setup_environment: code shrink

run_shell: mark as NORETURN
setup_environment, run_shell: add usage comments
login: add FIXME :(

function                                             old     new   delta
UNSPEC_print                                          64      66      +2
sulogin_main                                         509     506      -3
mkfs_minix_main                                     3070    3067      -3
login_main                                          1615    1612      -3
su_main                                              461     448     -13
setup_environment                                    261     206     -55
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/5 up/down: 2/-77)             Total: -75 bytes
   text    data     bss     dec     hex filename
 772578    1051   10724  784353   bf7e1 busybox_old
 772502    1051   10724  784277   bf795 busybox_unstripped

5 files changed, 41 insertions, 21 deletions

diff --git a/include/libbb.h b/include/libbb.h
index a4aa90da3..e5f03517f 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -780,6 +780,7 @@ char *bb_simplify_path(const char *path);
 extern void bb_do_delay(int seconds);
 extern void change_identity(const struct passwd *pw);
 extern const char *change_identity_e2str(const struct passwd *pw);
+extern void run_shell(const char *shell, int loginshell, const char *command, const char **additional_args) ATTRIBUTE_NORETURN;
 extern void run_shell(const char *shell, int loginshell, const char *command, const char **additional_args);
 #if ENABLE_SELINUX
 extern void renew_current_security_context(void);
@@ -790,6 +791,21 @@ extern void setfscreatecon_or_die(security_context_t scontext);
 #endif
 extern void selinux_or_die(void);
 extern int restricted_shell(const char *shell);
+
+/* setup_environment:
+ * if loginshell = 1: cd(pw->pw_dir), clear environment, then set
+ *   TERM=(old value)
+ *   USER=pw->pw_name, LOGNAME=pw->pw_name
+ *   PATH=bb_default_[root_]path
+ *   HOME=pw->pw_dir
+ *   SHELL=shell
+ * else if changeenv = 1:
+ *   if not root (if pw->pw_uid != 0):
+ *     USER=pw->pw_name, LOGNAME=pw->pw_name
+ *   HOME=pw->pw_dir
+ *   SHELL=shell
+ * else does nothing
+ */
 extern void setup_environment(const char *shell, int loginshell, int changeenv, const struct passwd *pw);
 extern int correct_password(const struct passwd *pw);
 /* Returns a ptr to static storage */
diff --git a/libbb/setup_environment.c b/libbb/setup_environment.c
index a6f44f7f0..19a2c6db5 100644
--- a/libbb/setup_environment.c
+++ b/libbb/setup_environment.c
@@ -36,36 +36,35 @@ void setup_environment(const char *shell, int loginshell, int changeenv, const s
                 const char *term;
 
                 /* Change the current working directory to be the home directory
-                 * of the user.  It is a fatal error for this process to be unable
-                 * to change to that directory.  There is no "default" home
-                 * directory.
-                 * Some systems default to HOME=/
-                 */
+                 * of the user */
                 if (chdir(pw->pw_dir)) {
                         xchdir("/");
                         fputs("warning: cannot change to home directory\n", stderr);
                 }
 
