OpenBSD: current_exe() fails when bin resolved through $PATH

[kpcyrd]

I've noticed std::env::current_exe() on openbsd depends on argv[0], which means the resolution only works if the binary was started with a relative or absolute path, but not when it was resolved by the shell using $PATH.

rust/src/libstd/sys/unix/os.rs

Lines 260 to 286 in 9ebf478

	#[cfg(any(target_os = "bitrig", target_os = "openbsd"))]
	pub fn current_exe() -> io::Result<PathBuf> {
	unsafe {
	let mut mib = [libc::CTL_KERN,
	libc::KERN_PROC_ARGS,
	libc::getpid(),
	libc::KERN_PROC_ARGV];
	let mib = mib.as_mut_ptr();
	let mut argv_len = 0;
	cvt(libc::sysctl(mib, 4, ptr::null_mut(), &mut argv_len,
	ptr::null_mut(), 0))?;
	let mut argv = Vec::<*const libc::c_char>::with_capacity(argv_len as usize);
	cvt(libc::sysctl(mib, 4, argv.as_mut_ptr() as *mut _,
	&mut argv_len, ptr::null_mut(), 0))?;
	argv.set_len(argv_len as usize);
	if argv[0].is_null() {
	return Err(io::Error::new(io::ErrorKind::Other,
	"no current exe available"))
	}
	let argv0 = CStr::from_ptr(argv[0]).to_bytes();
	if argv0[0] == b'.' || argv0.iter().any(|b| *b == b'/') {
	crate::fs::canonicalize(OsStr::from_bytes(argv0))
	} else {
	Ok(PathBuf::from(OsStr::from_bytes(argv0)))
	}
	}
	}

[kpcyrd]

Note that the code in rust upstream silently defaults to a wrong path (simply the program name in the current working directory), while openbsd downstream applies a patch to make this fail explicitly:

$OpenBSD: patch-src_libstd_sys_unix_os_rs,v 1.10 2019/03/11 19:13:40 semarie Exp $
argv0 isn't suitable as current_exe() in all cases.
Index: src/libstd/sys/unix/os.rs
--- src/libstd/sys/unix/os.rs.orig
+++ src/libstd/sys/unix/os.rs
@@ -273,13 +273,14 @@ pub fn current_exe() -> io::Result<PathBuf> {
         argv.set_len(argv_len as usize);
         if argv[0].is_null() {
             return Err(io::Error::new(io::ErrorKind::Other,
-                                      "no current exe available"))
+                                      "no current exe available (null)"))
         }
         let argv0 = CStr::from_ptr(argv[0]).to_bytes();
         if argv0[0] == b'.' || argv0.iter().any(|b| *b == b'/') {
             ::fs::canonicalize(OsStr::from_bytes(argv0))
         } else {
-            Ok(PathBuf::from(OsStr::from_bytes(argv0)))
+            Err(io::Error::new(io::ErrorKind::Other,
+                               "no current exe available (short)"))
         }
     }
 }

Unfortunately this patch doesn't give me the real path either.

[reynoldsbd]

Looks like the person who added this patch is on GitHub. @semarie can you share some context for why this patch is necessary on OpenBSD?

[semarie]

under OpenBSD, you have no standard way to retreive the path of the running executable.

basically it means env::current_exe() couldn't return useful thing on OpenBSD, but at design time it was just ignored (as 1-tier platform provides mostly accurate value in usual cases).

the patch on the OpenBSD ports is here to hard fail instead of silenciously use a potential wrong path.