hush: replace signal handling machinery

With new version of signal handling, read builtin should be less buggy
wrt signals.

function                                             old     new   delta
install_sighandlers                                    -     121    +121
switch_off_special_sigs                                -      84     +84
pick_sighandler                                        -      58     +58
install_special_sighandlers                            -      47     +47
builtin_wait                                         284     319     +35
record_pending_signo                                   -      21     +21
execvp_or_die                                         43      48      +5
file_get                                             290     288      -2
run_list                                            1004     998      -6
static.zero_timespec                                   8       -      -8
sigprocmask_set                                       14       -     -14
sigwaitinfo                                           23       -     -23
record_signal                                         23       -     -23
__GI_sigwaitinfo                                      23       -     -23
sigtimedwait                                          25       -     -25
builtin_trap                                         417     392     -25
__GI_sigtimedwait                                     25       -     -25
hush_main                                           1003     965     -38
check_and_run_traps                                  263     217     -46
__rt_sigtimedwait                                     52       -     -52
reset_traps_to_defaults                              213     126     -87
init_sigmasks                                        198       -    -198
builtin_read                                         536     197    -339
------------------------------------------------------------------------------
(add/remove: 5/10 grow/shrink: 2/7 up/down: 371/-934)        Total: -563 bytes
   text	   data	    bss	    dec	    hex	filename
 903075	    936	  17736	 921747	  e1093	busybox_old
 902547	    936	  17736	 921219	  e0e83	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 278 insertions, 232 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 509bd415b..b2c3a752e 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -106,6 +106,10 @@
 # define PIPE_BUF 4096  /* amount of buffering in a pipe */
 #endif
 
+/* Not every libc has sighandler_t. Fix it */
+typedef void (*hush_sighandler_t)(int);
+#define sighandler_t hush_sighandler_t
+
 //config:config HUSH
 //config:       bool "hush"
 //config:       default y
@@ -764,7 +768,6 @@ struct globals {
         smalluint last_exitcode;
         /* are global_argv and global_argv[1..n] malloced? (note: not [0]) */
         smalluint global_args_malloced;
-        smalluint inherited_set_is_saved;
         /* how many non-NULL argv's we have. NB: $# + 1 */
         int global_argc;
         char **global_argv;
@@ -794,21 +797,20 @@ struct globals {
 #endif
         /* Which signals have non-DFL handler (even with no traps set)?
          * Set at the start to:
-         * (SIGQUIT + maybe SPECIAL_INTERACTIVE_SIGS + maybe SPECIAL_JOB_SIGS)
+         * (SIGQUIT + maybe SPECIAL_INTERACTIVE_SIGS + maybe SPECIAL_JOBSTOP_SIGS)
          * SPECIAL_INTERACTIVE_SIGS are cleared after fork.
+         * The rest is cleared right before execv syscalls.
          * Other than these two times, never modified.
          */
         unsigned special_sig_mask;
+#if ENABLE_HUSH_JOB
+        unsigned fatal_sig_mask;
+#define G_fatal_sig_mask G.fatal_sig_mask
+#else
+#define G_fatal_sig_mask 0
+#endif
         char **traps; /* char *traps[NSIG] */
-        /* Signal mask on the entry to the (top-level) shell. Never modified. */
-        sigset_t inherited_set;
-        /* Starts equal to inherited_set,
-         * but shell-special signals are added and SIGCHLD is removed.
-         * When a trap is set/cleared, signal is added to/removed from it:
-         */
-        sigset_t blocked_set;
-        /* Used by read() */
-        sigset_t detected_set;
+        sigset_t pending_set;
 #if HUSH_DEBUG
         unsigned long memleak_value;
         int debug_indent;
@@ -1337,8 +1339,8 @@ static void restore_G_args(save_arg_t *sv, char **argv)
  * (What happens to signals which are IGN on shell start?)
  * (What happens with signal mask on shell start?)
  *
- * Implementation in hush
- * ======================
+ * Old implementation
+ * ==================
  * We use in-kernel pending signal mask to determine which signals were sent.
  * We block all signals which we don't want to take action immediately,
  * i.e. we block all signals which need to have special handling as described
@@ -1369,6 +1371,49 @@ static void restore_G_args(save_arg_t *sv, char **argv)
  * Standard says "When a subshell is entered, traps that are not being ignored
  * are set to the default actions". bash interprets it so that traps which
  * are set to '' (ignore) are NOT reset to defaults. We do the same.
+ *
+ * Problem: the above approach makes it unwieldy to catch signals while
+ * we are in read builtin, of while we read commands from stdin:
+ * masked signals are not visible!
+ *
+ * New implementation
+ * ==================
+ * We record each signal we are interested in by installing signal handler
+ * for them - a bit like emulating kernel pending signal mask in userspace.
+ * We are interested in: signals which need to have special handling
+ * as described above, and all signals which have traps set.
+ * Signals are rocorded in pending_set.
+ * After each pipe execution, we extract any pending signals
+ * and act on them.
+ *
+ * unsigned special_sig_mask: a mask of shell-special signals.
+ * unsigned fatal_sig_mask: a mask of signals on which we restore tty pgrp.
+ * char *traps[sig] if trap for sig is set (even if it's '').
+ * sigset_t pending_set: set of sigs we received.
+ *
+ * "trap - SIGxxx":
+ *    if sig is in special_sig_mask, set handler back to:
+ *        record_pending_signo, or to IGN if it's a tty stop signal
+ *    if sig is in fatal_sig_mask, set handler back to sigexit.
+ *    else: set handler back to SIG_DFL
+ * "trap 'cmd' SIGxxx":
+ *    set handler to record_pending_signo.
+ * "trap '' SIGxxx":
+ *    set handler to SIG_IGN.
+ * after [v]fork, if we plan to be a shell:
+ *    set signals with special interactive handling to SIG_DFL
+ *    (because child shell is not interactive),
+ *    unset all traps except '' (note: regardless of child shell's type - {}, (), etc)
+ * after [v]fork, if we plan to exec:
+ *    POSIX says fork clears pending signal mask in child - no need to clear it.
+ *
+ * To make wait builtin interruptible, we handle SIGCHLD as special signal,
+ * otherwise (if we leave it SIG_DFL) sigsuspend in wait builtin will not wake up on it.
+ *
+ * Note (compat):
+ * Standard says "When a subshell is entered, traps that are not being ignored
+ * are set to the default actions". bash interprets it so that traps which
+ * are set to '' (ignore) are NOT reset to defaults. We do the same.
  */
 enum {
         SPECIAL_INTERACTIVE_SIGS = 0
@@ -1376,26 +1421,25 @@ enum {
                 | (1 << SIGINT)
                 | (1 << SIGHUP)
                 ,
-        SPECIAL_JOB_SIGS = 0
+        SPECIAL_JOBSTOP_SIGS = 0
 #if ENABLE_HUSH_JOB
                 | (1 << SIGTTIN)
                 | (1 << SIGTTOU)
                 | (1 << SIGTSTP)
 #endif
+                ,
 };
 
