orig_value)
-	res = -1;
-    else {
-	size_t len = sys_strlen(orig_value);
-	if (len >= *size) {
-	    *size = len + 1;
-	    res = 1;
-	}
-	else {
-	    *size = len;
-	    sys_memcpy((void *) value, (void *) orig_value, len+1);
-	    res = 0;
-	}
-    }
-    return res;
-}
-
-int
-erts_sys_getenv_raw(char *key, char *value, size_t *size) {
-    return erts_sys_getenv(key, value, size);
-}
-
-/*
- * erts_sys_getenv
- * returns:
- *  -1, if environment key is not set with a value
- *   0, if environment key is set and value fits into buffer size
- *   1, if environment key is set but does not fit into buffer size
- *      size is set with the needed buffer size value
- */
-
-int
-erts_sys_getenv(char *key, char *value, size_t *size)
-{
-    int res;
-    erts_rwmtx_rlock(&environ_rwmtx);
-    res = erts_sys_getenv__(key, value, size);
-    erts_rwmtx_runlock(&environ_rwmtx);
-    return res;
-}
-
-int
-erts_sys_unsetenv(char *key)
-{
-    int res;
-    erts_rwmtx_rwlock(&environ_rwmtx);
-    res = unsetenv(key);
-    erts_rwmtx_rwunlock(&environ_rwmtx);
-    return res;
-}
 
 void sys_init_io(void) { }
 void erts_sys_alloc_init(void) { }
@@ -1260,14 +1145,9 @@ erts_sys_main_thread(void)
     }
 }
 
-
 void
 erl_sys_args(int* argc, char** argv)
 {
-
-    erts_rwmtx_init(&environ_rwmtx, "environ", NIL,
-        ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_GENERIC);
-
     ASSERT(argc && argv);
 
     max_files = erts_check_io_max_files();
@@ -1275,4 +1155,5 @@ erl_sys_args(int* argc, char** argv)
     init_smp_sig_notify();
     init_smp_sig_suspend();
 
+    erts_sys_env_init();
 }
diff --git a/erts/emulator/sys/unix/sys_drivers.c b/erts/emulator/sys/unix/sys_drivers.c
index 0228e1af54..b7ac89d89a 100644
--- a/erts/emulator/sys/unix/sys_drivers.c
+++ b/erts/emulator/sys/unix/sys_drivers.c
@@ -55,9 +55,6 @@
 
 #include "erl_threads.h"
 
-extern char **environ;
-extern erts_rwmtx_t environ_rwmtx;
-
 extern erts_atomic_t sys_misc_mem_sz;
 
 static Eterm forker_port;
@@ -180,7 +177,7 @@ erl_sys_late_init(void)
     opts.read_write = 0;
     opts.hide_window = 0;
     opts.wd = NULL;
-    opts.envir = NULL;
+    erts_osenv_init(&opts.envir);
     opts.exit_status = 0;
     opts.overlapped_io = 0;
     opts.spawn_type = ERTS_SPAWN_ANY;
@@ -443,85 +440,55 @@ static void close_pipes(int ifd[2], int ofd[2])
     close(ofd[1]);
 }
 
-static char **build_unix_environment(char *block)
+struct __add_spawn_env_state {
+    struct iovec *iov;
+    int *iov_index;
+
+    Sint32 *payload_size;
+    char *env_block;
+};
+
+static void add_spawn_env_block_foreach(void *_state,
+                                        const erts_osenv_data_t *key,
+                                        const erts_osenv_data_t *value)
 {
-    int i;
-    int j;
-    int len;
-    char *cp;
-    char **cpp;
-    char** old_env;
-    
-    ERTS_LC_ASSERT(erts_lc_rwmtx_is_rlocked(&environ_rwmtx));
-
-    cp = block;
-    len = 0;
-    while (*cp != '\0') {
-	cp += strlen(cp) + 1;
-	len++;
-    }
-    old_env = environ;
-    while (*old_env++ != NULL) {
-	len++;
-    }
-    
-    cpp = (char **) erts_alloc_fnf(ERTS_ALC_T_ENVIRONMENT,
-				   sizeof(char *) * (len+1));
-    if (cpp == NULL) {
-	return NULL;
-    }
+    struct __add_spawn_env_state *state;
+    struct iovec *iov;
 
-    cp = block;
-    len = 0;
-    while (*cp != '\0') {
-	cpp[len] = cp;
-	cp += strlen(cp) + 1;
-	len++;
-    }
-    
-    i = len;
-    for (old_env = environ; *old_env; old_env++) {
-	char* old = *old_env;
-
-	for (j = 0; j < len; j++) {
-	    char *s, *t;
-
-	    /* check if cpp[j] equals old
-	       before the = sign,
-	       i.e.
-	       "TMPDIR=/tmp/" */
-	    s = cpp[j];
-	    t = old;
-	    while (*s == *t && *s != '=') {
-		s++, t++;
-	    }
-	    if (*s == '=' && *t == '=') {
-		break;
-	    }
-	}
+    state = (struct __add_spawn_env_state*)(_state);
+    iov = &state->iov[*state->iov_index];
 
