[libc-commits] [libc] [libc][POSIX][unistd] Implement gethostname (PR #128142)

[Michael Jones via libc-commits]

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@@ -0,0 +1,60 @@
+//===-- Linux implementation of gethostname -------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/gethostname.h"
+
+#include "hdr/types/size_t.h"
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+#include "src/errno/libc_errno.h"
+#include "src/string/strlen.h"
+#include "src/string/strncpy.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+#include <sys/utsname.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+// Matching the behavior of glibc version 2.2 and later.
+// Copies up to len bytes from the returned nodename field into name.
+LLVM_LIBC_FUNCTION(int, gethostname, (char *name, size_t len)) {
+  // Check for invalid pointer
+  if (name == nullptr) {
+    libc_errno = EFAULT;
+    return -1;
+  }
+
+  struct utsname unameData;
+  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_uname, &unameData);
+
+  // Checks if the length of the nodename was greater than or equal to len, and
+  // if it is, then the function returns -1 with errno set to ENAMETOOLONG. In
+  // this case, a terminating null byte is not included in the returned name.
+  if (strlen(unameData.nodename) >= len) {
+    strncpy(name, unameData.nodename, len);
+    libc_errno = ENAMETOOLONG;
+    return -1;
+  }
+
+  // If the size of the array name is not large enough (less than the size of
+  // nodename with null termination), then anything might happen. In this case,
+  // what happens to the array name will be determined by the implementation of
+  // LIBC_NAMESPACE_DECL::strncpy
+  strncpy(name, unameData.nodename, len);
+
+  if (ret < 0) {
+    libc_errno = static_cast<int>(-ret);
+    return -1;
+  }
----------------
michaelrj-google wrote:

this check should probably be right after the syscall and before we start trying to read from the struct. If the syscall returns an error then the struct may not be initialized.

https://github.com/llvm/llvm-project/pull/128142