sheel: improve comments on signal handling

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

2 files changed, 23 insertions, 11 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 8c9f4adc6..ca9926b54 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -3536,9 +3536,12 @@ setsignal(int signo)
 #endif
                 }
         }
-//TODO: if !rootshell, we reset SIGQUIT to DFL,
-//whereas we have to restore it to what shell got on entry
-//from the parent. See comment above
+        /* if !rootshell, we reset SIGQUIT to DFL,
+         * whereas we have to restore it to what shell got on entry.
+         * This is handled by the fact that if signal was IGNored on entry,
+         * then cur_act is S_HARD_IGN and we never change its sigaction
+         * (see code below).
+         */
 
         if (signo == SIGCHLD)
                 new_act = S_CATCH;
@@ -3566,6 +3569,8 @@ setsignal(int signo)
         if (cur_act == S_HARD_IGN || cur_act == new_act)
                 return;
 
+        *t = new_act;
+
         act.sa_handler = SIG_DFL;
         switch (new_act) {
         case S_CATCH:
@@ -3575,16 +3580,13 @@ setsignal(int signo)
                 act.sa_handler = SIG_IGN;
                 break;
         }
-
         /* flags and mask matter only if !DFL and !IGN, but we do it
          * for all cases for more deterministic behavior:
          */
-        act.sa_flags = 0;
+        act.sa_flags = 0; //TODO: why not SA_RESTART?
         sigfillset(&act.sa_mask);
 
         sigaction_set(signo, &act);
-
-        *t = new_act;
 }
 
 /* mode flags for set_curjob */
@@ -13429,7 +13431,9 @@ readcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
         INT_ON;
 
         if ((uintptr_t)r == 1 && errno == EINTR) {
-                /* to get SIGCHLD: sleep 1 & read x; echo $x */
+                /* To get SIGCHLD: sleep 1 & read x; echo $x
+                 * Correct behavior is to not exit "read"
+                 */
                 if (pending_sig == 0)
                         goto again;
         }
@@ -13544,13 +13548,14 @@ exitshell(void)
         /* NOTREACHED */
 }
 
-static void
+/* Don't inline: conserve stack of caller from having our locals too */
+static NOINLINE void
 init(void)
 {
         /* we will never free this */
         basepf.next_to_pgetc = basepf.buf = ckmalloc(IBUFSIZ);
 
-        sigmode[SIGCHLD - 1] = S_DFL;
+        sigmode[SIGCHLD - 1] = S_DFL; /* ensure we install handler even if it is SIG_IGNed */
         setsignal(SIGCHLD);
 
         /* bash re-enables SIGHUP which is SIG_IGNed on entry.
@@ -13561,7 +13566,6 @@ init(void)
         {
                 char **envp;
                 const char *p;
-                struct stat st1, st2;
 
                 initvar();
                 for (envp = environ; envp && *envp; envp++) {
@@ -13587,6 +13591,7 @@ init(void)
 #endif
                 p = lookupvar("PWD");
                 if (p) {
+                        struct stat st1, st2;
                         if (p[0] != '/' || stat(p, &st1) || stat(".", &st2)
                          || st1.st_dev != st2.st_dev || st1.st_ino != st2.st_ino
                         ) {
diff --git a/shell/hush.c b/shell/hush.c
index b04f793f1..bb80f422c 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -1979,6 +1979,9 @@ static int check_and_run_traps(void)
                         break;
 #if ENABLE_HUSH_JOB
                 case SIGHUP: {
+//TODO: why are we doing this? ash and dash don't do this,
+//they have no handler for SIGHUP at all,
+//they rely on kernel to send SIGHUP+SIGCONT to orphaned process groups
                         struct pipe *job;
                         debug_printf_exec("%s: sig:%d default SIGHUP handler\n", __func__, sig);
                         /* bash is observed to signal whole process groups,
@@ -8646,6 +8649,10 @@ static void install_sighandlers(unsigned mask)
                  */
                 if (sig == SIGCHLD)
                         continue;
+                /* bash re-enables SIGHUP which is SIG_IGNed on entry.
+                 * Try: "trap '' HUP; bash; echo RET" and type "kill -HUP $$"
+                 */
+                //if (sig == SIGHUP) continue; - TODO?
                 if (old_handler == SIG_IGN) {
                         /* oops... restore back to IGN, and record this fact */
                         install_sighandler(sig, old_handler);