-	if (j == len) {		/* New version not found */
-	    cpp[len++] = old;
-	}
-    }
+    iov->iov_base = state->env_block;
 
-    for (j = 0; j < i; ) {
-        size_t last = strlen(cpp[j])-1;
-	if (cpp[j][last] == '=' && strchr(cpp[j], '=') == cpp[j]+last) {
-	    cpp[j] = cpp[--len];
-	    if (len < i) {
-		i--;
-	    } else {
-		j++;
-	    }
-	}
-	else {
-	    j++;
-	}
-    }
+    sys_memcpy(state->env_block, key->data, key->length);
+    state->env_block += key->length;
+    *state->env_block++ = '=';
+    sys_memcpy(state->env_block, value->data, value->length);
+    state->env_block += value->length;
+    *state->env_block++ = '\0';
 
-    cpp[len] = NULL;
-    return cpp;
+    iov->iov_len = state->env_block - (char*)iov->iov_base;
+
+    (*state->payload_size) += iov->iov_len;
+    (*state->iov_index)++;
+}
+
+static void *add_spawn_env_block(const erts_osenv_t *env, struct iovec *iov,
+                                  int *iov_index, Sint32 *payload_size) {
+    struct __add_spawn_env_state add_state;
+    char *env_block;
+
+    env_block = erts_alloc(ERTS_ALC_T_TMP, env->content_size +
+        env->variable_count * sizeof("=\0"));
+
+    add_state.iov = iov;
+    add_state.iov_index = iov_index;
+    add_state.env_block = env_block;
+    add_state.payload_size = payload_size;
+
+    erts_osenv_foreach_native(env, &add_state, add_spawn_env_block_foreach);
+
+    return env_block;
 }
 
 static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
@@ -531,7 +498,6 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
 #define CMD_LINE_PREFIX_STR_SZ (sizeof(CMD_LINE_PREFIX_STR) - 1)
 
     int len;
-    char **new_environ;
     ErtsSysDriverData *dd;
     char *cmd_line;
     char wd_buff[MAXPATHLEN+1];
@@ -598,19 +564,7 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
 	memcpy((void *) (cmd_line + CMD_LINE_PREFIX_STR_SZ), (void *) name, len);
 	cmd_line[CMD_LINE_PREFIX_STR_SZ + len] = '\0';
 	len = CMD_LINE_PREFIX_STR_SZ + len + 1;
-    }
-
-    erts_rwmtx_rlock(&environ_rwmtx);
-
-    if (opts->envir == NULL) {
-	new_environ = environ;
-    } else if ((new_environ = build_unix_environment(opts->envir)) == NULL) {
-	erts_rwmtx_runlock(&environ_rwmtx);
-        close_pipes(ifd, ofd);
-	erts_free(ERTS_ALC_T_TMP, (void *) cmd_line);
-	errno = ENOMEM;
-	return ERL_DRV_ERROR_ERRNO;
-    }
+}
 
     if ((cwd = getcwd(wd_buff, MAXPATHLEN+1)) == NULL) {
         /* on some OSs this call opens a fd in the
@@ -619,9 +573,6 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
         int err = errno;
         close_pipes(ifd, ofd);
         erts_free(ERTS_ALC_T_TMP, (void *) cmd_line);
-        if (new_environ != environ)
-            erts_free(ERTS_ALC_T_ENVIRONMENT, (void *) new_environ);
-        erts_rwmtx_runlock(&environ_rwmtx);
         errno = err;
         return ERL_DRV_ERROR_ERRNO;
     }
@@ -629,6 +580,7 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
     wd = opts->wd;
 
     {
+        void *environment_block;
         struct iovec *io_vector;
         int iov_len = 5;
         char nullbuff[] = "\0";
@@ -641,10 +593,8 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
 
         if (wd) iov_len++;
 
-        /* count number of elements in environment */
-        while(new_environ[env_len] != NULL)
-            env_len++;
-        iov_len += 1 + env_len; /* num envs including size int */
+        /* num envs including size int */
+        iov_len += 1 + opts->envir.variable_count;
 
         /* count number of element in argument list */
         if (opts->spawn_type == ERTS_SPAWN_EXECUTABLE) {
@@ -661,10 +611,7 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
 
         if (!io_vector) {
             close_pipes(ifd, ofd);
-            erts_rwmtx_runlock(&environ_rwmtx);
             erts_free(ERTS_ALC_T_TMP, (void *) cmd_line);
-            if (new_environ != environ)
-                erts_free(ERTS_ALC_T_ENVIRONMENT, (void *) new_environ);
             errno = ENOMEM;
             return ERL_DRV_ERROR_ERRNO;
         }
@@ -699,16 +646,13 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
         io_vector[i++].iov_len = 1;
         buffsz += io_vector[i-1].iov_len;
 
