[libc] Add sys/mman syscall wrappers (#195103)

Added ErrorOr-returning syscall wrappers for mmap, munmap, mprotect, and
pkey_mprotect in src/__support/OSUtil/linux/syscall_wrappers/. Migrated
the sys/mman Linux entrypoint implementations to use them, following the
design in libc/docs/dev/syscall_wrapper_refactor.rst.

Removed the shared mprotect_common.h in favour of per-syscall wrapper
headers. Added hdr/sys_mman_macros.h proxy header.

libc/hdr/CMakeLists.txt

@@ -185,6 +185,15 @@ add_proxy_header_library(
     libc.include.llvm-libc-macros.sys_stat_macros
 )
 
+add_proxy_header_library(
+  sys_mman_macros
+  HDRS
+    sys_mman_macros.h
+  FULL_BUILD_DEPENDS
+    libc.include.sys_mman
+    libc.include.llvm-libc-macros.sys_mman_macros
+)
+
 add_header_library(unistd_overlay HDRS unistd_overlay.h)
 add_proxy_header_library(
   unistd_macros

libc/hdr/sys_mman_macros.h

@@ -0,0 +1,22 @@
+//===-- Definition of macros from sys/mman.h ------------------------------===//
+//
+// 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_HDR_SYS_MMAN_MACROS_H
+#define LLVM_LIBC_HDR_SYS_MMAN_MACROS_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-macros/sys-mman-macros.h"
+
+#else // Overlay mode
+
+#include <sys/mman.h>
+
+#endif // LLVM_LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_SYS_MMAN_MACROS_H

libc/src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt

@@ -185,3 +185,53 @@ add_header_library(
     libc.hdr.types.struct_timespec
     libc.include.sys_syscall
 )
+
+add_header_library(
+  mmap
+  HDRS
+    mmap.h
+  DEPENDS
+    libc.src.__support.OSUtil.osutil
+    libc.src.__support.common
+    libc.src.__support.error_or
+    libc.src.__support.macros.config
+    libc.hdr.types.off_t
+    libc.include.sys_syscall
+)
+
+add_header_library(
+  munmap
+  HDRS
+    munmap.h
+  DEPENDS
+    libc.src.__support.OSUtil.osutil
+    libc.src.__support.common
+    libc.src.__support.error_or
+    libc.src.__support.macros.config
+    libc.include.sys_syscall
+)
+
+add_header_library(
+  mprotect
+  HDRS
+    mprotect.h
+  DEPENDS
+    libc.src.__support.OSUtil.osutil
+    libc.src.__support.common
+    libc.src.__support.error_or
+    libc.src.__support.macros.config
+    libc.include.sys_syscall
+)
+
+add_header_library(
+  pkey_mprotect
+  HDRS
+    pkey_mprotect.h
+  DEPENDS
+    libc.src.__support.OSUtil.osutil
+    libc.src.__support.common
+    libc.src.__support.error_or
+    libc.src.__support.macros.config
+    libc.hdr.errno_macros
+    libc.include.sys_syscall
+)

libc/src/__support/OSUtil/linux/syscall_wrappers/mmap.h

@@ -0,0 +1,59 @@
+//===-- Syscall wrapper for mmap --------------------------------*- 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___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MMAP_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MMAP_H
+
+#include "hdr/types/off_t.h"
+#include "src/__support/OSUtil/linux/syscall.h" // syscall_impl, linux_utils::is_valid_mmap
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include <linux/param.h> // For EXEC_PAGESIZE
+#include <sys/syscall.h> // For syscall numbers
+
+namespace LIBC_NAMESPACE_DECL {
+namespace linux_syscalls {
+
+LIBC_INLINE ErrorOr<void *> mmap(void *addr, size_t size, int prot, int flags,
+                                 int fd, off_t offset) {
+  // TODO: Perform POSIX-prescribed argument validation not done by the
+  // linux syscall.
+
+  // EXEC_PAGESIZE is used for the page size. While this is OK for x86_64,
+  // it might not be correct in general.
+  // TODO: Use pagesize read from the ELF aux vector instead of
+  // EXEC_PAGESIZE.
+#ifdef SYS_mmap2
+  offset /= EXEC_PAGESIZE;
+  long syscall_number = SYS_mmap2;
+#elif defined(SYS_mmap)
+  long syscall_number = SYS_mmap;
+#else
+#error "mmap or mmap2 syscalls not available."
+#endif
+
+  // Explicit cast to silence "implicit conversion loses integer precision"
+  // warnings when compiling for 32-bit systems.
+  long ret =
+      syscall_impl<long>(syscall_number, reinterpret_cast<long>(addr), size,
+                         prot, flags, fd, static_cast<long>(offset));
+
+  // A negative return value from the syscall can also be an error-free
+  // value returned by the syscall. However, since a valid return address
+  // cannot be within the last page, a return value corresponding to a
+  // location in the last page is an error value.
+  if (!linux_utils::is_valid_mmap(ret))
+    return Error(-static_cast<int>(ret));
+  return reinterpret_cast<void *>(ret);
+}
+
+} // namespace linux_syscalls
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MMAP_H

