[libc][mman] Implement msync (#84700)

Implement `msync` as specified in:

1. https://www.man7.org/linux/man-pages/man2/msync.2.html
2. https://pubs.opengroup.org/onlinepubs/9699919799/

Author: SchrodingerZhu

libc/config/linux/aarch64/entrypoints.txt

@@ -185,6 +185,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.mman.munlock
     libc.src.sys.mman.mlockall
     libc.src.sys.mman.munlockall
+    libc.src.sys.mman.msync
 
     # sys/random.h entrypoints
     libc.src.sys.random.getrandom

libc/config/linux/riscv/entrypoints.txt

@@ -190,6 +190,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.mman.munlock
     libc.src.sys.mman.mlockall
     libc.src.sys.mman.munlockall
+    libc.src.sys.mman.msync
 
     # sys/random.h entrypoints
     libc.src.sys.random.getrandom

libc/config/linux/x86_64/entrypoints.txt

@@ -228,6 +228,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.mman.munlock
     libc.src.sys.mman.mlockall
     libc.src.sys.mman.munlockall
+    libc.src.sys.mman.msync
 
     # sys/random.h entrypoints
     libc.src.sys.random.getrandom

libc/spec/posix.td

@@ -309,6 +309,11 @@ def POSIX : StandardSpec<"POSIX"> {
           RetValSpec<IntType>,
           [ArgSpec<VoidType>]
         >,
+        FunctionSpec<
+          "msync",
+          RetValSpec<IntType>,
+          [ArgSpec<VoidPtr>, ArgSpec<SizeTType>, ArgSpec<IntType>]
+        >,
       ]
   >;
 

libc/src/sys/mman/CMakeLists.txt

@@ -78,3 +78,10 @@ add_entrypoint_object(
   DEPENDS
     .${LIBC_TARGET_OS}.munlockall
 )
+
+add_entrypoint_object(
+  msync
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.msync
+)

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

@@ -139,3 +139,16 @@ add_entrypoint_object(
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
+
+add_entrypoint_object(
+  msync
+  SRCS
+    msync.cpp
+  HDRS
+    ../msync.h
+  DEPENDS
+    libc.include.sys_mman
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)

libc/src/sys/mman/linux/msync.cpp

@@ -0,0 +1,25 @@
+//===---------- Linux implementation of the msync 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/mman/msync.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, msync, (void *addr, size_t len, int flags)) {
+  long ret = syscall_impl(SYS_msync, cpp::bit_cast<long>(addr), len, flags);
+  if (ret < 0) {
+    libc_errno = static_cast<int>(-ret);
+    return -1;
+  }
+  return 0;
+}
+} // namespace LIBC_NAMESPACE

libc/src/sys/mman/msync.h

@@ -0,0 +1,21 @@
+//===-- Implementation header for msync function ----------------*- 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_MMAN_MSYNC_H
+#define LLVM_LIBC_SRC_SYS_MMAN_MSYNC_H
+
+#include <sys/mman.h>
+#include <sys/syscall.h>
+
+namespace LIBC_NAMESPACE {
+
+int msync(void *addr, size_t len, int flags);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_SYS_MMAN_MSYNC_H

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

@@ -107,3 +107,23 @@ add_libc_unittest(
     libc.src.unistd.sysconf
     libc.test.UnitTest.ErrnoSetterMatcher
 )
+
+add_libc_unittest(
+  msync_test
+  SUITE
+    libc_sys_mman_unittests
+  SRCS
+    msync_test.cpp
+  DEPENDS
+    libc.include.sys_mman
+    libc.include.unistd
+    libc.src.errno.errno
+    libc.src.sys.mman.mmap
+    libc.src.sys.mman.munmap
+    libc.src.sys.mman.msync
+    libc.src.sys.mman.mincore
+    libc.src.sys.mman.mlock
+    libc.src.sys.mman.munlock
+    libc.src.unistd.sysconf
+    libc.test.UnitTest.ErrnoSetterMatcher
+)

libc/test/src/sys/mman/linux/msync_test.cpp

@@ -0,0 +1,69 @@
+//===-- Unittests for msync -----------------------------------------------===//
+//
+// 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/mman/mlock.h"
+#include "src/sys/mman/mmap.h"
+#include "src/sys/mman/msync.h"
+#include "src/sys/mman/munlock.h"
+#include "src/sys/mman/munmap.h"
+#include "src/unistd/sysconf.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/LibcTest.h"
+#include "test/UnitTest/Test.h"
+
+using namespace LIBC_NAMESPACE::testing::ErrnoSetterMatcher;
+
+struct PageHolder {
+  size_t size;
+  void *addr;
+
+  PageHolder()
+      : size(LIBC_NAMESPACE::sysconf(_SC_PAGESIZE)),
+        addr(LIBC_NAMESPACE::mmap(nullptr, size, PROT_READ | PROT_WRITE,
+                                  MAP_ANONYMOUS | MAP_PRIVATE, -1, 0)) {}
+  ~PageHolder() {
+    if (addr != MAP_FAILED)
+      LIBC_NAMESPACE::munmap(addr, size);
+  }
+
+  char &operator[](size_t i) { return reinterpret_cast<char *>(addr)[i]; }
+
+  bool is_valid() { return addr != MAP_FAILED; }
+};
+
+TEST(LlvmLibcMsyncTest, UnMappedMemory) {
+  EXPECT_THAT(LIBC_NAMESPACE::msync(nullptr, 1024, MS_SYNC), Fails(ENOMEM));
+  EXPECT_THAT(LIBC_NAMESPACE::msync(nullptr, 1024, MS_ASYNC), Fails(ENOMEM));
+}
+
+TEST(LlvmLibcMsyncTest, LockedPage) {
+  PageHolder page;
+  ASSERT_TRUE(page.is_valid());
+  ASSERT_THAT(LIBC_NAMESPACE::mlock(page.addr, page.size), Succeeds());
+  EXPECT_THAT(
+      LIBC_NAMESPACE::msync(page.addr, page.size, MS_SYNC | MS_INVALIDATE),
+      Fails(EBUSY));
+  ASSERT_THAT(LIBC_NAMESPACE::munlock(page.addr, page.size), Succeeds());
+  EXPECT_THAT(LIBC_NAMESPACE::msync(page.addr, page.size, MS_SYNC), Succeeds());
+}
+
+TEST(LlvmLibcMsyncTest, UnalignedAddress) {
+  PageHolder page;
+  ASSERT_TRUE(page.is_valid());
+  EXPECT_THAT(LIBC_NAMESPACE::msync(&page[1], page.size - 1, MS_SYNC),
+              Fails(EINVAL));
+}
+
+TEST(LlvmLibcMsyncTest, InvalidFlag) {
+  PageHolder page;
+  ASSERT_TRUE(page.is_valid());
+  EXPECT_THAT(LIBC_NAMESPACE::msync(page.addr, page.size, MS_SYNC | MS_ASYNC),
+              Fails(EINVAL));
+  EXPECT_THAT(LIBC_NAMESPACE::msync(page.addr, page.size, -1), Fails(EINVAL));
+}