+        env_len = htonl(opts->envir.variable_count);
         io_vector[i].iov_base = (void*)&env_len;
-        env_len = htonl(env_len);
         io_vector[i++].iov_len = sizeof(env_len);
         buffsz += io_vector[i-1].iov_len;
 
-        for (j = 0; new_environ[j] != NULL; j++) {
-            io_vector[i].iov_base = new_environ[j];
-            io_vector[i++].iov_len = strlen(new_environ[j]) + 1;
-            buffsz += io_vector[i-1].iov_len;
-        }
+        environment_block = add_spawn_env_block(&opts->envir, io_vector, &i,
+            &buffsz);
 
         /* only append arguments if this was a spawn_executable */
         if (opts->spawn_type == ERTS_SPAWN_EXECUTABLE) {
@@ -744,9 +688,6 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
                 int err = errno;
                 close_pipes(ifd, ofd);
                 erts_free(ERTS_ALC_T_TMP, io_vector);
-                if (new_environ != environ)
-                    erts_free(ERTS_ALC_T_ENVIRONMENT, (void *) new_environ);
-                erts_rwmtx_runlock(&environ_rwmtx);
                 erts_free(ERTS_ALC_T_TMP, (void *) cmd_line);
                 errno = err;
                 return ERL_DRV_ERROR_ERRNO;
@@ -767,16 +708,12 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name,
             driver_select(port_num, ofd[1], ERL_DRV_WRITE|ERL_DRV_USE, 1);
         }
 
+        erts_free(ERTS_ALC_T_TMP, environment_block);
         erts_free(ERTS_ALC_T_TMP, io_vector);
     }
 
     erts_free(ERTS_ALC_T_TMP, (void *) cmd_line);
 
-    if (new_environ != environ)
-	erts_free(ERTS_ALC_T_ENVIRONMENT, (void *) new_environ);
-
-    erts_rwmtx_runlock(&environ_rwmtx);
-
     dd = create_driver_data(port_num, ifd[0], ofd[1], opts->packet_bytes,
                              DO_WRITE | DO_READ, opts->exit_status,
                              0, 0);
@@ -1652,15 +1589,13 @@ static ErlDrvData forker_start(ErlDrvPort port_num, char* name,
 
     forker_port = erts_drvport2id(port_num);
 
