hush: fix NOMMU hangs in pseudo_exec_argv. Add forgotted setting

 of signal mask. Reuse same help string in all shells.

function                                             old     new   delta
builtin_exit                                          49      47      -2
pseudo_exec_argv                                     149     145      -4
builtin_help                                          74      63     -11
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-17)             Total: -17 bytes
   text    data     bss     dec     hex filename
 825379     476    7616  833471   cb7bf busybox_old
 825341     476    7616  833433   cb799 busybox_unstripped

4 files changed, 75 insertions, 64 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 1cd205068..fe8c1bed2 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -12230,7 +12230,9 @@ helpcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
         unsigned col;
         unsigned i;
 
-        out1fmt("\nBuilt-in commands:\n-------------------\n");
+        out1fmt("\n"
+                "Built-in commands:\n"
+                "------------------\n");
         for (col = 0, i = 0; i < ARRAY_SIZE(builtintab); i++) {
                 col += out1fmt("%c%s", ((col == 0) ? '\t' : ' '),
                                         builtintab[i].name + 1);
diff --git a/shell/hush.c b/shell/hush.c
index 61db928b2..c38420240 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -363,11 +363,13 @@ struct parse_context {
         /* bitmask of FLAG_xxx, for figuring out valid reserved words */
         int old_flag;
         /* group we are enclosed in:
-         * example 1: "{ { false; ..."
-         * example 2: "if true; then { false; ..."
-         * example 3: "if true; then if false; ..."
-         * when we find closing "}" / "fi" / whatever, we move list_head
-         * into stack->command->group and delete ourself.
+         * example: "if pipe1; pipe2; then pipe3; fi"
+         * when we see "if" or "then", we malloc and copy current context,
+         * and make ->stack point to it. then we parse pipeN.
+         * when closing "then" / fi" / whatever is found,
+         * we move list_head into ->stack->command->group,
+         * copy ->stack into current context, and delete ->stack.
+         * (parsing of { list } and ( list ) doesn't use this method)
          */
         struct parse_context *stack;
 #endif
@@ -532,7 +534,6 @@ static int builtin_wait(char **argv);
 static int builtin_break(char **argv);
 static int builtin_continue(char **argv);
 #endif
-//static int builtin_not_written(char **argv);
 
