Win32: don't copy the environment twice when spawning child processes

When spawning child processes via start_command(), the environment and all
environment entries are copied twice. First by make_augmented_environ /
copy_environ to merge with child_process.env. Then a second time by
make_environment_block to create a sorted environment block string as
required by CreateProcess.

Move the merge logic to make_environment_block so that we only need to copy
the environment once. This changes semantics of the env parameter: it now
expects a delta (such as child_process.env) rather than a full environment.
This is not a problem as the parameter is only used by start_command()
(all other callers previously passed char **environ, and now pass NULL).

The merge logic no longer xstrdup()s the environment strings, so do_putenv
must not free them. Add a parameter to distinguish this from normal putenv.

Remove the now unused make_augmented_environ / free_environ API.

Signed-off-by: Karsten Blees <[email protected]>

Author: kblees

compat/mingw.c

@@ -759,7 +759,7 @@ static int lookupenv(char **env, const char *name, size_t nmln)
 /*
  * If name contains '=', then sets the variable, otherwise it unsets it
  */
-static char **do_putenv(char **env, const char *name)
+static char **do_putenv(char **env, const char *name, int free_old)
 {
 	char *eq = strchrnul(name, '=');
 	int i = lookupenv(env, name, eq-name);
@@ -774,7 +774,8 @@ static char **do_putenv(char **env, const char *name)
 		}
 	}
 	else {
-		free(env[i]);
+		if (free_old)
+			free(env[i]);
 		if (*eq)
 			env[i] = (char*) name;
 		else
@@ -803,7 +804,7 @@ char *mingw_getenv(const char *name)
 
 int mingw_putenv(const char *namevalue)
 {
-	environ = do_putenv(environ, namevalue);
+	environ = do_putenv(environ, namevalue, 1);
 	return 0;
 }
 
@@ -996,21 +997,30 @@ static char *path_lookup(const char *cmd, char **path, int exe_only)
 }
 
 /*
- * Create environment block suitable for CreateProcess.
+ * Create environment block suitable for CreateProcess. Merges current
+ * process environment and the supplied environment changes.
  */
-static wchar_t *make_environment_block(char **env)
+static wchar_t *make_environment_block(char **deltaenv)
 {
 	wchar_t *wenvblk = NULL;
 	int count = 0;
 	char **e, **tmpenv;
 	int size = 0, wenvsz = 0, wenvpos = 0;
 
-	for (e = env; *e; e++)
+	while (environ[count])
 		count++;
 
-	/* environment must be sorted */
+	/* copy the environment */
 	tmpenv = xmalloc(sizeof(*tmpenv) * (count + 1));
-	memcpy(tmpenv, env, sizeof(*tmpenv) * (count + 1));
+	memcpy(tmpenv, environ, sizeof(*tmpenv) * (count + 1));
+
+	/* merge supplied environment changes into the temporary environment */
+	for (e = deltaenv; e && *e; e++)
+		tmpenv = do_putenv(tmpenv, *e, 0);
+
+	/* environment must be sorted */
+	for (count = 0; tmpenv[count]; )
+		count++;
 	qsort(tmpenv, count, sizeof(*tmpenv), compareenv);
 
 	/* create environment block from temporary environment */
@@ -1033,7 +1043,7 @@ struct pinfo_t {
 struct pinfo_t *pinfo = NULL;
 CRITICAL_SECTION pinfo_cs;
 
-static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **env,
+static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaenv,
 			      const char *dir,
 			      int prepend_cmd, int fhin, int fhout, int fherr)
 {
@@ -1101,8 +1111,7 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **env,
 	xutftowcs(wargs, args.buf, 2 * args.len + 1);
 	strbuf_release(&args);
 
-	if (env)
-		wenvblk = make_environment_block(env);
+	wenvblk = make_environment_block(deltaenv);
 
 	memset(&pi, 0, sizeof(pi));
 	ret = CreateProcessW(wcmd, wargs, NULL, NULL, TRUE, flags,
@@ -1140,10 +1149,10 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **env,
 
 static pid_t mingw_spawnv(const char *cmd, const char **argv, int prepend_cmd)
 {
-	return mingw_spawnve_fd(cmd, argv, environ, NULL, prepend_cmd, 0, 1, 2);
+	return mingw_spawnve_fd(cmd, argv, NULL, NULL, prepend_cmd, 0, 1, 2);
 }
 