-    res = erts_sys_getenv_raw("BINDIR", bindir, &bindirsz);
-    if (res != 0) {
-        if (res < 0)
-            erts_exit(1,
-                     "Environment variable BINDIR is not set\n");
-        if (res > 0)
-            erts_exit(1,
-                     "Value of environment variable BINDIR is too large\n");
+    res = erts_sys_explicit_8bit_getenv("BINDIR", bindir, &bindirsz);
+    if (res == 0) {
+        erts_exit(1, "Environment variable BINDIR is not set\n");
+    } else if(res < 0) {
+        erts_exit(1, "Value of environment variable BINDIR is too large\n");
     }
+
     if (bindir[0] != DIR_SEPARATOR_CHAR)
         erts_exit(1,
                  "Environment variable BINDIR does not contain an"
diff --git a/erts/emulator/sys/unix/sys_env.c b/erts/emulator/sys/unix/sys_env.c
new file mode 100644
index 0000000000..4d8301f985
--- /dev/null
+++ b/erts/emulator/sys/unix/sys_env.c
@@ -0,0 +1,133 @@
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include "sys.h"
+#include "erl_osenv.h"
+#include "erl_alloc.h"
+
+#include "erl_thr_progress.h"
+
+static erts_osenv_t sysenv_global_env;
+static erts_rwmtx_t sysenv_rwmtx;
+
+extern char **environ;
+
+static void import_initial_env(void);
+
+void erts_sys_env_init() {
+    erts_rwmtx_init(&sysenv_rwmtx, "environ", NIL,
+        ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_GENERIC);
+
+    erts_osenv_init(&sysenv_global_env);
+    import_initial_env();
+}
+
+const erts_osenv_t *erts_sys_rlock_global_osenv() {
+    erts_rwmtx_rlock(&sysenv_rwmtx);
+    return &sysenv_global_env;
+}
+
+erts_osenv_t *erts_sys_rwlock_global_osenv() {
+    erts_rwmtx_rwlock(&sysenv_rwmtx);
+    return &sysenv_global_env;
+}
+
+void erts_sys_rwunlock_global_osenv() {
+    erts_rwmtx_rwunlock(&sysenv_rwmtx);
+}
+
+void erts_sys_runlock_global_osenv() {
+    erts_rwmtx_runlock(&sysenv_rwmtx);
+}
+
+int erts_sys_explicit_8bit_putenv(char *key, char *value) {
+    erts_osenv_data_t env_key, env_value;
+    int result;
+
+    env_key.length = sys_strlen(key);
+    env_key.data = key;
+
+    env_value.length = sys_strlen(value);
+    env_value.data = value;
+
+    {
+        erts_osenv_t *env = erts_sys_rwlock_global_osenv();
+        result = erts_osenv_put_native(env, &env_key, &env_value);
+        erts_sys_rwunlock_global_osenv();
+    }
+
+    return result;
+}
+
+int erts_sys_explicit_8bit_getenv(char *key, char *value, size_t *size) {
+    erts_osenv_data_t env_key, env_value;
+    int result;
+
+    env_key.length = sys_strlen(key);
+    env_key.data = key;
+
+    /* Reserve space for NUL termination. */
+    env_value.length = *size - 1;
+    env_value.data = value;
+
+    {
+        const erts_osenv_t *env = erts_sys_rlock_global_osenv();
+        result = erts_osenv_get_native(env, &env_key, &env_value);
+        erts_sys_runlock_global_osenv();
+    }
+
+    if(result == 1) {
+        value[env_value.length] = '\0';
+    }
+
+    *size = env_value.length;
+
+    return result;
+}
+
+int erts_sys_explicit_host_getenv(char *key, char *value, size_t *size) {
+    char *orig_value;
+    size_t length;
+    
+    orig_value = getenv(key);
+
+    if(orig_value == NULL) {
+        return 0;
+    }
+
+    length = sys_strlen(orig_value);
+
+    if (length >= *size) {
+        *size = length + 1;
+        return -1;
+    }
+
+    sys_memcpy((void*)value, (void*)orig_value, length + 1);
+    *size = length;
+
+    return 1;
+}
+
+static void import_initial_env(void) {
+    char **environ_iterator, *environ_variable;
+
+    environ_iterator = environ;
+
+    while ((environ_variable = *(environ_iterator++)) != NULL) {
+        char *separator_index = strchr(environ_variable, '=');
+
+        if (separator_index != NULL) {
+            erts_osenv_data_t env_key, env_value;
+
+            env_key.length = separator_index - environ_variable;
+            env_key.data = environ_variable;
+    
+            env_value.length = sys_strlen(separator_index) - 1;
+            env_value.data = separator_index + 1;
+
+            erts_osenv_put_native(&sysenv_global_env, &env_key, &env_value);
+        }
+    }
+}
diff --git a/erts/emulator/sys/win32/sys.c b/erts/emulator/sys/win32/sys.c
index 0598a12351..a1c630d68a 100644
--- a/erts/emulator/sys/win32/sys.c
+++ b/erts/emulator/sys/win32/sys.c
@@ -77,6 +77,7 @@ static int create_pipe(LPHANDLE, LPHANDLE, BOOL, BOOL);
 static int application_type(const wchar_t* originalName, wchar_t fullPath[MAX_PATH],
 			   BOOL search_in_path, BOOL handle_quotes,
 			   int *error_return);
+static void *build_env_block(const erts_osenv_t *env);
 
 HANDLE erts_service_event;
 
@@ -1190,7 +1191,6 @@ spawn_start(ErlDrvPort port_num, char* utf8_name, SysDriverOpts* opts)
     int ok;
     int neededSelects = 0;
     SECURITY_ATTRIBUTES sa = {sizeof(SECURITY_ATTRIBUTES), NULL, TRUE};
-    char* envir = opts->envir;
     int errno_return = -1;
     wchar_t *name;
     int len;
@@ -1265,29 +1265,33 @@ spawn_start(ErlDrvPort port_num, char* utf8_name, SysDriverOpts* opts)
 	name[i] = L'\0';
     }
     DEBUGF(("Spawning \"%S\"\n", name));
-    envir = win_build_environment(envir); /* Always a unicode environment */ 
-    ok = create_child_process(name,
-			      hChildStdin,
-			      hChildStdout,
-			      hChildStderr,
-			      &dp->port_pid,
-			      &pid,
-			      opts->hide_window,
-			      (LPVOID) envir,
-			      (wchar_t *) opts->wd,
-			      opts->spawn_type,
-			      (wchar_t **) opts->argv,
-			      &errno_return);
-    CloseHandle(hChildStdin);
-    CloseHandle(hChildStdout);
-    if (close_child_stderr && hChildStderr != INVALID_HANDLE_VALUE &&
-	hChildStderr != 0) {
-	CloseHandle(hChildStderr);
-    }
-    erts_free(ERTS_ALC_T_TMP, name);
-
-    if (envir != NULL) {
-	erts_free(ERTS_ALC_T_ENVIRONMENT, envir);
+
+    {
+        void *environment_block = build_env_block(&opts->envir);
+
+        ok = create_child_process(name,
+                                  hChildStdin,
+                                  hChildStdout,
+                                  hChildStderr,
+                                  &dp->port_pid,
+                                  &pid,
+                                  opts->hide_window,
+                                  environment_block,
+                                  (wchar_t *) opts->wd,
+                                  opts->spawn_type,
+                                  (wchar_t **) opts->argv,
+                                  &errno_return);
+
+        CloseHandle(hChildStdin);
+        CloseHandle(hChildStdout);
+
+        if (close_child_stderr && hChildStderr != INVALID_HANDLE_VALUE &&
+            hChildStderr != 0) {
+            CloseHandle(hChildStderr);
+        }
+
+        erts_free(ERTS_ALC_T_TMP, environment_block);
+        erts_free(ERTS_ALC_T_TMP, name);
     }
 
     if (!ok) {
@@ -1338,6 +1342,41 @@ spawn_start(ErlDrvPort port_num, char* utf8_name, SysDriverOpts* opts)
     return retval;
 }
 