-static void sigprocmask_set(sigset_t *set)
+static void record_pending_signo(int sig)
 {
-        sigprocmask(SIG_SETMASK, set, NULL);
-}
-
+        sigaddset(&G.pending_set, sig);
 #if ENABLE_HUSH_FAST
-static void SIGCHLD_handler(int sig UNUSED_PARAM)
-{
-        G.count_SIGCHLD++;
+        if (sig == SIGCHLD) {
+                G.count_SIGCHLD++;
 //bb_error_msg("[%d] SIGCHLD_handler: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
-}
+        }
 #endif
+}
 
 #if ENABLE_HUSH_JOB
 
@@ -1433,6 +1477,31 @@ static void sigexit(int sig)
 
 #endif
 
+static sighandler_t pick_sighandler(unsigned sig)
+{
+        sighandler_t handler = SIG_DFL;
+        if (sig < sizeof(unsigned)*8) {
+                unsigned sigmask = (1 << sig);
+
+#if ENABLE_HUSH_JOB
+                /* sig is fatal? */
+                if (G_fatal_sig_mask & sigmask)
+                        handler = sigexit;
+#endif
+                /* sig has special handling? */
+                else if (G.special_sig_mask & sigmask)
+                        handler = record_pending_signo;
+                        /* TTIN/TTOU/TSTS can't be set to record_pending_signo
+                         * in order to ignore them: they will be raised
+                         * in an endless loop then when we try to do some
+                         * terminal ioctls! We do nave to _ignore_ these.
+                         */
+                        if (SPECIAL_JOBSTOP_SIGS & sigmask)
+                                handler = SIG_IGN;
+        }
+        return handler;
+}
+
 /* Restores tty foreground process group, and exits. */
 static void hush_exit(int exitcode) NORETURN;
 static void hush_exit(int exitcode)
@@ -1478,39 +1547,30 @@ static void hush_exit(int exitcode)
 }
 
 
-static int check_and_run_traps(int sig)
+//TODO: return a mask of ALL handled sigs?
+static int check_and_run_traps(void)
 {
-        /* I want it in rodata, not in bss.
-         * gcc 4.2.1 puts it in rodata only if it has { 0, 0 }
-         * initializer. But other compilers may still use bss.
-         * TODO: find more portable solution.
-         */
-        static const struct timespec zero_timespec = { 0, 0 };
-        smalluint save_rcode;
         int last_sig = 0;
 
