Avoid repeating original argv[0]

resolves #6
binfmt-dispatcher gets typically registered to binfmt-misc with flags `POCF`.
- `P` will preserve the original argv[0] used
- `O` will give the resolved binary (e.g. after symlink derefence) as an open file in fd 3
- but we can't use it as-is as FEX (at least) doesn't support taking "pathname" (execve) as an open file descriptor.
- `C` and `F` are irrelevant here.

To support properly binary file already open as fd 3, FEX needs to be patched to use
`fexecve(3, argv, env)` kind of call when requested, it doesn't appear to support it yet.

Signed-off-by: Fabrice A. Marie <[email protected]>

Author: es-fabricemarie

src/main.rs

@@ -42,7 +42,7 @@ fn main() {
     trace!("Configuration:\n{:#?}", settings);
 
     // Collect command line arguments to pass through
-    let args: Vec<OsString> = env::args_os().skip(1).collect();
+    let mut args: Vec<OsString> = env::args_os().skip(1).collect();
     trace!("Args:\n{:#?}", args);
     if args.is_empty() {
         abort("No arguments passed, re-run with --help to learn more.");
@@ -60,13 +60,6 @@ fn main() {
         }
     }
 
-    // File descriptor 3 is where binfmt_misc typically passes the executable
-    let binary: PathBuf = read_link("/proc/self/fd/3").unwrap_or_else(|e| {
-        error!("Failed to read the executable from fd#3: {}", e);
-        exit(1);
-    });
-    trace!("Binary: {:#?}", binary);
-
     let mut interpreter_id = &settings.defaults.interpreter;
     for binary in settings.binaries.values() {
         if Path::new(&binary.path) == canonicalize(&args[0]).unwrap() {
@@ -156,8 +149,9 @@ fn main() {
         command = Command::new(interpreter_path);
     }
 
-    command.arg(binary);
-
+    let new_binary = args.remove(0);
+    args.remove(0);
+    command.arg(new_binary);
     // Pass through all the arguments
     command.args(&args);