+struct __build_env_state {
+    WCHAR *next_variable;
+};
+
+static void build_env_foreach(void *_state, const erts_osenv_data_t *key,
+                              const erts_osenv_data_t *value)
+{
+    struct __build_env_state *state = (struct __build_env_state*)(_state);
+
+    sys_memcpy(state->next_variable, key->data, key->length);
+    state->next_variable += (int)key->length / sizeof(WCHAR);
+    *state->next_variable++ = L'=';
+
+    sys_memcpy(state->next_variable, value->data, value->length);
+    state->next_variable += (int)value->length / sizeof(WCHAR);
+    *state->next_variable++ = L'\0';
+}
+
+/* Builds an environment block suitable for CreateProcessW. */
+static void *build_env_block(const erts_osenv_t *env) {
+    struct __build_env_state build_state;
+    WCHAR *env_block;
+
+    env_block = erts_alloc(ERTS_ALC_T_TMP, env->content_size +
+        (env->variable_count * sizeof(L"=\0") + sizeof(L'\0')));
+
+    build_state.next_variable = env_block;
+
+    erts_osenv_foreach_native(env, &build_state, build_env_foreach);
+
+    (*build_state.next_variable) = L'\0';
+
+    return env_block;
+}
+
 static int
 create_file_thread(AsyncIo* aio, int mode)
 {
diff --git a/erts/emulator/sys/win32/sys_env.c b/erts/emulator/sys/win32/sys_env.c
index 5792816267..c78161b344 100644
--- a/erts/emulator/sys/win32/sys_env.c
+++ b/erts/emulator/sys/win32/sys_env.c
@@ -1,319 +1,212 @@
-/*

- * %CopyrightBegin%

- *

- * Copyright Ericsson AB 2002-2016. All Rights Reserved.

- *

- * Licensed under the Apache License, Version 2.0 (the "License");

- * you may not use this file except in compliance with the License.

- * You may obtain a copy of the License at

- *

- *     http://www.apache.org/licenses/LICENSE-2.0

- *

- * Unless required by applicable law or agreed to in writing, software

- * distributed under the License is distributed on an "AS IS" BASIS,

- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

- * See the License for the specific language governing permissions and

- * limitations under the License.

- *

- * %CopyrightEnd%

- */

-

-#ifdef HAVE_CONFIG_H

-#  include "config.h"

-#endif

-

-#include "sys.h"

-#include "erl_sys_driver.h"

-#include "erl_alloc.h"

-

-static WCHAR *merge_environment(WCHAR *current, WCHAR *add);

-static WCHAR *arg_to_env(WCHAR **arg);

-static WCHAR **env_to_arg(WCHAR *env);

-static WCHAR **find_arg(WCHAR **arg, WCHAR *str);

-static int compare(const void *a, const void *b);

-

-static erts_rwmtx_t environ_rwmtx;
-

-void

-erts_sys_env_init(void)

-{

-    erts_rwmtx_init(&environ_rwmtx, "environ", NIL,
-        ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_GENERIC);

-}

-

-int

-erts_sys_putenv_raw(char *key, char *value)

-{

-    int res;

-    erts_rwmtx_rwlock(&environ_rwmtx);
-    res = (SetEnvironmentVariable((LPCTSTR) key,

-				  (LPCTSTR) value) ? 0 : 1);

-    erts_rwmtx_rwunlock(&environ_rwmtx);
-    return res;

-}

-

-int

-erts_sys_putenv(char *key, char *value)

-{

-    int res;

-    WCHAR *wkey = (WCHAR *) key;

-    WCHAR *wvalue = (WCHAR *) value;

-    erts_rwmtx_rwlock(&environ_rwmtx);
-    res = (SetEnvironmentVariableW(wkey,

-				   wvalue) ? 0 : 1);

-    erts_rwmtx_rwunlock(&environ_rwmtx);
-    return res;

-}

-

-int

-erts_sys_getenv(char *key, char *value, size_t *size)

-{

-    size_t req_size = 0;

-    int res = 0;

-    DWORD new_size;

-    WCHAR *wkey = (WCHAR *) key;

-    WCHAR *wvalue = (WCHAR *) value;

-    DWORD wsize = *size / (sizeof(WCHAR) / sizeof(char));

-

-    SetLastError(0);

-    erts_rwmtx_rlock(&environ_rwmtx);
-    new_size = GetEnvironmentVariableW(wkey,

-				       wvalue,

-				      (DWORD) wsize);