-        if (sig)
-                goto got_sig;
-
         while (1) {
-                if (!sigisemptyset(&G.detected_set)) {
-                        sig = 0;
-                        do {
-                                sig++;
-                                if (sigismember(&G.detected_set, sig)) {
-                                        sigdelset(&G.detected_set, sig);
-                                        goto got_sig;
-                                }
-                        } while (sig < NSIG);
-                }
+                int sig;
 
-                sig = sigtimedwait(&G.blocked_set, NULL, &zero_timespec);
-                if (sig <= 0)
+                if (sigisemptyset(&G.pending_set))
                         break;
+                sig = 0;
+                do {
+                        sig++;
+                        if (sigismember(&G.pending_set, sig)) {
+                                sigdelset(&G.pending_set, sig);
+                                goto got_sig;
+                        }
+                } while (sig < NSIG);
+                break;
  got_sig:
                 if (G.traps && G.traps[sig]) {
                         if (G.traps[sig][0]) {
                                 /* We have user-defined handler */
+                                smalluint save_rcode;
                                 char *argv[3];
                                 /* argv[0] is unused */
                                 argv[1] = G.traps[sig];
@@ -1524,12 +1584,6 @@ static int check_and_run_traps(int sig)
                 }
                 /* not a trap: special action */
                 switch (sig) {
-#if ENABLE_HUSH_FAST
-                case SIGCHLD:
-                        G.count_SIGCHLD++;
-//bb_error_msg("[%d] check_and_run_traps: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
-                        break;
-#endif
                 case SIGINT:
                         /* Builtin was ^C'ed, make it look prettier: */
                         bb_putchar('\n');
@@ -1551,11 +1605,21 @@ static int check_and_run_traps(int sig)
                         sigexit(SIGHUP);
                 }
 #endif
+#if ENABLE_HUSH_FAST
+                case SIGCHLD:
+                        G.count_SIGCHLD++;
+//bb_error_msg("[%d] check_and_run_traps: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
+                        /* Note:
+                         * We dont do 'last_sig = sig' here -> NOT returning this sig.
+                         * This simplifies wait builtin a bit.
+                         */
+                        break;
+#endif
                 default: /* ignored: */
                         /* SIGTERM, SIGQUIT, SIGTTIN, SIGTTOU, SIGTSTP */
-                        /* note:
-                         * we dont do 'last_sig = sig' here -> NOT returning this sig.
-                         * example: wait is not interrupted by TERM
+                        /* Note:
+                         * We dont do 'last_sig = sig' here -> NOT returning this sig.
+                         * Example: wait is not interrupted by TERM
                          * in interactive shell, because TERM is ignored.
                          */
                         break;
@@ -1948,7 +2012,7 @@ static void get_user_input(struct in_str *i)
                  * only after <Enter>. (^C will work) */
                 r = read_line_input(G.line_input_state, prompt_str, G.user_input_buf, CONFIG_FEATURE_EDITING_MAX_LEN-1, /*timeout*/ -1);
                 /* catch *SIGINT* etc (^C is handled by read_line_input) */
-                check_and_run_traps(0);
+                check_and_run_traps();
         } while (r == 0 || G.flag_SIGINT); /* repeat if ^C or SIGINT */
         i->eof_flag = (r < 0);
         if (i->eof_flag) { /* EOF/error detected */
@@ -1964,7 +2028,7 @@ static void get_user_input(struct in_str *i)
                          * $ <[enter], repeatedly...>
                          * Without check_and_run_traps, handler never runs.
                          */
-                        check_and_run_traps(0);
+                        check_and_run_traps();
                         fputs(prompt_str, stdout);
                 }
                 fflush_all();
@@ -5368,6 +5432,25 @@ void re_execute_shell(char ***to_free, const char *s,
                 char *g_argv0, char **g_argv,
                 char **builtin_argv) NORETURN;
 
