ash: better handling of EXIT trap in `trap` hack

function                                             old     new   delta
forkchild                                              -     602    +602
trapcmd                                              255     347     +92
ash_main                                            1362    1375     +13
evalvar                                             1371    1373      +2
popstring                                            140     134      -6
forkshell                                            835     248    -587
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 3/2 up/down: 709/-593)          Total: 116 bytes

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

5 files changed, 38 insertions, 9 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 47f968b54..b30dc7728 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -193,6 +193,7 @@ struct globals_misc {
         /* indicates specified signal received */
         uint8_t gotsig[NSIG - 1]; /* offset by 1: "signal" 0 is meaningless */
         char *trap[NSIG];
+        char **trap_ptr;        /* used only by "trap hack" */
 
         /* Rarely referenced stuff */
 #if ENABLE_ASH_RANDOM_SUPPORT
@@ -222,6 +223,7 @@ extern struct globals_misc *const ash_ptr_to_globals_misc;
 #define sigmode     (G_misc.sigmode    )
 #define gotsig      (G_misc.gotsig     )
 #define trap        (G_misc.trap       )
+#define trap_ptr    (G_misc.trap_ptr   )
 #define random_galois_LFSR (G_misc.random_galois_LFSR)
 #define random_LCG         (G_misc.random_LCG        )
 #define backgndpid  (G_misc.backgndpid )
@@ -231,6 +233,7 @@ extern struct globals_misc *const ash_ptr_to_globals_misc;
         barrier(); \
         curdir = nullstr; \
         physdir = nullstr; \
+        trap_ptr = trap; \
 } while (0)
 
 
@@ -4539,7 +4542,7 @@ static void closescript(void);
 #if !JOBS
 # define forkchild(jp, n, mode) forkchild(jp, mode)
 #endif
-static void
+static NOINLINE void
 forkchild(struct job *jp, union node *n, int mode)
 {
         int oldlvl;
@@ -4596,8 +4599,10 @@ forkchild(struct job *jp, union node *n, int mode)
                  *
                  * Our solution: ONLY bare $(trap) or `trap` is special.
                  */
-                free(trap[0]); /* Prevent EXIT trap from firing in `trap` */
-                trap[0] = NULL;
+                /* This is needed to prevent EXIT trap firing and such
+                 * (trap_ptr will be freed in trapcmd()) */
+                trap_ptr = memcpy(xmalloc(sizeof(trap)), trap, sizeof(trap));
+                memset(trap, 0, sizeof(trap));
         } else {
                 clear_traps();
         }
@@ -12260,15 +12265,23 @@ trapcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
         ap = argptr;
         if (!*ap) {
                 for (signo = 0; signo < NSIG; signo++) {
-                        if (trap[signo] != NULL) {
+                        char *tr = trap_ptr[signo];
+                        if (tr) {
                                 out1fmt("trap -- %s %s%s\n",
-                                                single_quote(trap[signo]),
+                                                single_quote(tr),
                                                 (signo == 0 ? "" : "SIG"),
                                                 get_signame(signo));
+                                if (trap_ptr != trap)
+                                        free(tr);
                         }
                 }
+                if (trap_ptr != trap) {
+                        free(trap_ptr);
+                        trap_ptr = trap;
+                }
                 return 0;
         }
+
         action = NULL;
         if (ap[1])
                 action = *ap++;
diff --git a/shell/ash_test/ash-signals/savetrap.right b/shell/ash_test/ash-signals/savetrap.right
index 2d33427aa..9cfd7a56c 100644
--- a/shell/ash_test/ash-signals/savetrap.right
+++ b/shell/ash_test/ash-signals/savetrap.right
@@ -1,3 +1,8 @@
+trap -- 'echo Exiting' EXIT
 trap -- 'echo WINCH!' SIGWINCH
+trap -- 'echo Exiting' EXIT
+trap -- 'echo WINCH!' SIGWINCH
+trap -- 'echo Exiting' EXIT
 trap -- 'echo WINCH!' SIGWINCH
 Done
+Exiting
diff --git a/shell/ash_test/ash-signals/savetrap.tests b/shell/ash_test/ash-signals/savetrap.tests
index 6492e86a2..c2b312fb8 100755
--- a/shell/ash_test/ash-signals/savetrap.tests
+++ b/shell/ash_test/ash-signals/savetrap.tests
@@ -1,6 +1,9 @@
+trap 'echo Exiting' EXIT
 trap 'echo WINCH!' SIGWINCH
 v=` trap   `
-echo $v
+echo "$v"
+v=$(    trap )
+echo "$v"
 v=`trap`
-echo $v
+echo "$v"
 echo Done
diff --git a/shell/hush_test/hush-trap/savetrap.right b/shell/hush_test/hush-trap/savetrap.right
index 2d33427aa..9cfd7a56c 100644
--- a/shell/hush_test/hush-trap/savetrap.right
+++ b/shell/hush_test/hush-trap/savetrap.right
@@ -1,3 +1,8 @@
+trap -- 'echo Exiting' EXIT
 trap -- 'echo WINCH!' SIGWINCH
+trap -- 'echo Exiting' EXIT
+trap -- 'echo WINCH!' SIGWINCH
+trap -- 'echo Exiting' EXIT
 trap -- 'echo WINCH!' SIGWINCH
 Done
+Exiting
diff --git a/shell/hush_test/hush-trap/savetrap.tests b/shell/hush_test/hush-trap/savetrap.tests
index 6492e86a2..c2b312fb8 100755
--- a/shell/hush_test/hush-trap/savetrap.tests
+++ b/shell/hush_test/hush-trap/savetrap.tests
@@ -1,6 +1,9 @@
+trap 'echo Exiting' EXIT
 trap 'echo WINCH!' SIGWINCH
 v=` trap   `
-echo $v
+echo "$v"
+v=$(    trap )
+echo "$v"
 v=`trap`
-echo $v
+echo "$v"
 echo Done