[libc][POSIX][unistd] Implement gethostname (#128142)

The implementation is based on the specifications from:
https://man7.org/linux/man-pages/man2/gethostname.2.html

Closes https://github.com/llvm/llvm-project/issues/126602

---------

Signed-off-by: ZakyHermawan <zaky.hermawan9615@gmail.com>

libc/config/linux/aarch64/entrypoints.txt

@@ -332,6 +332,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.getcwd
     libc.src.unistd.getentropy
     libc.src.unistd.geteuid
+    libc.src.unistd.gethostname
     libc.src.unistd.getpid
     libc.src.unistd.getppid
     libc.src.unistd.getsid

libc/config/linux/riscv/entrypoints.txt

@@ -336,6 +336,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.getcwd
     libc.src.unistd.getentropy
     libc.src.unistd.geteuid
+    libc.src.unistd.gethostname
     libc.src.unistd.getpid
     libc.src.unistd.getppid
     libc.src.unistd.getsid

libc/config/linux/x86_64/entrypoints.txt

@@ -338,6 +338,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.getcwd
     libc.src.unistd.getentropy
     libc.src.unistd.geteuid
+    libc.src.unistd.gethostname
     libc.src.unistd.getpid
     libc.src.unistd.getppid
     libc.src.unistd.getsid

libc/include/unistd.yaml

@@ -141,6 +141,13 @@ functions:
     return_type: uid_t
     arguments:
       - type: void
+  - name: gethostname
+    standards:
+      - POSIX
+    return_type: int
+    arguments:
+      - type: char *
+      - type: size_t
   - name: getopt
     standards:
       - POSIX

libc/src/unistd/CMakeLists.txt

@@ -111,6 +111,13 @@ add_entrypoint_object(
     .${LIBC_TARGET_OS}.getcwd
 )
 
+add_entrypoint_object(
+  gethostname
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.gethostname
+)
+
 add_entrypoint_object(
   getpid
   ALIAS

libc/src/unistd/gethostname.h

@@ -0,0 +1,21 @@
+//===-- Implementation header for gethostname -------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_UNISTD_GETHOSTNAME_H
+#define LLVM_LIBC_SRC_UNISTD_GETHOSTNAME_H
+
+#include "hdr/types/size_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int gethostname(char *name, size_t len);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_UNISTD_GETHOSTNAME_H

libc/src/unistd/linux/CMakeLists.txt

@@ -194,6 +194,20 @@ add_entrypoint_object(
     libc.src.errno.errno
 )
 
+add_entrypoint_object(
+  gethostname
+  SRCS
+    gethostname.cpp
+  HDRS
+    ../gethostname.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.include.sys_syscall
+    libc.include.sys_utsname
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
 add_entrypoint_object(
   geteuid
   SRCS

libc/src/unistd/linux/gethostname.cpp

@@ -0,0 +1,53 @@
+//===-- 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/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/string/string_utils.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+#include <sys/utsname.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, gethostname, (char *name, size_t size)) {
+  // Check for invalid pointer
+  if (name == nullptr) {
+    libc_errno = EFAULT;
+    return -1;
+  }
+
+  // Because there is no SYS_gethostname syscall, we use uname to get the
+  // hostname.
+  utsname unameData;
+  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_uname, &unameData);
+  if (ret < 0) {
+    libc_errno = static_cast<int>(-ret);
+    return -1;
+  }
+
+  // Guarantee that the name will be null terminated.
+  // The amount of bytes copied is min(size + 1, strlen(nodename) + 1)
+  // +1 to account for the null terminator (the last copied byte is a NULL).
+  internal::strlcpy(name, unameData.nodename, size + 1);
+
+  // Checks if the length of the hostname was greater than or equal to size
+  if (internal::string_length(unameData.nodename) >= size) {
+    libc_errno = ENAMETOOLONG;
+    return -1;
+  }
+
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/test/src/unistd/CMakeLists.txt

@@ -408,6 +408,18 @@ add_libc_unittest(
     libc.test.UnitTest.ErrnoSetterMatcher
 )
 
+add_libc_unittest(
+  gethostname_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    gethostname_test.cpp
+  DEPENDS
+    libc.src.unistd.gethostname
+    libc.src.errno.errno
+    libc.test.UnitTest.ErrnoCheckingTest
+)
+
 add_libc_unittest(
   getpid_test
   SUITE

libc/test/src/unistd/gethostname_test.cpp

@@ -0,0 +1,31 @@
+//===-- Unittests for 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 "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcGetHostNameTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST(LlvmLibcGetHostNameTest, GetCurrHostName) {
+  char hostbuffer[1024];
+  int ret = LIBC_NAMESPACE::gethostname(hostbuffer, sizeof(hostbuffer));
+  ASSERT_NE(ret, -1);
+  ASSERT_ERRNO_SUCCESS();
+
+  ret = LIBC_NAMESPACE::gethostname(hostbuffer, 0);
+  ASSERT_EQ(ret, -1);
+  ASSERT_ERRNO_EQ(ENAMETOOLONG);
+
+  // test for invalid pointer
+  char *nptr = nullptr;
+  ret = LIBC_NAMESPACE::gethostname(nptr, 1);
+  ASSERT_EQ(ret, -1);
+  ASSERT_ERRNO_EQ(EFAULT);
+}