+static void switch_off_special_sigs(unsigned mask)
+{
+        unsigned sig = 0;
+        while ((mask >>= 1) != 0) {
+                sig++;
+                if (!(mask & 1))
+                        continue;
+                if (G.traps) {
+                        if (G.traps[sig] && !G.traps[sig][0])
+                                /* trap is '', has to remain SIG_IGN */
+                                continue;
+                        free(G.traps[sig]);
+                        G.traps[sig] = NULL;
+                }
+                /* We are here only if no trap or trap was not '' */
+                signal(sig, SIG_DFL);
+        }
+}
+
 static void reset_traps_to_defaults(void)
 {
         /* This function is always called in a child shell
@@ -5381,44 +5464,35 @@ static void reset_traps_to_defaults(void)
          * Testcase: (while :; do :; done) + ^Z should background.
          * Same goes for SIGTERM, SIGHUP, SIGINT.
          */
-        if (!G.traps && !(G.special_sig_mask & SPECIAL_INTERACTIVE_SIGS))
-                return; /* already no traps and no SPECIAL_INTERACTIVE_SIGS */
-
-        /* Switching off SPECIAL_INTERACTIVE_SIGS.
-         * Stupid. It can be done with *single* &= op, but we can't use
-         * the fact that G.blocked_set is implemented as a bitmask
-         * in libc... */
-        mask = SPECIAL_INTERACTIVE_SIGS;
-        sig = 0;
-        while ((mask >>= 1) != 0) {
-                sig++;
-                if (mask & 1) {
-                        /* Careful. Only if no trap or trap is not "" */
-                        if (!G.traps || !G.traps[sig] || G.traps[sig][0])
-                                sigdelset(&G.blocked_set, sig);
-                }
-        }
-        /* Our homegrown sig mask is saner to work with :) */
+        mask = (G.special_sig_mask & SPECIAL_INTERACTIVE_SIGS) | G_fatal_sig_mask;
+        if (!G.traps && !mask)
+                return; /* already no traps and no special sigs */
+
+        /* Switch off special sigs */
+        switch_off_special_sigs(mask);
+#if ENABLE_HUSH_JOB
+        G_fatal_sig_mask = 0;
+#endif
         G.special_sig_mask &= ~SPECIAL_INTERACTIVE_SIGS;
+        /* SIGQUIT and maybe SPECIAL_JOBSTOP_SIGS remain set in G.special_sig_mask */
 
-        /* Resetting all traps to default except empty ones */
-        mask = G.special_sig_mask;
-        if (G.traps) for (sig = 0; sig < NSIG; sig++, mask >>= 1) {
-                if (!G.traps[sig] || !G.traps[sig][0])
-                        continue;
+        if (!G.traps)
+                return;
+
+        /* Reset all sigs to default except ones with empty traps */
+        for (sig = 0; sig < NSIG; sig++) {
+                if (!G.traps[sig])
+                        continue; /* no trap: nothing to do */
+                if (!G.traps[sig][0])
+                        continue; /* empty trap: has to remain SIG_IGN */
+                /* sig has non-empty trap, reset it: */
                 free(G.traps[sig]);
                 G.traps[sig] = NULL;
-                /* There is no signal for 0 (EXIT) */
+                /* There is no signal for trap 0 (EXIT) */
                 if (sig == 0)
                         continue;
-                /* There was a trap handler, we just removed it.
-                 * But if sig still has non-DFL handling,
-                 * we should not unblock the sig. */
-                if (mask & 1)
-                        continue;
-                sigdelset(&G.blocked_set, sig);
+                signal(sig, pick_sighandler(sig));
         }
-        sigprocmask_set(&G.blocked_set);
 }
 
 #else /* !BB_MMU */
@@ -5463,6 +5537,7 @@ static void re_execute_shell(char ***to_free, const char *s,
                 for (sig = 1; sig < NSIG; sig++) {
                         if (G.traps[sig] && !G.traps[sig][0])
                                 empty_trap_mask |= 1LL << sig;
+///vda: optimize
                 }
         }
 
@@ -5548,7 +5623,7 @@ static void re_execute_shell(char ***to_free, const char *s,
 
  do_exec:
         debug_printf_exec("re_execute_shell pid:%d cmd:'%s'\n", getpid(), s);
-        sigprocmask_set(&G.inherited_set);
+        switch_off_special_sigs(G.special_sig_mask & SPECIAL_JOBSTOP_SIGS);
         execve(bb_busybox_exec_path, argv, pp);
         /* Fallback. Useful for init=/bin/hush usage etc */
         if (argv[0][0] == '/')
@@ -6202,7 +6277,7 @@ static void execvp_or_die(char **argv) NORETURN;
 static void execvp_or_die(char **argv)
 {
         debug_printf_exec("execing '%s'\n", argv[0]);
-        sigprocmask_set(&G.inherited_set);
+        switch_off_special_sigs(G.special_sig_mask & SPECIAL_JOBSTOP_SIGS);
         execvp(argv[0], argv);
         bb_perror_msg("can't execute '%s'", argv[0]);
         _exit(127); /* bash compat */
@@ -6334,7 +6409,7 @@ static NOINLINE void pseudo_exec_argv(nommu_save_t *nommu_save,
 # endif
                         /* Re-exec ourselves */
                         debug_printf_exec("re-execing applet '%s'\n", argv[0]);
-                        sigprocmask_set(&G.inherited_set);
+                        switch_off_special_sigs(G.special_sig_mask & SPECIAL_JOBSTOP_SIGS);
                         execv(bb_busybox_exec_path, argv);
                         /* If they called chroot or otherwise made the binary no longer
                          * executable, fall through */
@@ -7033,9 +7108,6 @@ static NOINLINE int run_pipe(struct pipe *pi)
                         if (setup_redirects(command, NULL))
                                 _exit(1);
 
