[libc] implement prctl (#74386)

Implement `prctl` as specified in
https://man7.org/linux/man-pages/man2/prctl.2.html.

This patch also includes test cases covering two simple use cases:

1. `PR_GET_NAME/PR_SET_NAME`: where userspace data is passed via arg2.
2. `PR_GET_THP_DISABLE`: where return value is passed via syscal retval.

Author: SchrodingerZhu

libc/config/linux/aarch64/entrypoints.txt

@@ -165,6 +165,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.wait.wait4
     libc.src.sys.wait.waitpid
 
+    # sys/prctl.h entrypoints
+    libc.src.sys.prctl.prctl
+
     # termios.h entrypoints
     libc.src.termios.cfgetispeed
     libc.src.termios.cfgetospeed

libc/config/linux/arm/entrypoints.txt

@@ -92,6 +92,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     # sys/mman.h entrypoints
     libc.src.sys.mman.mmap
     libc.src.sys.mman.munmap
+
+    # sys/prctl.h entrypoints
+    libc.src.sys.prctl.prctl
 )
 
 set(TARGET_LIBM_ENTRYPOINTS

libc/config/linux/riscv/entrypoints.txt

@@ -171,6 +171,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.wait.wait4
     libc.src.sys.wait.waitpid
 
+    # sys/prctl.h entrypoints
+    libc.src.sys.prctl.prctl
+
     # termios.h entrypoints
     libc.src.termios.cfgetispeed
     libc.src.termios.cfgetospeed

libc/config/linux/x86_64/entrypoints.txt

@@ -174,6 +174,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.wait.wait4
     libc.src.sys.wait.waitpid
 
+    # sys/prctl.h entrypoints
+    libc.src.sys.prctl.prctl
+
     # termios.h entrypoints
     libc.src.termios.cfgetispeed
     libc.src.termios.cfgetospeed

libc/include/sys/prctl.h.def

@@ -15,8 +15,6 @@
 // the macros itself.
 #include <linux/prctl.h>
 
-// TODO: Define the prctl macros.
-
 %%public_api()
 
 #endif // LLVM_LIBC_SYS_PRCTL_H

libc/src/sys/CMakeLists.txt

@@ -7,3 +7,4 @@ add_subdirectory(sendfile)
 add_subdirectory(stat)
 add_subdirectory(utsname)
 add_subdirectory(wait)
+add_subdirectory(prctl)

libc/src/sys/prctl/CMakeLists.txt

@@ -0,0 +1,10 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+endif()
+
+add_entrypoint_object(
+  prctl
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.prctl
+)

libc/src/sys/prctl/linux/CMakeLists.txt

@@ -0,0 +1,12 @@
+add_entrypoint_object(
+  prctl
+  SRCS
+    prctl.cpp
+  HDRS
+    ../prctl.h
+  DEPENDS
+    libc.include.sys_prctl
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)

libc/src/sys/prctl/linux/prctl.cpp

@@ -0,0 +1,37 @@
+//===---------- Linux implementation of the prctl function ----------------===//
+//
+// 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/sys/prctl/prctl.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+
+#include "src/errno/libc_errno.h"
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(int, prctl,
+                   (int option, unsigned long arg2, unsigned long arg3,
+                    unsigned long arg4, unsigned long arg5)) {
+  long ret =
+      LIBC_NAMESPACE::syscall_impl(SYS_prctl, option, arg2, arg3, arg4, arg5);
+  // The manpage states that "... return the nonnegative values described
+  // above. All other option values return 0 on success. On error,
+  // -1 is returned, and errno is set to indicate the error."
+  // According to the kernel implementation
+  // (https://github.com/torvalds/linux/blob/bee0e7762ad2c6025b9f5245c040fcc36ef2bde8/kernel/sys.c#L2442),
+  // return value from the syscall is set to 0 on default so we do not need to
+  // set the value on success manually.
+  if (ret < 0) {
+    libc_errno = static_cast<int>(-ret);
+    return -1;
+  }
+  return static_cast<int>(ret);
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/sys/prctl/prctl.h

@@ -0,0 +1,21 @@
+//===-- Implementation header for prctl ---------------------------*-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_SYS_PRCTL_PRCTL_H
+#define LLVM_LIBC_SRC_SYS_PRCTL_PRCTL_H
+
+#include <sys/prctl.h>
+
+namespace LIBC_NAMESPACE {
+
+int prctl(int option, unsigned long arg2, unsigned long arg3,
+          unsigned long arg4, unsigned long arg5);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_SYS_PRCTL_PRCTL_H

libc/test/src/sys/CMakeLists.txt

@@ -7,3 +7,4 @@ add_subdirectory(socket)
 add_subdirectory(stat)
 add_subdirectory(utsname)
 add_subdirectory(wait)
+add_subdirectory(prctl)

libc/test/src/sys/prctl/CMakeLists.txt

@@ -0,0 +1,3 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${LIBC_TARGET_OS})
+endif()

libc/test/src/sys/prctl/linux/CMakeLists.txt

@@ -0,0 +1,14 @@
+add_custom_target(libc_sys_prctl_unittests)
+
+add_libc_unittest(
+  prctl_test
+  SUITE
+    libc_sys_prctl_unittests
+  SRCS
+    prctl_test.cpp
+  DEPENDS
+    libc.include.sys_prctl
+    libc.include.errno
+    libc.src.sys.prctl.prctl
+    libc.src.errno.errno
+)

libc/test/src/sys/prctl/linux/prctl_test.cpp

@@ -0,0 +1,44 @@
+//===-- Unittests for prctl -----------------------------------------------===//
+//
+// 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/errno/libc_errno.h"
+#include "src/sys/prctl/prctl.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include <errno.h>
+#include <sys/prctl.h>
+
+using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Fails;
+using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
+
+TEST(LlvmLibcSysPrctlTest, GetSetName) {
+  char name[17];
+  unsigned long name_addr = 0;
+  ASSERT_THAT(LIBC_NAMESPACE::prctl(PR_GET_NAME, name_addr, 0, 0, 0),
+              Fails(EFAULT, -1));
+
+  name_addr = reinterpret_cast<unsigned long>("libc-test");
+  ASSERT_THAT(LIBC_NAMESPACE::prctl(PR_SET_NAME, name_addr, 0, 0, 0),
+              Succeeds());
+
+  name_addr = reinterpret_cast<unsigned long>(name);
+  ASSERT_THAT(LIBC_NAMESPACE::prctl(PR_GET_NAME, name_addr, 0, 0, 0),
+              Succeeds());
+  ASSERT_STREQ(name, "libc-test");
+}
+
+TEST(LlvmLibcSysPrctlTest, GetTHPDisable) {
+  // Manually check errno since the return value logic here is not
+  // covered in ErrnoSetterMatcher.
+  libc_errno = 0;
+  int ret = LIBC_NAMESPACE::prctl(PR_GET_THP_DISABLE, 0, 0, 0, 0);
+  ASSERT_EQ(libc_errno, 0);
+  // PR_GET_THP_DISABLE return (as the function result) the current
+  // setting of the "THP disable" flag for the calling thread, which
+  // is either 1, if the flag is set; or 0, if it is not.
+  ASSERT_TRUE(ret == 0 || ret == 1);
+}