-    res = !new_size && GetLastError() == ERROR_ENVVAR_NOT_FOUND ? -1 : 0;

-    erts_rwmtx_runlock(&environ_rwmtx);
-    if (res < 0)

-	return res;

-    res = new_size > wsize ? 1 : 0;

-    *size = new_size * (sizeof(WCHAR) / sizeof(char));

-    return res;

-}

-int

-erts_sys_getenv__(char *key, char *value, size_t *size)

-{

-    size_t req_size = 0;

-    int res = 0;

-    DWORD new_size;

-

-    SetLastError(0);

-    new_size = GetEnvironmentVariable((LPCTSTR) key,

-				      (LPTSTR) value,

-				      (DWORD) *size);

-    res = !new_size && GetLastError() == ERROR_ENVVAR_NOT_FOUND ? -1 : 0;

-    if (res < 0)

-	return res;

-    res = new_size > *size ? 1 : 0;

-    *size = new_size;

-    return res;

-}

-

-int

-erts_sys_getenv_raw(char *key, char *value, size_t *size)

-{

-    int res;

-    erts_rwmtx_rlock(&environ_rwmtx);
-    res = erts_sys_getenv__(key, value, size);

-    erts_rwmtx_runlock(&environ_rwmtx);
-    return res;

-}

-

-void init_getenv_state(GETENV_STATE *state)

-{

-    erts_rwmtx_rlock(&environ_rwmtx);
-    state->environment_strings = GetEnvironmentStringsW();

-    state->next_string = state->environment_strings;

-}

-

-char *getenv_string(GETENV_STATE *state)

-{

-    ERTS_LC_ASSERT(erts_lc_rwmtx_is_rlocked(&environ_rwmtx));
-    if (state->next_string[0] == L'\0') {

-	return NULL;

-    } else {

-	WCHAR *res = state->next_string;

-	state->next_string += wcslen(res) + 1;

-	return (char *) res;

-    }

-}

-

-void fini_getenv_state(GETENV_STATE *state)

-{

-    FreeEnvironmentStringsW(state->environment_strings);

-    state->environment_strings = state->next_string = NULL;

-    erts_rwmtx_runlock(&environ_rwmtx);
-}

-

-int erts_sys_unsetenv(char *key)

-{

-    int res = 0;

-    WCHAR *wkey = (WCHAR *) key;

-

-    SetLastError(0);

-    erts_rwmtx_rlock(&environ_rwmtx);
-    GetEnvironmentVariableW(wkey,

-                            NULL,

-                            0);

-    if (GetLastError() != ERROR_ENVVAR_NOT_FOUND) {

-        res = (SetEnvironmentVariableW(wkey,

-                                       NULL) ? 0 : 1);

-    }

-    erts_rwmtx_runlock(&environ_rwmtx);
-    return res;

-}

-

-char*

-win_build_environment(char* new_env)

-{

-    if (new_env == NULL) {

-	return NULL;

-    } else {

-	WCHAR *tmp, *merged, *tmp_new;

-

-	tmp_new = (WCHAR *) new_env;

-	

-	erts_rwmtx_rlock(&environ_rwmtx);
-	tmp = GetEnvironmentStringsW();

-	merged = merge_environment(tmp, tmp_new);

-

-	FreeEnvironmentStringsW(tmp);

-	erts_rwmtx_runlock(&environ_rwmtx);
-	return (char *) merged;

-    }

-}

-

-static WCHAR *

-merge_environment(WCHAR *old, WCHAR *add)

-{

-    WCHAR **a_arg = env_to_arg(add);

-    WCHAR **c_arg = env_to_arg(old);

-    WCHAR *ret;

-    int i, j;

-    

-    for(i = 0; c_arg[i] != NULL; ++i)

-	;

-

-    for(j = 0; a_arg[j] != NULL; ++j)

-	;

-

-    c_arg = erts_realloc(ERTS_ALC_T_TMP,

-			 c_arg, (i+j+1) * sizeof(WCHAR *));

-

-    for(j = 0; a_arg[j] != NULL; ++j){

-	WCHAR **tmp;

-	WCHAR *current = a_arg[j];

-	WCHAR *eq_p = wcschr(current,L'=');

-	int unset = (eq_p!=NULL && eq_p[1]==L'\0');

-

-	if ((tmp = find_arg(c_arg, current)) != NULL) {

-	    if (!unset) {

-		*tmp = current;

-	    } else {

-		*tmp = c_arg[--i];

-		c_arg[i] = NULL;

-	    }

-	} else if (!unset) {

-	    c_arg[i++] = current;

-	    c_arg[i] = NULL;

-	}

-    }

-    ret = arg_to_env(c_arg);

-    erts_free(ERTS_ALC_T_TMP, c_arg);

-    erts_free(ERTS_ALC_T_TMP, a_arg);

-    return ret;

-}

-

-static WCHAR**

-find_arg(WCHAR **arg, WCHAR *str)