-                        /* Restore default handlers just prior to exec */
-                        /*signal(SIGCHLD, SIG_DFL); - so far we don't have any handlers */
-
                         /* Stores to nommu_save list of env vars putenv'ed
                          * (NOMMU, on MMU we don't need that) */
                         /* cast away volatility... */
@@ -7313,7 +7385,7 @@ static int run_list(struct pipe *pi)
                                  * and we don't need to wait for anything. */
                                 G.last_exitcode = rcode;
                                 debug_printf_exec(": builtin/func exitcode %d\n", rcode);
-                                check_and_run_traps(0);
+                                check_and_run_traps();
 #if ENABLE_HUSH_LOOPS
                                 /* Was it "break" or "continue"? */
                                 if (G.flag_break_continue) {
@@ -7345,7 +7417,7 @@ static int run_list(struct pipe *pi)
                                 /* even bash 3.2 doesn't do that well with nested bg:
                                  * try "{ { sleep 10; echo DEEP; } & echo HERE; } &".
                                  * I'm NOT treating inner &'s as jobs */
-                                check_and_run_traps(0);
+                                check_and_run_traps();
 #if ENABLE_HUSH_JOB
                                 if (G.run_list_level == 1)
                                         insert_bg_job(pi);
@@ -7360,13 +7432,13 @@ static int run_list(struct pipe *pi)
                                         /* Waits for completion, then fg's main shell */
                                         rcode = checkjobs_and_fg_shell(pi);
                                         debug_printf_exec(": checkjobs_and_fg_shell exitcode %d\n", rcode);
-                                        check_and_run_traps(0);
+                                        check_and_run_traps();
                                 } else
 #endif
                                 { /* This one just waits for completion */
                                         rcode = checkjobs(pi);
                                         debug_printf_exec(": checkjobs exitcode %d\n", rcode);
-                                        check_and_run_traps(0);
+                                        check_and_run_traps();
                                 }
                                 G.last_exitcode = rcode;
                         }
@@ -7437,58 +7509,61 @@ static int run_and_free_list(struct pipe *pi)
 }
 
 
+static void install_sighandlers(unsigned mask)
+{
+        sighandler_t old_handler;
+        unsigned sig = 0;
+        while ((mask >>= 1) != 0) {
+                sig++;
+                if (!(mask & 1))
+                        continue;
+                old_handler = signal(sig, pick_sighandler(sig));
+                /* POSIX allows shell to re-enable SIGCHLD
+                 * even if it was SIG_IGN on entry.
+                 * Therefore we skip IGN check for it:
+                 */
+                if (sig == SIGCHLD)
+                        continue;
+                if (old_handler == SIG_IGN) {
+                        /* oops... restore back to IGN, and record this fact */
+                        signal(sig, old_handler);
+                        if (!G.traps)
+                                G.traps = xzalloc(sizeof(G.traps[0]) * NSIG);
+                        free(G.traps[sig]);
+                        G.traps[sig] = xzalloc(1); /* == xstrdup(""); */
+                }
+        }
+}
+
 /* Called a few times only (or even once if "sh -c") */
-static void init_sigmasks(void)
+static void install_special_sighandlers(void)
 {
-        unsigned sig;
         unsigned mask;
 
-        /* POSIX allows shell to re-enable SIGCHLD
-         * even if it was SIG_IGN on entry */
-        if (!G.inherited_set_is_saved) {
-#if ENABLE_HUSH_FAST
-                signal(SIGCHLD, SIGCHLD_handler);
-#else
-                signal(SIGCHLD, SIG_DFL);
-#endif
-                sigprocmask(SIG_SETMASK, NULL, &G.blocked_set);
-                G.inherited_set = G.blocked_set;
-        }
+        if (G.special_sig_mask != 0)
+                return;
 
         /* Which signals are shell-special? */
-        mask = (1 << SIGQUIT);
+        mask = (1 << SIGQUIT) | (1 << SIGCHLD);
         if (G_interactive_fd) {
                 mask |= SPECIAL_INTERACTIVE_SIGS;
                 if (G_saved_tty_pgrp) /* we have ctty, job control sigs work */
-                        mask |= SPECIAL_JOB_SIGS;
+                        mask |= SPECIAL_JOBSTOP_SIGS;
         }
         G.special_sig_mask = mask;
 
-        /* Block them. And unblock SIGCHLD */
-        sig = 0;
-        while ((mask >>= 1) != 0) {
-                sig++;
-                if (mask & 1)
-                        sigaddset(&G.blocked_set, sig);
-        }
-        sigdelset(&G.blocked_set, SIGCHLD);
-
-        if (memcmp(&G.inherited_set, &G.blocked_set, sizeof(G.inherited_set)) != 0)
-                sigprocmask_set(&G.blocked_set);
-
-        G.inherited_set_is_saved = 1;
+        install_sighandlers(mask);
 }
 