-                /* Leave TERM unchanged.  Set HOME, SHELL, USER, LOGNAME, PATH.
+                /* Leave TERM unchanged. Set HOME, SHELL, USER, LOGNAME, PATH.
                    Unset all other environment variables.  */
                 term = getenv("TERM");
                 clearenv();
                 if (term)
                         xsetenv("TERM", term);
-                xsetenv("HOME",    pw->pw_dir);
-                xsetenv("SHELL",   shell);
-                xsetenv("USER",    pw->pw_name);
-                xsetenv("LOGNAME", pw->pw_name);
-                xsetenv("PATH",   (pw->pw_uid ? bb_default_path : bb_default_root_path));
+                xsetenv("PATH", (pw->pw_uid ? bb_default_path : bb_default_root_path));
+                goto shortcut;
+                // No, gcc (4.2.1) is not clever enougn to do it itself.
+                //xsetenv("USER",    pw->pw_name);
+                //xsetenv("LOGNAME", pw->pw_name);
+                //xsetenv("HOME",    pw->pw_dir);
+                //xsetenv("SHELL",   shell);
         }
         else if (changeenv) {
                 /* Set HOME, SHELL, and if not becoming a super-user,
                    USER and LOGNAME.  */
-                xsetenv("HOME",  pw->pw_dir);
-                xsetenv("SHELL", shell);
                 if (pw->pw_uid) {
+ shortcut:
                         xsetenv("USER",    pw->pw_name);
                         xsetenv("LOGNAME", pw->pw_name);
                 }
+                xsetenv("HOME",    pw->pw_dir);
+                xsetenv("SHELL",   shell);
         }
 }
diff --git a/loginutils/login.c b/loginutils/login.c
index 5d5053840..7f8907543 100644
--- a/loginutils/login.c
+++ b/loginutils/login.c
@@ -432,7 +432,9 @@ int login_main(int argc, char **argv)
         tmp = pw->pw_shell;
         if (!tmp || !*tmp)
                 tmp = DEFAULT_SHELL;
+        /* setup_environment params: shell, loginshell, changeenv, pw */
         setup_environment(tmp, 1, !(opt & LOGIN_OPT_p), pw);
+        /* FIXME: login shell = 1 -> 3rd parameter is ignored! */
 
         motd();
 
@@ -463,7 +465,8 @@ int login_main(int argc, char **argv)
          * should it leave SIGINT etc enabled or disabled? */
         signal(SIGINT, SIG_DFL);
 
-        run_shell(tmp, 1, 0, 0);        /* exec the shell finally */
+        /* Exec login shell with no additional parameters */
+        run_shell(tmp, 1, NULL, NULL);
 
-        return EXIT_FAILURE;
+        /* return EXIT_FAILURE; - not reached */
 }
diff --git a/loginutils/su.c b/loginutils/su.c
index b4681fb6a..123907e28 100644
--- a/loginutils/su.c
+++ b/loginutils/su.c
@@ -36,7 +36,7 @@ int su_main(int argc, char **argv)
         /* get user if specified */
         if (argc) {
                 opt_username = argv[0];
-//              argc--;
+                //argc--; - not used below anyway
                 argv++;
         }
 
@@ -86,18 +86,19 @@ int su_main(int argc, char **argv)
                    compromise the account by allowing access with a standard
                    shell.  */
                 bb_error_msg("using restricted shell");
-                opt_shell = 0;
+                opt_shell = NULL;
         }
 #endif
         if (!opt_shell)
                 opt_shell = pw->pw_shell;
 
         change_identity(pw);
+        /* setup_environment params: shell, loginshell, changeenv, pw */
         setup_environment(opt_shell, flags & SU_OPT_l, !(flags & SU_OPT_mp), pw);
         USE_SELINUX(set_current_security_context(NULL);)
 
         /* Never returns */
         run_shell(opt_shell, flags & SU_OPT_l, opt_command, (const char**)argv);
 
-        return EXIT_FAILURE;
+        /* return EXIT_FAILURE; - not reached */
 }
diff --git a/loginutils/sulogin.c b/loginutils/sulogin.c
index 5f0a4081d..5c73bda93 100644
--- a/loginutils/sulogin.c
+++ b/loginutils/sulogin.c
@@ -112,14 +112,15 @@ int sulogin_main(int argc, char **argv)
         USE_SELINUX(renew_current_security_context());
 
         shell = getenv("SUSHELL");
-        if (!shell) shell = getenv("sushell");
+        if (!shell)
+                shell = getenv("sushell");
         if (!shell) {
                 shell = "/bin/sh";
                 if (pwd->pw_shell[0])
                         shell = pwd->pw_shell;
         }
-        run_shell(shell, 1, 0, 0);
-        /* never returns */
+        /* Exec login shell with no additional parameters. Never returns. */
+        run_shell(shell, 1, NULL, NULL);
 
 auth_error:
         bb_error_msg_and_die("no password entry for 'root'");