 /* Table of built-in functions.  They can be forked or not, depending on
  * context: within pipes, they fork.  As simple commands, they do not.
@@ -554,42 +555,44 @@ struct built_in_command {
 /* For now, echo and test are unconditionally enabled.
  * Maybe make it configurable? */
 static const struct built_in_command bltins[] = {
-        BLTIN("."     , builtin_source, "Run commands in a file"),
-        BLTIN(":"     , builtin_true, "No-op"),
-        BLTIN("["     , builtin_test, "Test condition"),
+        BLTIN("."       , builtin_source  , "Run commands in a file"),
+        BLTIN(":"       , builtin_true    , "No-op"),
+        BLTIN("["       , builtin_test    , "Test condition"),
 #if ENABLE_HUSH_JOB
-        BLTIN("bg"    , builtin_fg_bg, "Resume a job in the background"),
+        BLTIN("bg"      , builtin_fg_bg   , "Resume a job in the background"),
 #endif
 #if ENABLE_HUSH_LOOPS
-        BLTIN("break" , builtin_break, "Exit from a loop"),
+        BLTIN("break"   , builtin_break   , "Exit from a loop"),
 #endif
-        BLTIN("cd"    , builtin_cd, "Change directory"),
+        BLTIN("cd"      , builtin_cd      , "Change directory"),
 #if ENABLE_HUSH_LOOPS
         BLTIN("continue", builtin_continue, "Start new loop iteration"),
 #endif
-        BLTIN("echo"  , builtin_echo, "Write to stdout"),
-        BLTIN("eval"  , builtin_eval, "Construct and run shell command"),
-        BLTIN("exec"  , builtin_exec, "Execute command, don't return to shell"),
-        BLTIN("exit"  , builtin_exit, "Exit"),
-        BLTIN("export", builtin_export, "Set environment variable"),
+        BLTIN("echo"    , builtin_echo    , "Write to stdout"),
+        BLTIN("eval"    , builtin_eval    , "Construct and run shell command"),
+        BLTIN("exec"    , builtin_exec    , "Execute command, don't return to shell"),
+        BLTIN("exit"    , builtin_exit    , "Exit"),
+        BLTIN("export"  , builtin_export  , "Set environment variable"),
 #if ENABLE_HUSH_JOB
-        BLTIN("fg"    , builtin_fg_bg, "Bring job into the foreground"),
-        BLTIN("jobs"  , builtin_jobs, "List active jobs"),
-#endif
-        BLTIN("pwd"   , builtin_pwd, "Print current directory"),
-        BLTIN("read"  , builtin_read, "Input environment variable"),
-//      BLTIN("return", builtin_not_written, "Return from a function"),
-        BLTIN("set"   , builtin_set, "Set/unset shell local variables"),
-        BLTIN("shift" , builtin_shift, "Shift positional parameters"),
-        BLTIN("test"  , builtin_test, "Test condition"),
-        BLTIN("trap"  , builtin_trap, "Trap signals"),
-//      BLTIN("ulimit", builtin_not_written, "Control resource limits"),
-        BLTIN("umask" , builtin_umask, "Set file creation mask"),
-        BLTIN("unset" , builtin_unset, "Unset environment variable"),
-        BLTIN("wait"  , builtin_wait, "Wait for process"),
+        BLTIN("fg"      , builtin_fg_bg   , "Bring job into the foreground"),
+#endif
 #if ENABLE_HUSH_HELP
-        BLTIN("help"  , builtin_help, "List shell built-in commands"),
+        BLTIN("help"    , builtin_help    , "List shell built-in commands"),
 #endif
+#if ENABLE_HUSH_JOB
+        BLTIN("jobs"    , builtin_jobs    , "List active jobs"),
+#endif
+        BLTIN("pwd"     , builtin_pwd     , "Print current directory"),
+        BLTIN("read"    , builtin_read    , "Input environment variable"),
+//      BLTIN("return"  , builtin_return  , "Return from a function"),
+        BLTIN("set"     , builtin_set     , "Set/unset shell local variables"),
+        BLTIN("shift"   , builtin_shift   , "Shift positional parameters"),
+        BLTIN("test"    , builtin_test    , "Test condition"),
+        BLTIN("trap"    , builtin_trap    , "Trap signals"),
+//      BLTIN("ulimit"  , builtin_return  , "Control resource limits"),
+        BLTIN("umask"   , builtin_umask   , "Set file creation mask"),
+        BLTIN("unset"   , builtin_unset   , "Unset environment variable"),
+        BLTIN("wait"    , builtin_wait    , "Wait for process"),
 };
 
 
@@ -2117,7 +2120,7 @@ static void restore_redirects(int squirrel[])
 #endif
 static void free_pipe_list(struct pipe *head, int indent);
 
-/* return code is the exit status of the pipe */
+/* Return code is the exit status of the pipe */
 static void free_pipe(struct pipe *pi, int indent)
 {
         char **p;
@@ -2125,7 +2128,7 @@ static void free_pipe(struct pipe *pi, int indent)
         struct redir_struct *r, *rnext;
         int a, i;
 
-        if (pi->stopped_cmds > 0)
+        if (pi->stopped_cmds > 0) /* why? */
                 return;
         debug_printf_clean("%s run pipe: (pid %d)\n", indenter(indent), getpid());
         for (i = 0; i < pi->num_cmds; i++) {
@@ -2216,9 +2219,7 @@ static void pseudo_exec_argv(nommu_save_t *nommu_save,
         char **new_env;
         const struct built_in_command *x;
 