 #if ENABLE_HUSH_JOB
 /* helper */
 /* Set handlers to restore tty pgrp and exit */
-static void set_fatal_handlers_to_sigexit(void)
+static void install_fatal_sighandlers(void)
 {
-        void (*handler)(int);
-        unsigned fatal_sigs, sig;
+        unsigned mask;
 
         /* We will restore tty pgrp on these signals */
-        fatal_sigs = 0
+        mask = 0
                 + (1 << SIGILL ) * HUSH_DEBUG
                 + (1 << SIGFPE ) * HUSH_DEBUG
                 + (1 << SIGBUS ) * HUSH_DEBUG
@@ -7505,22 +7580,13 @@ static void set_fatal_handlers_to_sigexit(void)
                 /*+ (1 << SIGTERM)*/
                 /*+ (1 << SIGINT )*/
         ;
-
-        /* special_sig_mask'ed signals are, well, masked,
+        /* special_sig_mask'ed signals are set to record_pending_signo
          * no need to set handler for them.
          */
-        fatal_sigs &= ~G.special_sig_mask;
+        /*mask &= ~G.special_sig_mask; - they never overlap */
+        G_fatal_sig_mask = mask;
 
-        /* For each sig in fatal_sigs... */
-        sig = 0;
-        while ((fatal_sigs >>= 1) != 0) {
-                sig++;
-                if (!(fatal_sigs & 1))
-                        continue;
-                handler = signal(sig, sigexit);
-                if (handler == SIG_IGN) /* oops... restore back to IGN! */
-                        signal(sig, handler);
-        }
+        install_sighandlers(mask);
 }
 #endif
 
@@ -7682,10 +7748,11 @@ int hush_main(int argc, char **argv)
         }
 
         /* Shell is non-interactive at first. We need to call
-         * init_sigmasks() if we are going to execute "sh <script>",
+         * install_special_sighandlers() if we are going to execute "sh <script>",
          * "sh -c <cmds>" or login shell's /etc/profile and friends.
-         * If we later decide that we are interactive, we run init_sigmasks()
+         * If we later decide that we are interactive, we run install_special_sighandlers()
          * in order to intercept (more) signals.
+//FIXME: re-running is currently most likely broken, it's a no-op.
          */
 
         /* Parse options */
@@ -7724,7 +7791,7 @@ int hush_main(int argc, char **argv)
                                 /* -c 'builtin' [BARGV...] "" ARG0 [ARG1...] */
                                 const struct built_in_command *x;
 
-                                init_sigmasks();
+                                install_special_sighandlers();
                                 x = find_builtin(optarg);
                                 if (x) { /* paranoia */
                                         G.global_argc -= builtin_argc; /* skip [BARGV...] "" */
@@ -7741,7 +7808,7 @@ int hush_main(int argc, char **argv)
                                 G.global_argv[0] = argv[0];
                                 G.global_argc++;
                         } /* else -c 'script' ARG0 [ARG1...]: $0 is ARG0 */
-                        init_sigmasks();
+                        install_special_sighandlers();
                         parse_and_run_string(optarg);
                         goto final_return;
                 case 'i':
@@ -7773,15 +7840,15 @@ int hush_main(int argc, char **argv)
                         empty_trap_mask = bb_strtoull(optarg, &optarg, 16);
                         if (empty_trap_mask != 0) {
                                 int sig;
-                                init_sigmasks();
+                                install_special_sighandlers();
                                 G.traps = xzalloc(sizeof(G.traps[0]) * NSIG);
                                 for (sig = 1; sig < NSIG; sig++) {
+///vda: fixme: more efficient code
                                         if (empty_trap_mask & (1LL << sig)) {
                                                 G.traps[sig] = xzalloc(1); /* == xstrdup(""); */
-                                                sigaddset(&G.blocked_set, sig);
+                                                signal(sig, SIG_IGN);
                                         }
                                 }
-                                sigprocmask_set(&G.blocked_set);
                         }
 # if ENABLE_HUSH_LOOPS
                         optarg++;
@@ -7831,7 +7898,7 @@ int hush_main(int argc, char **argv)
                 input = fopen_for_read("/etc/profile");
                 if (input != NULL) {
                         close_on_exec_on(fileno(input));
-                        init_sigmasks();
+                        install_special_sighandlers();
                         parse_and_run_file(input);
                         fclose(input);
                 }
@@ -7856,7 +7923,7 @@ int hush_main(int argc, char **argv)
                 G.global_argc = argc - optind;
                 input = xfopen_for_read(argv[optind]);
                 close_on_exec_on(fileno(input));
-                init_sigmasks();
+                install_special_sighandlers();
                 parse_and_run_file(input);
 #if ENABLE_FEATURE_CLEAN_UP
                 fclose(input);
@@ -7865,7 +7932,7 @@ int hush_main(int argc, char **argv)
         }
 