libc/src/__support/OSUtil/linux/syscall_wrappers/mprotect.h

@@ -0,0 +1,32 @@
+//===-- Syscall wrapper for mprotect ----------------------------*- 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___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MPROTECT_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MPROTECT_H
+
+#include "src/__support/OSUtil/linux/syscall.h" // syscall_impl
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include <sys/syscall.h> // For syscall numbers
+
+namespace LIBC_NAMESPACE_DECL {
+namespace linux_syscalls {
+
+LIBC_INLINE ErrorOr<int> mprotect(void *addr, size_t size, int prot) {
+  int ret =
+      syscall_impl<int>(SYS_mprotect, reinterpret_cast<long>(addr), size, prot);
+  if (ret < 0)
+    return Error(-ret);
+  return ret;
+}
+
+} // namespace linux_syscalls
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MPROTECT_H

libc/src/__support/OSUtil/linux/syscall_wrappers/munmap.h

@@ -0,0 +1,31 @@
+//===-- Syscall wrapper for munmap ------------------------------*- 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___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MUNMAP_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MUNMAP_H
+
+#include "src/__support/OSUtil/linux/syscall.h" // syscall_impl
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include <sys/syscall.h> // For syscall numbers
+
+namespace LIBC_NAMESPACE_DECL {
+namespace linux_syscalls {
+
+LIBC_INLINE ErrorOr<int> munmap(void *addr, size_t size) {
+  int ret = syscall_impl<int>(SYS_munmap, reinterpret_cast<long>(addr), size);
+  if (ret < 0)
+    return Error(-ret);
+  return ret;
+}
+
+} // namespace linux_syscalls
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_MUNMAP_H

libc/src/__support/OSUtil/linux/syscall_wrappers/pkey_mprotect.h

@@ -0,0 +1,38 @@
+//===-- Syscall wrapper for pkey_mprotect -----------------------*- 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___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_PKEY_MPROTECT_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_PKEY_MPROTECT_H
+
+#include "hdr/errno_macros.h"
+#include "src/__support/OSUtil/linux/syscall.h" // syscall_impl
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include <sys/syscall.h> // For syscall numbers
+
+namespace LIBC_NAMESPACE_DECL {
+namespace linux_syscalls {
+
+LIBC_INLINE ErrorOr<int> pkey_mprotect(void *addr, size_t len, int prot,
+                                       int pkey) {
+#if !defined(SYS_pkey_mprotect)
+  return Error(ENOSYS);
+#else
+  int ret = syscall_impl<int>(SYS_pkey_mprotect, reinterpret_cast<long>(addr),
+                              len, prot, pkey);
+  if (ret < 0)
+    return Error(-ret);
+  return ret;
+#endif
+}
+
+} // namespace linux_syscalls
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_PKEY_MPROTECT_H

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

@@ -25,9 +25,10 @@ add_entrypoint_object(
   HDRS
     ../mmap.h
   DEPENDS
-    libc.include.sys_mman
+    libc.hdr.sys_mman_macros
-    libc.include.sys_syscall
+    libc.hdr.types.size_t
-    libc.src.__support.OSUtil.osutil
+    libc.hdr.types.off_t
+    libc.src.__support.OSUtil.linux.syscall_wrappers.mmap
     libc.src.errno.errno
 )
 
