ash: optimise running of scripts (2)

Commit 4b7b4a960 (ash: optimise running of scripts) avoided creation
of a process when running a script.  There's another case where we
can do the same:  if the script is being run from a FS_SHELLEXEC
shell.

- Check the necessary conditions for this to happen.

- Allocate two extra slots in the argv array for FS_SHELLEXEC.

- Set the index of the script file in the argv array.  Without this
  the test 'pidof this' failed because the command name hadn't been
  correctly set.

Adds 80-96 bytes.

3 files changed, 26 insertions, 8 deletions

diff --git a/include/mingw.h b/include/mingw.h
index ed7884e39..65940b40b 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -667,3 +667,4 @@ enum {
         ADMIN_ENABLED = 2
 };
 int elevation_state(void);
+void set_interp(int i) FAST_FUNC;
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 97dfb3df8..1ff7fe6c8 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -394,6 +394,13 @@ bool re_execed;
 static int interp = 0;
 char bb_comm[COMM_LEN];
 char bb_command_line[128];
+
+# if ENABLE_FEATURE_SH_STANDALONE
+void FAST_FUNC set_interp(int i)
+{
+        interp = i;
+}
+# endif
 #endif
 
 
diff --git a/shell/ash.c b/shell/ash.c
index 2e4181b3f..d9a7bee83 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -9099,6 +9099,7 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) const char *cmd, char **argv, c
 #endif
 {
 #if ENABLE_PLATFORM_MINGW32 && ENABLE_FEATURE_SH_STANDALONE
+        struct forkshell *fs = (struct forkshell *)sticky_mem_start;
         interp_t interp;
 #endif
 #if ENABLE_FEATURE_SH_STANDALONE
@@ -9106,7 +9107,6 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) const char *cmd, char **argv, c
 # if ENABLE_PLATFORM_MINGW32
                 /* Treat all applets as NOEXEC, including the shell itself if
                  * this is a FS_SHELLEXEC shell. */
-                struct forkshell *fs = (struct forkshell *)sticky_mem_start;
                 if (applet_main[applet_no] != ash_main ||
                                 (fs && fs->fpid == FS_SHELLEXEC)) {
  run_noexec:
@@ -9152,21 +9152,28 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) const char *cmd, char **argv, c
         add_win32_extension((char *)cmd);
 
 # if ENABLE_FEATURE_SH_STANDALONE
-        /* If nfpath is non-NULL, evalcommand() has determined this
-         * command doesn't need a fork().  If the command is a script
-         * with an interpreter which is an applet we can run it as if
-         * it were a noexec applet. */
+        /* If nfpath is non-NULL evalcommand() has determined this
+         * command doesn't need a fork().  Even it's NULL we can
+         * possibly avoid a fork if this is a FS_SHELLEXEC shell. */
+        if (nfpath == NULL && (fs && fs->fpid == FS_SHELLEXEC))
+                nfpath = pathval();
+
+        /* If nfpath is non-NULL and the command is a script with an
+         * interpreter which is an applet, we can run it as if it
+         * were a noexec applet. */
         if (nfpath && parse_interpreter(cmd, &interp)) {
                 applet_no = find_applet_by_name_for_sh(interp.name, nfpath);
                 if (applet_no >= 0) {
                         argv[0] = (char *)cmd;
-                        /* evalcommand() has added two elements before argv */
+                        /* evalcommand()/spawn_forkshell() add two elements before argv */
                         if (interp.opts) {
                                 argv--;
                                 argv[0] = (char *)interp.opts;
                         }
                         argv--;
                         cmd = argv[0] = (char *)interp.name;
+                        /* Identify the index of the script file in argv */
+                        set_interp(1 + (interp.opts != NULL));
                         goto run_noexec;
                 }
         }
@@ -16842,7 +16849,8 @@ argv_size(struct datasize ds, char **p)
                         ds.funcstringsize += align_len(*p);
                         p++;
                 }
-                ds.funcblocksize += sizeof(char *);
+                // Allow two extra elements for tryexec().
+                ds.funcblocksize += 3 * sizeof(char *);
         }
         return ds;
 }
@@ -16856,6 +16864,8 @@ argv_copy(char **p)
 #endif
 
         if (p) {
+                // Allow two extra elements for tryexec().
+                funcblock = (char *) funcblock + 2 * sizeof(char *);
                 while (*p) {
                         new = funcblock;
                         funcblock = (char *) funcblock + sizeof(char *);
@@ -16866,7 +16876,7 @@ argv_copy(char **p)
                 new = funcblock;
                 funcblock = (char *) funcblock + sizeof(char *);
                 *new = NULL;
-                return start;
+                return start + 2;
         }
         return NULL;
 }