[libc] Allow openat and creat to return fd 0.

[jtstogel]

Previously, if the open or openat syscalls returned 0 as a (valid) file descriptor, the creat and openat wrappers would erroneously return -1.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Jackson Stogel (jtstogel)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/166466.diff

1 Files Affected:

• (modified) libc/src/fcntl/linux/openat.cpp (+5-5)

diff --git a/libc/src/fcntl/linux/openat.cpp b/libc/src/fcntl/linux/openat.cpp
index b47ad1fb3bb0f..b80abe532e51c 100644
--- a/libc/src/fcntl/linux/openat.cpp
+++ b/libc/src/fcntl/linux/openat.cpp
@@ -32,11 +32,11 @@ LLVM_LIBC_FUNCTION(int, openat, (int dfd, const char *path, int flags, ...)) {
 
   int fd = LIBC_NAMESPACE::syscall_impl<int>(SYS_openat, dfd, path, flags,
                                              mode_flags);
-  if (fd > 0)
-    return fd;
-
-  libc_errno = -fd;
-  return -1;
+  if (fd < 0) {
+    libc_errno = -fd;
+    return -1;
+  }
+  return fd;
 }
 
 } // namespace LIBC_NAMESPACE_DECL

[vonosmas]

Thank you for the fix!

Before committing, lease expand the description a little bit to clarify why the previous behavior was incorrect.

[jtstogel]

I've updated this patch to also fix creat, which has the same issue.