win32: handle Unix-style absolute paths for executables

As noted in commit 548ec7045 (win32: interpret absolute paths as
relative to %SYSTEMDRIVE%) a path starting with a '/' in the Unix
world is treated as relative to the current drive by Windows.
To avoid ambiguity that commit considered certain such paths to
be relative to %SYSTEMDRIVE%.  Extend this to paths representing
executables.

Add the functions need_system_drive() and auto_add_system_drive()
to detect the need for a system drive prefix and to add it if
necessary.  Use these functions in:

- the 'which' applet
- the find_executable() function
- tab-completion code
- PATH look-up, shellexec(), describe_command() and find_command() in ash
- parse_interpreter() and mingw_spawn_1()

With these changes executable paths starting with a slash are
handled consistently, whatever the current drive.

7 files changed, 68 insertions, 4 deletions

diff --git a/debianutils/which.c b/debianutils/which.c
index 1f8c1a538..c8e99acda 100644
--- a/debianutils/which.c
+++ b/debianutils/which.c
@@ -71,6 +71,7 @@ int which_main(int argc UNUSED_PARAM, char **argv)
                 if (strchr(*argv, '/')) {
 #else
                 if (has_path(*argv)) {
+                        *argv = auto_add_system_drive(*argv);
                         if ((p=auto_win32_extension(*argv)) != NULL) {
                                 missing = 0;
                                 puts(bs_to_slash(p));
diff --git a/include/mingw.h b/include/mingw.h
index 91e4dc1a5..434f3a474 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -547,6 +547,8 @@ void hide_console(void);
 int unc_root_len(const char *dir);
 int root_len(const char *path);
 const char *get_system_drive(void);
+const char *need_system_drive(const char *path);
+char *auto_add_system_drive(const char *path);
 int chdir_system_drive(void);
 char *xabsolute_path(char *path);
 char *get_drive_cwd(const char *path, char *buffer, int size);
diff --git a/libbb/executable.c b/libbb/executable.c
index 87a40eeda..0a0769ef3 100644
--- a/libbb/executable.c
+++ b/libbb/executable.c
@@ -49,6 +49,9 @@ char* FAST_FUNC find_executable(const char *filename, char **PATHp)
 
                 n = strchr(p, PATH_SEP);
                 if (n) *n = '\0';
+#if ENABLE_PLATFORM_MINGW32
+                p = auto_add_system_drive(p);
+#endif
                 p = concat_path_file(
                         p[0] ? p : ".", /* handle "::" case */
                         filename
diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index a36a1647d..f6577e372 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -913,8 +913,12 @@ static NOINLINE unsigned complete_cmd_dir_file(const char *command, int type)
                 struct dirent *next;
                 struct stat st;
                 char *found;
-
+#if ENABLE_PLATFORM_MINGW32
+                char *lpath = auto_add_system_drive(paths[i]);
+                dir = opendir(lpath);
+#else
                 dir = opendir(paths[i]);
+#endif
                 if (!dir)
                         continue; /* don't print an error */
 
@@ -929,7 +933,11 @@ static NOINLINE unsigned complete_cmd_dir_file(const char *command, int type)
                         if (!is_prefixed_with(name_found, pfind))
                                 continue; /* no */
 
+#if ENABLE_PLATFORM_MINGW32
+                        found = concat_path_file(lpath, name_found);
+#else
                         found = concat_path_file(paths[i], name_found);
+#endif
                         /* NB: stat() first so that we see is it a directory;
                          * but if that fails, use lstat() so that
                          * we still match dangling links */
diff --git a/shell/ash.c b/shell/ash.c
index 7a2d0ab68..0a638b1df 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -2828,6 +2828,10 @@ padvance_magic(const char **path, const char *name, int magic)
         const char *start;
         size_t qlen;
         size_t len;
+#if ENABLE_PLATFORM_MINGW32
+        size_t sdlen = 0;
+        const char *sd;
+#endif
 
         if (*path == NULL)
                 return -1;
@@ -2859,11 +2863,20 @@ padvance_magic(const char **path, const char *name, int magic)
         *path = *p == PATH_SEP ? p + 1 : NULL;
 