-        /* If a variable is assigned in a forest, and nobody listens,
-         * was it ever really set?
-         */
+        /* Case when we are here: ... | var=val | ... */
         if (!argv[assignment_cnt])
                 _exit(EXIT_SUCCESS);
 
@@ -2239,8 +2240,13 @@ static void pseudo_exec_argv(nommu_save_t *nommu_save,
 #endif
         }
 
-        /*
-         * Check if the command matches any of the builtins.
+        /* On NOMMU, we must never block!
+         * Example: { sleep 99999 | read line } & echo Ok
+         * read builtin will block on read syscall, leaving parent blocked
+         * in vfork. Therefore we can't do this:
+         */
+#if BB_MMU
+        /* Check if the command matches any of the builtins.
          * Depending on context, this might be redundant.  But it's
          * easier to waste a few CPU cycles than it is to figure out
          * if this is one of those cases.
@@ -2249,33 +2255,35 @@ static void pseudo_exec_argv(nommu_save_t *nommu_save,
                 if (strcmp(argv[0], x->cmd) == 0) {
                         debug_printf_exec("running builtin '%s'\n", argv[0]);
                         rcode = x->function(argv);
-                        fflush(stdout);
+                        fflush(NULL);
                         _exit(rcode);
                 }
         }
+#endif
 
-        /* Check if the command matches any busybox applets */
 #if ENABLE_FEATURE_SH_STANDALONE
+        /* Check if the command matches any busybox applets */
         if (strchr(argv[0], '/') == NULL) {
                 int a = find_applet_by_name(argv[0]);
                 if (a >= 0) {
+#if BB_MMU /* see above why on NOMMU it is not allowed */
                         if (APPLET_IS_NOEXEC(a)) {
                                 debug_printf_exec("running applet '%s'\n", argv[0]);
-// is it ok that run_applet_no_and_exit() does exit(), not _exit()?
                                 run_applet_no_and_exit(a, argv);
                         }
-                        /* re-exec ourselves with the new arguments */
+#endif
+                        /* Re-exec ourselves */
                         debug_printf_exec("re-execing applet '%s'\n", argv[0]);
-                        execvp(bb_busybox_exec_path, argv);
+                        sigprocmask(SIG_SETMASK, &G.inherited_set, NULL);
+                        execv(bb_busybox_exec_path, argv);
                         /* If they called chroot or otherwise made the binary no longer
                          * executable, fall through */
                 }
         }
 #endif
 
-        sigprocmask(SIG_SETMASK, &G.inherited_set, NULL);
-
         debug_printf_exec("execing '%s'\n", argv[0]);
+        sigprocmask(SIG_SETMASK, &G.inherited_set, NULL);
         execvp(argv[0], argv);
         bb_perror_msg("can't exec '%s'", argv[0]);
         _exit(EXIT_FAILURE);
@@ -2317,8 +2325,8 @@ static void pseudo_exec(nommu_save_t *nommu_save,
 #endif
         }
 
-        /* Can happen.  See what bash does with ">foo" by itself. */
-        debug_printf("pseudo_exec'ed null command\n");
+        /* Case when we are here: ... | >file */
+        debug_printf_exec("pseudo_exec'ed null command\n");
         _exit(EXIT_SUCCESS);
 }
 
@@ -2569,8 +2577,8 @@ static int checkjobs_and_fg_shell(struct pipe* fg_pipe)
 }
 #endif
 