@@ -51,23 +52,11 @@ add_entrypoint_object(
   HDRS
     ../munmap.h
   DEPENDS
-    libc.include.sys_mman
+    libc.hdr.types.size_t
-    libc.include.sys_syscall
+    libc.src.__support.OSUtil.linux.syscall_wrappers.munmap
-    libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
-add_header_library(
-  mprotect_common
-  HDRS
-    mprotect_common.h
-  DEPENDS
-    libc.include.sys_syscall
-    libc.src.__support.OSUtil.osutil
-    libc.src.errno.errno
-    libc.src.__support.error_or
-)
-
 add_entrypoint_object(
   mprotect
   SRCS
@@ -75,11 +64,9 @@ add_entrypoint_object(
   HDRS
     ../mprotect.h
   DEPENDS
-    libc.include.sys_mman
+    libc.hdr.types.size_t
-    libc.include.sys_syscall
+    libc.src.__support.OSUtil.linux.syscall_wrappers.mprotect
-    libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
-    .mprotect_common
 )
 
 add_entrypoint_object(
@@ -240,11 +227,10 @@ add_entrypoint_object(
   HDRS
     ../pkey_mprotect.h
   DEPENDS
-    libc.include.sys_mman
+    libc.hdr.types.size_t
-    libc.include.sys_syscall
+    libc.src.__support.OSUtil.linux.syscall_wrappers.mprotect
-    libc.src.__support.OSUtil.osutil
+    libc.src.__support.OSUtil.linux.syscall_wrappers.pkey_mprotect
     libc.src.errno.errno
-    .mprotect_common
 )
 
 add_entrypoint_object(

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

@@ -7,61 +7,24 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/sys/mman/mmap.h"
+#include "hdr/sys_mman_macros.h"
 
-#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/OSUtil/linux/syscall_wrappers/mmap.h"
 #include "src/__support/common.h"
-
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
-#include <linux/param.h> // For EXEC_PAGESIZE.
-#include <sys/syscall.h> // For syscall numbers.
 
 namespace LIBC_NAMESPACE_DECL {
 
-// This function is currently linux only. It has to be refactored suitably if
-// mmap is to be supported on non-linux operating systems also.
 LLVM_LIBC_FUNCTION(void *, mmap,
                    (void *addr, size_t size, int prot, int flags, int fd,
                     off_t offset)) {
-  // A lot of POSIX standard prescribed validation of the parameters is not
+  auto result = linux_syscalls::mmap(addr, size, prot, flags, fd, offset);
-  // done in this function as modern linux versions do it in the syscall.
+  if (!result) {
-  // TODO: Perform argument validation not done by the linux syscall.
+    libc_errno = result.error();
-
-  // EXEC_PAGESIZE is used for the page size. While this is OK for x86_64, it
-  // might not be correct in general.
-  // TODO: Use pagesize read from the ELF aux vector instead of EXEC_PAGESIZE.
-
-#ifdef SYS_mmap2
-  offset /= EXEC_PAGESIZE;
-  long syscall_number = SYS_mmap2;
-#elif defined(SYS_mmap)
-  long syscall_number = SYS_mmap;
-#else
-#error "mmap or mmap2 syscalls not available."
-#endif
-
-  // We add an explicit cast to silence a "implicit conversion loses integer
-  // precision" warning when compiling for 32-bit systems.
-  long mmap_offset = static_cast<long>(offset);
-  long ret =
-      LIBC_NAMESPACE::syscall_impl(syscall_number, reinterpret_cast<long>(addr),
-                                   size, prot, flags, fd, mmap_offset);
-
-  // The mmap/mmap2 syscalls return negative values on error. These negative
-  // values are actually the negative values of the error codes. So, fix them
-  // up in case an error code is detected.
-  //
-  // A point to keep in mind for the fix up is that a negative return value
-  // from the syscall can also be an error-free value returned by the syscall.
-  // However, since a valid return address cannot be within the last page, a
-  // return value corresponding to a location in the last page is an error
-  // value.
-  if (!linux_utils::is_valid_mmap(ret)) {
-    libc_errno = static_cast<int>(-ret);
     return MAP_FAILED;
   }
-
+  return result.value();
-  return reinterpret_cast<void *>(ret);
 }
 
 } // namespace LIBC_NAMESPACE_DECL

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

@@ -8,25 +8,20 @@
 
 #include "src/sys/mman/mprotect.h"
 
-#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/OSUtil/linux/syscall_wrappers/mprotect.h"
 #include "src/__support/common.h"
-
-#include "src/__support/error_or.h"
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
-#include "src/sys/mman/linux/mprotect_common.h"
-#include <sys/syscall.h> // For syscall numbers.
 