-pid_t mingw_spawnvpe(const char *cmd, const char **argv, char **env,
+pid_t mingw_spawnvpe(const char *cmd, const char **argv, char **deltaenv,
 		     const char *dir,
 		     int fhin, int fhout, int fherr)
 {
@@ -1167,14 +1176,14 @@ pid_t mingw_spawnvpe(const char *cmd, const char **argv, char **env,
 				pid = -1;
 			}
 			else {
-				pid = mingw_spawnve_fd(iprog, argv, env, dir, 1,
+				pid = mingw_spawnve_fd(iprog, argv, deltaenv, dir, 1,
 						       fhin, fhout, fherr);
 				free(iprog);
 			}
 			argv[0] = argv0;
 		}
 		else
-			pid = mingw_spawnve_fd(prog, argv, env, dir, 0,
+			pid = mingw_spawnve_fd(prog, argv, deltaenv, dir, 0,
 					       fhin, fhout, fherr);
 		free(prog);
 	}
@@ -1265,41 +1274,6 @@ int mingw_kill(pid_t pid, int sig)
 	return -1;
 }
 
-static char **copy_environ(void)
-{
-	char **env;
-	int i = 0;
-	while (environ[i])
-		i++;
-	env = xmalloc((i+1)*sizeof(*env));
-	for (i = 0; environ[i]; i++)
-		env[i] = xstrdup(environ[i]);
-	env[i] = NULL;
-	return env;
-}
-
-void free_environ(char **env)
-{
-	int i;
-	for (i = 0; env[i]; i++)
-		free(env[i]);
-	free(env);
-}
-
-/*
- * Copies global environ and adjusts variables as specified by vars.
- */
-char **make_augmented_environ(const char *const *vars)
-{
-	char **env = copy_environ();
-
-	while (*vars) {
-		const char *v = *vars++;
-		env = do_putenv(env, strchr(v, '=') ? xstrdup(v) : v);
-	}
-	return env;
-}
-
 /*
  * Note, this isn't a complete replacement for getaddrinfo. It assumes
  * that service contains a numerical port, or that it is null. It

compat/mingw.h

@@ -335,12 +335,6 @@ void mingw_open_html(const char *path);
 void mingw_mark_as_git_dir(const char *dir);
 #define mark_as_git_dir mingw_mark_as_git_dir
 
-/*
- * helpers
- */
-
-char **make_augmented_environ(const char *const *vars);
-void free_environ(char **env);
 
 /**
  * Converts UTF-8 encoded string to UTF-16LE.

run-command.c

@@ -454,7 +454,6 @@ int start_command(struct child_process *cmd)
 {
 	int fhin = 0, fhout = 1, fherr = 2;
 	const char **sargv = cmd->argv;
-	char **env = environ;
 
 	if (cmd->no_stdin)
 		fhin = open("/dev/null", O_RDWR);
@@ -479,25 +478,20 @@ int start_command(struct child_process *cmd)
 	else if (cmd->out > 1)
 		fhout = dup(cmd->out);
 
-	if (cmd->env)
-		env = make_augmented_environ(cmd->env);
-
 	if (cmd->git_cmd) {
 		cmd->argv = prepare_git_cmd(cmd->argv);
 	} else if (cmd->use_shell) {
 		cmd->argv = prepare_shell_cmd(cmd->argv);
 	}
 
-	cmd->pid = mingw_spawnvpe(cmd->argv[0], cmd->argv, env, cmd->dir,
-				  fhin, fhout, fherr);
+	cmd->pid = mingw_spawnvpe(cmd->argv[0], cmd->argv, (char**) cmd->env,
+			cmd->dir, fhin, fhout, fherr);
 	failed_errno = errno;
 	if (cmd->pid < 0 && (!cmd->silent_exec_failure || errno != ENOENT))
 		error("cannot spawn %s: %s", cmd->argv[0], strerror(errno));
 	if (cmd->clean_on_exit && cmd->pid >= 0)
 		mark_child_for_cleanup(cmd->pid);
 
-	if (cmd->env)
-		free_environ(env);
 	if (cmd->git_cmd)
 		free(cmd->argv);