ash: optimise running of scripts

The BusyBox shell detects certain cases where forking a command is
unnecessary (last command in a script or subshell, for example) and
calls execve(2) instead.  This doesn't help in the Windows port
because execve(2) is implemented by creating a process.

There is one case where it is possible to apply this optimisation:
if the command is a script and the script interpreter is an applet.

- Have evalcommand() pass a flag to indicate this situation to
  shellexec().  Also, allocate two spare elements before the start
  of the argv array.

- If the flag is TRUE shellexec() passes the shell's PATH variable
  down to tryexec() so it can perform a test for applet override.

- If tryexec() finds that all the necessary conditions apply it
  can run a script by directly invoking the interpreter's main().

Adds 192-224 bytes.

1 files changed, 8 insertions, 0 deletions

diff --git a/include/mingw.h b/include/mingw.h
index adb810ec5..ed7884e39 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -566,6 +566,14 @@ int utimes(const char *file_name, const struct timeval times[2]);
 #define is_unc_path(x) (strlen(x) > 4 && is_dir_sep(x[0]) && \
                                                         is_dir_sep(x[1]) && !is_dir_sep(x[2]))
 
+typedef struct {
+        char *path;
+        char *name;
+        char *opts;
+        char buf[100];
+} interp_t;
+
+int FAST_FUNC parse_interpreter(const char *cmd, interp_t *interp);
 char ** FAST_FUNC grow_argv(char **argv, int n);
 pid_t FAST_FUNC mingw_spawn(char **argv);
 intptr_t FAST_FUNC mingw_spawn_detach(char **argv);