         /* Up to here, shell was non-interactive. Now it may become one.
-         * NB: don't forget to (re)run init_sigmasks() as needed.
+         * NB: don't forget to (re)run install_special_sighandlers() as needed.
          */
 
         /* A shell is interactive if the '-i' flag was given,
@@ -7918,11 +7985,11 @@ int hush_main(int argc, char **argv)
                 }
 
                 /* Block some signals */
-                init_sigmasks();
+                install_special_sighandlers();
 
                 if (G_saved_tty_pgrp) {
                         /* Set other signals to restore saved_tty_pgrp */
-                        set_fatal_handlers_to_sigexit();
+                        install_fatal_sighandlers();
                         /* Put ourselves in our own process group
                          * (bash, too, does this only if ctty is available) */
                         bb_setpgrp(); /* is the same as setpgid(our_pid, our_pid); */
@@ -7933,7 +8000,7 @@ int hush_main(int argc, char **argv)
                  * (we reset die_sleep = 0 whereever we [v]fork) */
                 enable_restore_tty_pgrp_on_exit(); /* sets die_sleep = -1 */
         } else {
-                init_sigmasks();
+                install_special_sighandlers();
         }
 #elif ENABLE_HUSH_INTERACTIVE
         /* No job control compiled in, only prompt/line editing */
@@ -7950,10 +8017,10 @@ int hush_main(int argc, char **argv)
         if (G_interactive_fd) {
                 close_on_exec_on(G_interactive_fd);
         }
-        init_sigmasks();
+        install_special_sighandlers();
 #else
         /* We have interactiveness code disabled */
-        init_sigmasks();
+        install_special_sighandlers();
 #endif
         /* bash:
          * if interactive but not a login shell, sources ~/.bashrc
@@ -8087,7 +8154,7 @@ static int FAST_FUNC builtin_exec(char **argv)
                 tcsetpgrp(G_interactive_fd, G_saved_tty_pgrp);
 
         /* TODO: if exec fails, bash does NOT exit! We do.
-         * We'll need to undo sigprocmask (it's inside execvp_or_die)
+         * We'll need to undo trap cleanup (it's inside execvp_or_die)
          * and tcsetpgrp, and this is inherently racy.
          */
         execvp_or_die(argv);
@@ -8284,6 +8351,8 @@ static int FAST_FUNC builtin_trap(char **argv)
  process_sig_list:
                 ret = EXIT_SUCCESS;
                 while (*argv) {
+                        sighandler_t handler;
+
                         sig = get_signum(*argv++);
                         if (sig < 0 || sig >= NSIG) {
                                 ret = EXIT_FAILURE;
@@ -8302,18 +8371,13 @@ static int FAST_FUNC builtin_trap(char **argv)
                         if (sig == 0)
                                 continue;
 
-                        if (new_cmd) {
-                                sigaddset(&G.blocked_set, sig);
-                        } else {
-                                /* There was a trap handler, we are removing it
-                                 * (if sig has non-DFL handling,
-                                 * we don't need to do anything) */
-                                if (sig < sizeof(G.special_sig_mask)*8 && (G.special_sig_mask & (1 << sig)))
-                                        continue;
-                                sigdelset(&G.blocked_set, sig);
-                        }
+                        if (new_cmd)
+                                handler = (new_cmd[0] ? record_pending_signo : SIG_IGN);
+                        else
+                                /* We are removing trap handler */
+                                handler = pick_sighandler(sig);
+                        signal(sig, handler);
                 }
-                sigprocmask_set(&G.blocked_set);
                 return ret;
         }
 
@@ -8535,11 +8599,6 @@ static int FAST_FUNC builtin_pwd(char **argv UNUSED_PARAM)
  * if it has non-empty trap:
  * - executes trap and returns to read;
  */
-/* helper */
-static void record_signal(int sig)
-{
-        sigaddset(&G.detected_set, sig);
-}
 static int FAST_FUNC builtin_read(char **argv)
 {
         const char *r;
@@ -8549,7 +8608,6 @@ static int FAST_FUNC builtin_read(char **argv)
         char *opt_u = NULL;
         const char *ifs;
         int read_flags;
-        sigset_t saved_blkd_set;
 