-{

-    WCHAR *tmp;

-    int len;

-

-    if ((tmp = wcschr(str, L'=')) != NULL) {

-	tmp++;

-	len = tmp - str;

-	while (*arg != NULL){

-	    if (_wcsnicmp(*arg, str, len) == 0){

-		return arg;

-	    }

-	    ++arg;

-	}

-    }

-    return NULL;

-}

-

-static int

-compare(const void *a, const void *b)

-{

-    WCHAR *s1 = *((WCHAR **) a);

-    WCHAR *s2 = *((WCHAR **) b);

-    WCHAR *e1 = wcschr(s1,L'=');

-    WCHAR *e2 = wcschr(s2,L'=');

-    int ret;

-    int len;

-  

-    if(!e1)

-	e1 = s1 + wcslen(s1);

-    if(!e2)

-	e2 = s2 + wcslen(s2);

-  

-    if((e1 - s1) > (e2 - s2))

-	len = (e2 - s2);

-    else

-	len = (e1 - s1);

-  

-    ret = _wcsnicmp(s1,s2,len);

-    if (ret == 0)

-	return ((e1 - s1) - (e2 - s2));

-    else

-	return ret;

-}

-

-static WCHAR**

-env_to_arg(WCHAR *env)

-{

-    WCHAR **ret;

-    WCHAR *tmp;

-    int i;

-    int num_strings = 0;

-

-    for(tmp = env; *tmp != '\0'; tmp += wcslen(tmp)+1) {

-	++num_strings;

-    }

-    ret = erts_alloc(ERTS_ALC_T_TMP, sizeof(WCHAR *) * (num_strings + 1));

-    i = 0;

-    for(tmp = env; *tmp != '\0'; tmp += wcslen(tmp)+1){

-	ret[i++] = tmp;

-    }

-    ret[i] = NULL;

-    return ret;

-}

-

-static WCHAR *

-arg_to_env(WCHAR **arg)

-{

-    WCHAR *block;

-    WCHAR *ptr;

-    int i;

-    int totlen = 1;		/* extra '\0' */

-

-    for(i = 0; arg[i] != NULL; ++i) {

-	totlen += wcslen(arg[i])+1;

-    }

-

-    /* sort the environment vector */

-    qsort(arg, i, sizeof(WCHAR *), &compare);

-

-    if (totlen == 1){

-	block = erts_alloc(ERTS_ALC_T_ENVIRONMENT, 2 * sizeof(WCHAR));

-	block[0] = block[1] = '\0'; 

-    } else {

-	block = erts_alloc(ERTS_ALC_T_ENVIRONMENT, totlen * sizeof(WCHAR));

-	ptr = block;

-	for(i=0; arg[i] != NULL; ++i){

-	    wcscpy(ptr, arg[i]);

-	    ptr += wcslen(ptr)+1;

-	}

-	*ptr = '\0';

-    }

-    return block;