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(int, mprotect, (void *addr, size_t size, int prot)) {
-  ErrorOr<int> result =
+  auto result = linux_syscalls::mprotect(addr, size, prot);
-      LIBC_NAMESPACE::mprotect_common::mprotect_impl(addr, size, prot);
+  if (!result) {
-  if (!result.has_value()) {
     libc_errno = result.error();
     return -1;
   }
-  return result.value();
+  return 0;
 }
 
 } // namespace LIBC_NAMESPACE_DECL

libc/src/sys/mman/linux/mprotect_common.h

@@ -1,38 +0,0 @@
-//===---------- Shared Linux implementation of POSIX mprotect. ------------===//
-//
-// 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/__support/OSUtil/syscall.h" // For internal syscall function.
-#include "src/__support/common.h"
-#include "src/__support/error_or.h"
-#include "src/__support/libc_errno.h"
-#include "src/__support/macros/attributes.h"
-#include "src/__support/macros/config.h"
-#include <sys/syscall.h> // For syscall numbers.
-
-namespace LIBC_NAMESPACE_DECL {
-
-namespace mprotect_common {
-
-// This function is currently linux only. It has to be refactored suitably if
-// mprotect is to be supported on non-linux operating systems also.
-LIBC_INLINE ErrorOr<int> mprotect_impl(void *addr, size_t size, int prot) {
-  int ret = LIBC_NAMESPACE::syscall_impl<int>(
-      SYS_mprotect, reinterpret_cast<long>(addr), size, prot);
-
-  // A negative return value indicates an error with the magnitude of the
-  // value being the error code.
-  if (ret < 0) {
-    return Error(-ret);
-  }
-
-  return 0;
-}
-
-} // namespace mprotect_common
-
-} // namespace LIBC_NAMESPACE_DECL

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

@@ -8,28 +8,19 @@
 
 #include "src/sys/mman/munmap.h"
 
-#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/OSUtil/linux/syscall_wrappers/munmap.h"
 #include "src/__support/common.h"
-
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
-#include <sys/syscall.h> // For syscall numbers.
 
 namespace LIBC_NAMESPACE_DECL {
 
-// This function is currently linux only. It has to be refactored suitably if
-// mmap is to be supported on non-linux operating systems also.
 LLVM_LIBC_FUNCTION(int, munmap, (void *addr, size_t size)) {
-  int ret = LIBC_NAMESPACE::syscall_impl<int>(
+  auto result = linux_syscalls::munmap(addr, size);
-      SYS_munmap, reinterpret_cast<long>(addr), size);
+  if (!result) {
-
+    libc_errno = result.error();
-  // A negative return value indicates an error with the magnitude of the
-  // value being the error code.
-  if (ret < 0) {
-    libc_errno = -ret;
     return -1;
   }
-
   return 0;
 }
 

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

@@ -8,51 +8,28 @@
 
 #include "src/sys/mman/pkey_mprotect.h"
 
-#include "hdr/errno_macros.h" // For ENOSYS
+#include "src/__support/OSUtil/linux/syscall_wrappers/mprotect.h"
-#include "hdr/types/size_t.h"
+#include "src/__support/OSUtil/linux/syscall_wrappers/pkey_mprotect.h"
-#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
-#include "src/__support/error_or.h"
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
-#include "src/sys/mman/linux/mprotect_common.h"
-
-#include <sys/syscall.h> // For syscall numbers.
 
 namespace LIBC_NAMESPACE_DECL {
-namespace internal {
-
-LIBC_INLINE ErrorOr<int> pkey_mprotect_impl(void *addr, size_t len, int prot,
-                                            int pkey) {
-  // Fall back to mprotect if pkey is -1
-  // to maintain compatibility with kernel versions that don't support pkey.
-  if (pkey == -1) {
-    return LIBC_NAMESPACE::mprotect_common::mprotect_impl(addr, len, prot);
-  }
-
-#if !defined(SYS_pkey_mprotect)
-  return Error(ENOSYS);
-#else
-  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_pkey_mprotect, addr, len,
-                                              prot, pkey);
-  if (ret < 0) {
-    return Error(-ret);
-  }
-  return 0;
-#endif
-}
-
-} // namespace internal
 
 LLVM_LIBC_FUNCTION(int, pkey_mprotect,
                    (void *addr, size_t len, int prot, int pkey)) {
-  ErrorOr<int> ret =
+  ErrorOr<int> ret(0);
-      LIBC_NAMESPACE::internal::pkey_mprotect_impl(addr, len, prot, pkey);
+  if (pkey == -1) {
-  if (!ret.has_value()) {
+    ret = linux_syscalls::mprotect(addr, len, prot);
+  } else {
+    ret = linux_syscalls::pkey_mprotect(addr, len, prot, pkey);
+  }
+
+  if (!ret) {
     libc_errno = ret.error();
     return -1;
   }
-  return ret.value();
+  return 0;
 }
 
 } // namespace LIBC_NAMESPACE_DECL