         /* "!": do not abort on errors.
          * Option string must start with "sr" to match BUILTIN_READ_xxx
@@ -8561,41 +8619,6 @@ static int FAST_FUNC builtin_read(char **argv)
         ifs = get_local_var_value("IFS"); /* can be NULL */
 
  again:
-        /* We need to temporarily unblock and record signals around read */
-
-        saved_blkd_set = G.blocked_set;
-        {
-                unsigned sig;
-                struct sigaction sa, old_sa;
-
-                memset(&sa, 0, sizeof(sa));
-                sigfillset(&sa.sa_mask);
-                sa.sa_flags = SA_RESTART;
-                sa.sa_handler = record_signal;
-
-                sig = 0;
-                do {
-                        sig++;
-                        if (sigismember(&G.blocked_set, sig)) {
-                                char *sig_trap = (G.traps && G.traps[sig]) ? G.traps[sig] : NULL;
-                                /* If has a nonempty trap... */
-                                if ((sig_trap && sig_trap[0])
-                                /* ...or has no trap and is SIGINT or SIGHUP */
-                                 || (!sig_trap && (sig == SIGINT || sig == SIGHUP))
-                                ) {
-                                        sigaction(sig, &sa, &old_sa);
-                                        if (old_sa.sa_handler == SIG_IGN) /* oops... restore back to IGN! */
-                                                sigaction_set(sig, &old_sa);
-                                        else
-                                                sigdelset(&G.blocked_set, sig);
-                                }
-                        }
-                } while (sig < NSIG-1);
-        }
-
-        if (memcmp(&saved_blkd_set, &G.blocked_set, sizeof(saved_blkd_set)) != 0)
-                sigprocmask_set(&G.blocked_set);
-
         r = shell_builtin_read(set_local_var_from_halves,
                 argv,
                 ifs,
@@ -8606,13 +8629,8 @@ static int FAST_FUNC builtin_read(char **argv)
                 opt_u
         );
 
-        if (memcmp(&saved_blkd_set, &G.blocked_set, sizeof(saved_blkd_set)) != 0) {
-                G.blocked_set = saved_blkd_set;
-                sigprocmask_set(&G.blocked_set);
-        }
-
         if ((uintptr_t)r == 1 && errno == EINTR) {
-                unsigned sig = check_and_run_traps(0);
+                unsigned sig = check_and_run_traps();
                 if (sig && sig != SIGINT)
                         goto again;
         }
@@ -8849,7 +8867,7 @@ static int FAST_FUNC builtin_unset(char **argv)
 static int FAST_FUNC builtin_wait(char **argv)
 {
         int ret = EXIT_SUCCESS;
-        int status, sig;
+        int status;
 
         argv = skip_dash_dash(argv);
         if (argv[0] == NULL) {
@@ -8869,25 +8887,53 @@ static int FAST_FUNC builtin_wait(char **argv)
                  * ^C <-- after ~4 sec from keyboard
                  * $
                  */
-                sigaddset(&G.blocked_set, SIGCHLD);
-                sigprocmask_set(&G.blocked_set);
                 while (1) {
-                        checkjobs(NULL);
-                        if (errno == ECHILD)
+                        int sig;
+                        sigset_t oldset, allsigs;
+
+                        /* waitpid is not interruptible by SA_RESTARTed
+                         * signals which we use. Thus, this ugly dance:
+                         */
+
+                        /* Make sure possible SIGCHLD is stored in kernel's
+                         * pending signal mask before we call waitpid.
+                         * Or else we may race with SIGCHLD, lose it,
+                         * and get stuck in sigwaitinfo...
+                         */
+                        sigfillset(&allsigs);
+                        sigprocmask(SIG_SETMASK, &allsigs, &oldset);
+
+                        if (!sigisemptyset(&G.pending_set)) {
+                                /* Crap! we raced with some signal! */
+                        //      sig = 0;
+                                goto restore;
+                        }
+
+                        checkjobs(NULL); /* waitpid(WNOHANG) inside */
+                        if (errno == ECHILD) {
+                                sigprocmask(SIG_SETMASK, &oldset, NULL);
+                                break;
+                        }
+
+                        /* Wait for SIGCHLD or any other signal */
+                        //sig = sigwaitinfo(&allsigs, NULL);
+                        /* It is vitally important for sigsuspend that SIGCHLD has non-DFL handler! */
+                        /* Note: sigsuspend invokes signal handler */
+                        sigsuspend(&oldset);
+ restore:
+                        sigprocmask(SIG_SETMASK, &oldset, NULL);
+
+                        /* So, did we get a signal? */
+                        //if (sig > 0)
+                        //      raise(sig); /* run handler */
+                        sig = check_and_run_traps();
+                        if (sig /*&& sig != SIGCHLD - always true */) {
+                                /* see note 2 */
+                                ret = 128 + sig;
                                 break;
-                        /* Wait for SIGCHLD or any other signal of interest */
-                        /* sigtimedwait with infinite timeout: */
-                        sig = sigwaitinfo(&G.blocked_set, NULL);
-                        if (sig > 0) {
-                                sig = check_and_run_traps(sig);
-                                if (sig && sig != SIGCHLD) { /* see note 2 */
-                                        ret = 128 + sig;
-                                        break;
-                                }
                         }
+                        /* SIGCHLD, or no signal, or ignored one, such as SIGQUIT. Repeat */
                 }
-                sigdelset(&G.blocked_set, SIGCHLD);
-                sigprocmask_set(&G.blocked_set);
                 return ret;
         }