-}

+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 2002-2017. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * %CopyrightEnd%
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include "sys.h"
+#include "erl_sys_driver.h"
+#include "erl_alloc.h"
+
+static erts_osenv_t sysenv_global_env;
+static erts_rwmtx_t sysenv_rwmtx;
+
+static void import_initial_env(void);
+
+void erts_sys_env_init() {
+    erts_rwmtx_init(&sysenv_rwmtx, "environ", NIL,
+        ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_GENERIC);
+
+    erts_osenv_init(&sysenv_global_env);
+    import_initial_env();
+}
+
+const erts_osenv_t *erts_sys_rlock_global_osenv() {
+    erts_rwmtx_rlock(&sysenv_rwmtx);
+    return &sysenv_global_env;
+}
+
+erts_osenv_t *erts_sys_rwlock_global_osenv() {
+    erts_rwmtx_rwlock(&sysenv_rwmtx);
+    return &sysenv_global_env;
+}
+
+void erts_sys_runlock_global_osenv() {
+    erts_rwmtx_runlock(&sysenv_rwmtx);
+}
+
+void erts_sys_rwunlock_global_osenv() {
+    erts_rwmtx_rwunlock(&sysenv_rwmtx);
+}
+
+int erts_sys_explicit_host_getenv(char *key, char *value, size_t *size) {
+    size_t new_size = GetEnvironmentVariableA(key, value, (DWORD)*size);
+
+    if(new_size == 0 && GetLastError() == ERROR_ENVVAR_NOT_FOUND) {
+        return 0;
+    } else if(new_size > *size) {
+        return -1;
+    }
+
+    *size = new_size;
+    return 1;
+}
+
+int erts_sys_explicit_8bit_putenv(char *key, char *value) {
+    WCHAR *wide_key, *wide_value;
+    int key_length, value_length;
+    int result;
+
+    /* Note that we do *NOT* honor the filename encoding flags (+fnu/+fnl)
+     * here; the previous implementation used SetEnvironmentVariableA and
+     * things may break if we step away from that. */
+
+    key_length = MultiByteToWideChar(CP_ACP, 0, key, -1, NULL, 0);
+    value_length = MultiByteToWideChar(CP_ACP, 0, value, -1, NULL, 0);
+
+    /* Report "not found" if either string isn't convertible. */
+    if(key_length == 0 || value_length == 0) {
+        return 0;
+    }
+
+    wide_key = erts_alloc(ERTS_ALC_T_TMP, key_length * sizeof(WCHAR));
+    wide_value = erts_alloc(ERTS_ALC_T_TMP, value_length * sizeof(WCHAR));
+
+    MultiByteToWideChar(CP_ACP, 0, key, -1, wide_key, key_length);
+    MultiByteToWideChar(CP_ACP, 0, value, -1, wide_value, value_length);
+
+    {
+        erts_osenv_data_t env_key, env_value;
+        erts_osenv_t *env;
+
+        env = erts_sys_rwlock_global_osenv();
+
+        /* -1 to exclude the NUL terminator. */
+        env_key.length = (key_length - 1) * sizeof(WCHAR);
+        env_key.data = wide_key;
+
+        env_value.length = (value_length - 1) * sizeof(WCHAR);
+        env_value.data = wide_value;
+
+        result = erts_osenv_put_native(env, &env_key, &env_value);
+        erts_sys_rwunlock_global_osenv();
+    }
+
+    erts_free(ERTS_ALC_T_TMP, wide_key);
+    erts_free(ERTS_ALC_T_TMP, wide_value);
+
+    return result;
+}
+
+int erts_sys_explicit_8bit_getenv(char *key, char *value, size_t *size) {
+    erts_osenv_data_t env_key, env_value;
+    int key_length, value_length, result;
+    WCHAR *wide_key, *wide_value;
+
+    key_length = MultiByteToWideChar(CP_ACP, 0, key, -1, NULL, 0);
+
+    /* Report "not found" if the string isn't convertible. */
+    if(key_length == 0) {
+        return 0;
+    }
+
+    wide_key = erts_alloc(ERTS_ALC_T_TMP, key_length * sizeof(WCHAR));
+    MultiByteToWideChar(CP_ACP, 0, key, -1, wide_key, key_length);
+
+    /* We assume that the worst possible size is twice the output buffer width,
+     * as we could theoretically be on a code page that requires surrogates. */
+    value_length = (*size) * 2;
+    wide_value = erts_alloc(ERTS_ALC_T_TMP, value_length * sizeof(WCHAR));
+
+    {
+        const erts_osenv_t *env = erts_sys_rlock_global_osenv();
+
+        /* -1 to exclude the NUL terminator. */
+        env_key.length = (key_length - 1) * sizeof(WCHAR);
+        env_key.data = wide_key;
+
+        env_value.length = value_length * sizeof(WCHAR);
+        env_value.data = wide_value;
+
+        result = erts_osenv_get_native(env, &env_key, &env_value);
+        erts_sys_runlock_global_osenv();
+    }
+
+    if(result == 1 && env_value.length > 0) {
+        /* This function doesn't NUL-terminate if the provided size is >= 0,
+         * so we pass (*size - 1) to reserve space for it and then do it
+         * manually. */
+        *size = WideCharToMultiByte(CP_ACP, 0, env_value.data,
+            env_value.length / sizeof(WCHAR), value, *size - 1, NULL, NULL);
+
+        if(*size == 0) {
+            if(GetLastError() == ERROR_INSUFFICIENT_BUFFER) {
+                result = -1;
+            } else {
+                result = 0;
+            }
+        }
+    } else {
+        *size = 0;
+    }
+
+    if(*size > 0) {
+        value[*size] = '\0';
+    }
+
+    erts_free(ERTS_ALC_T_TMP, wide_key);
+    erts_free(ERTS_ALC_T_TMP, wide_value);
+
+    return result;
+}
+
+static void import_initial_env(void) {
+    WCHAR *environment_block, *current_variable;
+
+    environment_block = GetEnvironmentStringsW();
+    current_variable = environment_block;
+
+    while(wcslen(current_variable) > 0) {
+        WCHAR *separator_index = wcschr(current_variable, L'=');
+
+        /* We tolerate environment variables starting with '=' as the per-drive
+         * working directories are stored this way. */
+        if(separator_index == current_variable) {
+            separator_index = wcschr(separator_index + 1, L'=');
+        }
+
+        if(separator_index != NULL && separator_index != current_variable) {
+            erts_osenv_data_t env_key, env_value;
+
+            env_key.length = (separator_index - current_variable) * sizeof(WCHAR);
+            env_key.data = current_variable;
+
+            env_value.length = (wcslen(separator_index) - 1) * sizeof(WCHAR);
+            env_value.data = separator_index + 1;
+
+            erts_osenv_put_native(&sysenv_global_env, &env_key, &env_value);
+        }
+
+        current_variable += wcslen(current_variable) + 1;
+    }
+
+    FreeEnvironmentStringsW(environment_block);
+}