win32: use built-in applets for non-existent binaries with Unix-style paths

Shell scripts moved from Unix may contain hard-coded paths to
binaries such as /bin/sh.  A recent commit made it possible to
execute such binaries reliably, but that does require them to be
installed.  As an alternative solution:  if a binary with a
standard Unix path prefix can't be found but is available as a
built-in applet, run the applet.

Add the function unix_path() to detect paths starting with /bin,
/usr/bin, /sbin or /usr/sbin.

Use this function in:

- the 'which' applet
- shellexec(), describe_command() and find_command() in ash
- mingw_spawn_1()

See GitHub issue #195.

1 files changed, 46 insertions, 9 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 0a638b1df..2267e841f 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -8754,6 +8754,9 @@ static void shellexec(char *prog, char **argv, const char *path, int idx)
 #endif
         ) {
 #if ENABLE_PLATFORM_MINGW32
+# if ENABLE_FEATURE_SH_STANDALONE
+                char *oldprog = prog;
+# endif
                 prog = auto_add_system_drive(prog);
 #endif
                 tryexec(IF_FEATURE_SH_STANDALONE(applet_no,) prog, argv, envp);
@@ -8764,6 +8767,14 @@ static void shellexec(char *prog, char **argv, const char *path, int idx)
                          */
                         goto try_PATH;
                 }
+#if ENABLE_PLATFORM_MINGW32 && ENABLE_FEATURE_SH_STANDALONE
+                if (oldprog != prog && unix_path(oldprog)) {
+                        if ((applet_no = find_applet_by_name(bb_basename(oldprog))) >= 0)
+                                tryexec(applet_no, bb_basename(oldprog), argv, envp);
+                        else
+                                errno = ENOENT;
+                }
+#endif
                 e = errno;
         } else {
  try_PATH:
@@ -9191,6 +9202,12 @@ describe_command(char *command, const char *path, int describe_command_verbose)
         case CMDNORMAL: {
                 int j = entry.u.index;
                 char *p;
+#if ENABLE_PLATFORM_MINGW32 && ENABLE_FEATURE_SH_STANDALONE
+                if (j == INT_MIN) {
+                        p = (char *)bb_basename(command);
+                        goto describe;
+                }
+#endif
                 if (j < 0) {
 #if ENABLE_PLATFORM_MINGW32
                         /* can't use auto_add_system_drive, need space for extension */
@@ -9211,6 +9228,7 @@ describe_command(char *command, const char *path, int describe_command_verbose)
 #if ENABLE_PLATFORM_MINGW32
                 add_win32_extension(p);
                 bs_to_slash(p);
+ IF_FEATURE_SH_STANDALONE(describe:)
 #endif
                 if (describe_command_verbose) {
                         out1fmt(" is %s", p);
@@ -14268,24 +14286,16 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
         struct builtincmd *bcmd;
         int len;
 
+#if !ENABLE_PLATFORM_MINGW32
         /* If name contains a slash, don't use PATH or hash table */
-#if ENABLE_PLATFORM_MINGW32
-        if (has_path(name)) {
-                name = auto_add_system_drive(name);
-#else
         if (strchr(name, '/') != NULL) {
-#endif
                 entry->u.index = -1;
                 if (act & DO_ABS) {
-#if ENABLE_PLATFORM_MINGW32
-                        if (auto_win32_extension(name) == NULL && stat(name, &statb) < 0) {
-#else
                         while (stat(name, &statb) < 0) {
 #ifdef SYSV
                                 if (errno == EINTR)
                                         continue;
 #endif
-#endif
                                 entry->cmdtype = CMDUNKNOWN;
                                 return;
                         }
@@ -14293,6 +14303,33 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
                 entry->cmdtype = CMDNORMAL;
                 return;
         }
+#else /* ENABLE_PLATFORM_MINGW32 */
+        /* If name contains a slash or drive prefix, don't use PATH or hash table */
+        if (has_path(name)) {
+# if ENABLE_FEATURE_SH_STANDALONE
+        char *oldname = name;
+# endif
+                name = auto_add_system_drive(name);
+                entry->u.index = -1;
+                if (act & DO_ABS) {
+                        if (auto_win32_extension(name) == NULL && stat(name, &statb) < 0) {
+# if ENABLE_FEATURE_SH_STANDALONE
+                                int applet_no;
+                                if (unix_path(oldname) &&
+                                                (applet_no = find_applet_by_name(bb_basename(oldname))) >= 0) {
+                                        entry->cmdtype = CMDNORMAL;
+                                        entry->u.index = INT_MIN;
+                                        return;
+                                }
+# endif
+                                entry->cmdtype = CMDUNKNOWN;
+                                return;
+                        }
+                }
+                entry->cmdtype = CMDNORMAL;
+                return;
+        }
+#endif /* ENABLE_PLATFORM_MINGW32 */
 
 /* #if ENABLE_FEATURE_SH_STANDALONE... moved after builtin check */