-/* run_pipe() starts all the jobs, but doesn't wait for anything
- * to finish.  See checkjobs().
+/* Start all the jobs, but don't wait for anything to finish.
+ * See checkjobs().
  *
  * Return code is normally -1, when the caller has to wait for children
  * to finish to determine the exit status of the pipe.  If the pipe
@@ -2588,7 +2596,7 @@ static int checkjobs_and_fg_shell(struct pipe* fg_pipe)
  * cmd || ...  { list } || ...
  * If it is, then we can run cmd as a builtin, NOFORK [do we do this?],
  * or (if SH_STANDALONE) an applet, and we can run the { list }
- * with run_list(). Otherwise, we fork and exec cmd.
+ * with run_list(). If it isn't one of these, we fork and exec cmd.
  *
  * Cases when we must fork:
  * non-single:   cmd | cmd
@@ -3771,7 +3779,7 @@ static FILE *generate_stream_from_string(const char *s)
          * echo OK
          */
 //TODO: pass non-exported variables, traps, and functions
-                execl(CONFIG_BUSYBOX_EXEC_PATH, "hush", "-c", s, NULL);
+                execl(bb_busybox_exec_path, "hush", "-c", s, NULL);
                 _exit(127);
 #endif
         }
@@ -5144,7 +5152,7 @@ static int builtin_fg_bg(char **argv)
  found:
         // TODO: bash prints a string representation
         // of job being foregrounded (like "sleep 1 | cat")
-        if (*argv[0] == 'f') {
+        if (argv[0][0] == 'f') {
                 /* Put the job into the foreground.  */
                 tcsetpgrp(G_interactive_fd, pi->pgrp);
         }
@@ -5162,12 +5170,11 @@ static int builtin_fg_bg(char **argv)
                 if (errno == ESRCH) {
                         delete_finished_bg_job(pi);
                         return EXIT_SUCCESS;
-                } else {
-                        bb_perror_msg("kill (SIGCONT)");
                 }
+                bb_perror_msg("kill (SIGCONT)");
         }
 
-        if (*argv[0] == 'f') {
+        if (argv[0][0] == 'f') {
                 remove_bg_job(pi);
                 return checkjobs_and_fg_shell(pi);
         }
@@ -5180,8 +5187,9 @@ static int builtin_help(char **argv UNUSED_PARAM)
 {
         const struct built_in_command *x;
 
-        printf("\nBuilt-in commands:\n");
-        printf("-------------------\n");
+        printf("\n"
+                "Built-in commands:\n"
+                "------------------\n");
         for (x = bltins; x != &bltins[ARRAY_SIZE(bltins)]; x++) {
                 printf("%s\t%s\n", x->cmd, x->descr);
         }
diff --git a/shell/lash_unused.c b/shell/lash_unused.c
index 90b1f56cf..21ea5471b 100644
--- a/shell/lash_unused.c
+++ b/shell/lash_unused.c
@@ -312,8 +312,9 @@ static int builtin_help(struct child_prog UNUSED_PARAM *dummy)
 {
         const struct built_in_command *x;
 
-        printf("\nBuilt-in commands:\n"
-               "-------------------\n");
+        printf("\n"
+                "Built-in commands:\n"
+                "------------------\n");
         for (x = bltins; x <= &VEC_LAST(bltins); x++) {
                 if (x->descr == NULL)
                         continue;
diff --git a/shell/msh.c b/shell/msh.c
index 5f8c90ef6..da1dc3576 100644
--- a/shell/msh.c
+++ b/shell/msh.c
@@ -35,7 +35,6 @@
 # include <assert.h>
 # define bb_dev_null "/dev/null"
 # define DEFAULT_SHELL "/proc/self/exe"
-# define CONFIG_BUSYBOX_EXEC_PATH "/proc/self/exe"
 # define bb_banner "busybox standalone"
 # define ENABLE_FEATURE_SH_STANDALONE 0
 # define bb_msg_memory_exhausted "memory exhausted"
@@ -3176,8 +3175,9 @@ static int dohelp(struct op *t UNUSED_PARAM, char **args UNUSED_PARAM)
         int col;
         const struct builtincmd *x;
 
-        puts("\nBuilt-in commands:\n"
-             "-------------------");
+        printf("\n"
+                "Built-in commands:\n"
+                "------------------\n");
 
         col = 0;
         x = builtincmds;