[libc][unistd] Implement setsid (#125704)

https://man7.org/linux/man-pages/man2/setsid.2.html

closes #124632

Author: krishna2803

libc/config/linux/aarch64/entrypoints.txt

@@ -341,6 +341,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.readlink
     libc.src.unistd.readlinkat
     libc.src.unistd.rmdir
+    libc.src.unistd.setsid
     libc.src.unistd.symlink
     libc.src.unistd.symlinkat
     libc.src.unistd.sysconf

libc/config/linux/riscv/entrypoints.txt

@@ -337,6 +337,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.readlink
     libc.src.unistd.readlinkat
     libc.src.unistd.rmdir
+    libc.src.unistd.setsid
     libc.src.unistd.symlink
     libc.src.unistd.symlinkat
     libc.src.unistd.sysconf

libc/config/linux/x86_64/entrypoints.txt

@@ -340,6 +340,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.readlink
     libc.src.unistd.readlinkat
     libc.src.unistd.rmdir
+    libc.src.unistd.setsid
     libc.src.unistd.symlink
     libc.src.unistd.symlinkat
     libc.src.unistd.sysconf

libc/include/unistd.yaml

@@ -275,6 +275,12 @@ functions:
       - type: const void *__restrict
       - type: void *
       - type: ssize_t
+  - name: setsid
+    standards:
+      - POSIX
+    return_type: pid_t
+    arguments:
+      - type: void
   - name: symlink
     standards:
       - POSIX

libc/src/unistd/CMakeLists.txt

@@ -231,6 +231,13 @@ add_entrypoint_object(
     .${LIBC_TARGET_OS}.rmdir
 )
 
+add_entrypoint_object(
+  setsid
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.setsid
+)
+
 add_entrypoint_object(
   symlink
   ALIAS

libc/src/unistd/linux/CMakeLists.txt

@@ -459,6 +459,18 @@ add_entrypoint_object(
     libc.src.errno.errno
 )
 
+add_entrypoint_object(
+  setsid
+  SRCS
+    setsid.cpp
+  HDRS
+    ../setsid.h
+  DEPENDS
+    libc.hdr.types.pid_t
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+)
+
 add_entrypoint_object(
   symlink
   SRCS

libc/src/unistd/linux/setsid.cpp

@@ -0,0 +1,24 @@
+//===-- Linux implementation of setsid-------------------------------------===//
+//
+// 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/setsid.h"
+
+#include "hdr/types/pid_t.h"
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(pid_t, setsid, ()) {
+  return LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_setsid);
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/unistd/setsid.h

@@ -0,0 +1,21 @@
+//===-- Implementation header for setsid ------------------------*- 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_GETPID_H
+#define LLVM_LIBC_SRC_UNISTD_GETPID_H
+
+#include "hdr/types/pid_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+pid_t setsid();
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_UNISTD_GETPID_H

libc/test/src/unistd/CMakeLists.txt

@@ -287,6 +287,16 @@ add_libc_unittest(
     libc.src.__support.CPP.string_view
 )
 
+add_libc_unittest(
+  setsid_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    setsid_test.cpp
+  DEPENDS
+    libc.src.unistd.setsid
+)
+
 add_libc_unittest(
   symlink_test
   SUITE

libc/test/src/unistd/setsid_test.cpp

@@ -0,0 +1,15 @@
+//===-- Unittests for setsid ----------------------------------------------===//
+//
+// 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/setsid.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcGetPidTest, SmokeTest) {
+  // setsid always succeeds. So, we just call it as a smoke test.
+  LIBC_NAMESPACE::setsid();
+}