         /* "2" is for '/' and '\0' */
-        /* reserve space for suffix on WIN32 */
-        qlen = len + strlen(name) + 2 IF_PLATFORM_MINGW32(+ 4);
+        qlen = len + strlen(name) + 2;
+#if ENABLE_PLATFORM_MINGW32
+        /* reserve space for system drive prefix and extension */
+        sd = need_system_drive(start);
+        if (sd != NULL)
+                sdlen = strlen(sd);
+        qlen += 4 + sdlen;
+#endif
         q = growstackto(qlen);
 
         if (len) {
+#if ENABLE_PLATFORM_MINGW32
+                q = mempcpy(q, sd, sdlen);
+#endif
                 q = mempcpy(q, start, len);
 #if ENABLE_PLATFORM_MINGW32
                 if (q[-1] != '/' && q[-1] != '\\')
@@ -8740,6 +8753,9 @@ static void shellexec(char *prog, char **argv, const char *path, int idx)
          || (applet_no = find_applet_by_name(prog)) >= 0
 #endif
         ) {
+#if ENABLE_PLATFORM_MINGW32
+                prog = auto_add_system_drive(prog);
+#endif
                 tryexec(IF_FEATURE_SH_STANDALONE(applet_no,) prog, argv, envp);
                 if (applet_no >= 0) {
                         /* We tried execing ourself, but it didn't work.
@@ -9176,7 +9192,16 @@ describe_command(char *command, const char *path, int describe_command_verbose)
                 int j = entry.u.index;
                 char *p;
                 if (j < 0) {
+#if ENABLE_PLATFORM_MINGW32
+                        /* can't use auto_add_system_drive, need space for extension */
+                        const char *sd = need_system_drive(command);
+                        size_t len = strlen(command) + 5 + (sd ? strlen(sd) : 0);
+
+                        p = auto_string(xmalloc(len));
+                        sprintf(p, "%s%s", sd ? sd : "", command);
+#else
                         p = command;
+#endif
                 } else {
                         do {
                                 padvance(&path, command);
@@ -14246,6 +14271,7 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
         /* 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
diff --git a/win32/mingw.c b/win32/mingw.c
index 8501ecdd4..e63ffa0ac 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1698,6 +1698,21 @@ const char *get_system_drive(void)
         return drive;
 }
 
+/* Return pointer to system drive if path is of form '/file', else NULL */
+const char *need_system_drive(const char *path)
+{
+        if (root_len(path) == 0 && (path[0] == '/' || path[0] == '\\'))
+                return get_system_drive();
+        return NULL;
+}
+
+/* Add a system drive prefix to 'path' if necessary, else return 'path' */
+char *auto_add_system_drive(const char *path)
+{
+        const char *sd = need_system_drive(path);
+        return sd ? auto_string(concat_path_file(sd, path)) : (char *)path;
+}
+
 int chdir_system_drive(void)
 {
         const char *sd = get_system_drive();
diff --git a/win32/process.c b/win32/process.c
index 1118eb18a..cd164e0ed 100644
--- a/win32/process.c
+++ b/win32/process.c
@@ -63,6 +63,7 @@ static int
 parse_interpreter(const char *cmd, interp_t *interp)
 {
         char *path, *t;
+        const char *sd;
         int n;
 
         while (TRUE) {
@@ -88,6 +89,12 @@ parse_interpreter(const char *cmd, interp_t *interp)
                 if (*t == '\0')
                         break;
 
+                sd = need_system_drive(path);
+                if (sd && strlen(sd) == 2) {
+                        path -= 2;
+                        memcpy(path, sd, 2);
+                }
+
                 interp->path = path;
                 interp->name = t;
                 interp->opts = strtok(NULL, "\r\n");
@@ -342,6 +349,7 @@ static intptr_t
 mingw_spawn_1(int mode, const char *cmd, char *const *argv, char *const *envp)
 {
         char *prog;
+        const char *path;
 
 #if ENABLE_FEATURE_PREFER_APPLETS || ENABLE_FEATURE_SH_STANDALONE
         if (find_applet_by_name(cmd) >= 0)
@@ -349,7 +357,8 @@ mingw_spawn_1(int mode, const char *cmd, char *const *argv, char *const *envp)
         else
 #endif
         if (has_path(cmd)) {
-                const char *path = auto_win32_extension(cmd);
+                cmd = auto_add_system_drive(cmd);
+                path = auto_win32_extension(cmd);
                 return mingw_spawn_interpreter(mode, path ? path : cmd, argv, envp, 0);
         }
         else if ((prog=find_first_executable(cmd)) != NULL) {