add explicit types for mmap() flags

Author: mazunki

api/sys/mman.hpp

@@ -0,0 +1,30 @@
+/*
+ * provides namespaced types for `sys_mman(0p)` values
+ */
+#ifndef	_SYS_MMAN_HPP
+#define	_SYS_MMAN_HPP
+
+#include <cstdint>
+#include <sys/mman.h>
+#include <util/bitops.hpp>
+#include <type_traits>
+
+namespace os::mem {
+  enum class Flags : uint8_t {
+    None      = 0,
+    Shared    = MAP_SHARED,
+    Private   = MAP_PRIVATE,
+    Fixed     = MAP_FIXED,
+    Anonymous = MAP_ANONYMOUS,
+  };
+} // os::mmap
+
+
+namespace util {
+  inline namespace bitops {
+    template<> struct enable_bitmask_ops<os::mem::Flags> {
+      using type = std::underlying_type<os::mem::Flags>::type;
+      static constexpr bool enable = true;
+    };
+  }
+

api/util/bitops.hpp

@@ -115,19 +115,34 @@ constexpr operator~(E flag){
 
 // bool has_flag(flag)
 template<typename E>
-constexpr typename std::enable_if<enable_bitmask_ops<E>::enable, bool>::type
+[[nodiscard]] constexpr typename std::enable_if<enable_bitmask_ops<E>::enable, bool>::type
 has_flag(E flag){
   using base_type = typename std::underlying_type<E>::type;
   return static_cast<base_type>(flag);
 }
 
 // bool has_flag(field, flags)
 template<typename E>
-constexpr typename std::enable_if<enable_bitmask_ops<E>::enable, bool>::type
+[[nodiscard]] constexpr typename std::enable_if<enable_bitmask_ops<E>::enable, bool>::type
 has_flag(E field, E flags){
   return (field & flags) == flags ;
 }
 
+// bool missing_flag(flag)
+template<typename E>
+[[nodiscard]] constexpr typename std::enable_if<enable_bitmask_ops<E>::enable, bool>::type
+missing_flag(E flag){
+  using base_type = typename std::underlying_type<E>::type;
+  return static_cast<base_type>(flag) == 0;
+}
+
+// bool missing_flag(field, flags)
+template<typename E>
+[[nodiscard]] constexpr typename std::enable_if<enable_bitmask_ops<E>::enable, bool>::type
+missing_flag(E field, E flags) noexcept {
+  return (field & flags) != flags;
+}
+
 
 // Enable for uint8_t
 template<>

src/musl/mmap.cpp

@@ -1,6 +1,6 @@
 #include "common.hpp"
 #include <cstdint>
-#include <sys/mman.h>
+#include <sys/mman.hpp>
 #include <errno.h>
 #include <util/alloc_buddy.hpp>
 #include <os>
@@ -54,9 +54,11 @@ uintptr_t mmap_allocation_end() {
   return alloc->highest_used();
 }
 
-static void* sys_mmap(void * addr, size_t length, int /*prot*/, int flags,
+static void* sys_mmap(void * addr, size_t length, int /*prot*/, int _flags,
                       int fd, off_t /*offset*/)
 {
+  using os::mmap::Flags;
+  const Flags flags = static_cast<Flags>(_flags);
 
   // TODO: Implement minimal functionality to be POSIX compliant
   // https://pubs.opengroup.org/onlinepubs/009695399/functions/mmap.html
@@ -68,37 +70,38 @@ static void* sys_mmap(void * addr, size_t length, int /*prot*/, int flags,
     return MAP_FAILED;
   }
 
-  if ((flags & MAP_ANONYMOUS) == 0) {
+  if (util::missing_flag(flags, Flags::Anonymous)) {
     Expects(false && "We only support MAP_ANONYMOUS calls to mmap()");
     errno = ENOTSUP;
     return MAP_FAILED;
   }
 
-  if ((flags & MAP_FIXED) > 0) {
+  if (util::has_flag(flags, Flags::Fixed)) {
     Expects(false && "MAP_FIXED not supported.");
     errno = ENOTSUP;
     return MAP_FAILED;
   }
 
-  if (((flags & MAP_PRIVATE) > 0) && ((flags & MAP_ANONYMOUS) == 0)) {
-    Expects(false && "MAP_PRIVATE only supported for MAP_ANONYMOUS");
+  if (util::has_flag(flags, Flags::Private) && util::missing_flag(flags, Flags::Anonymous)) {
+    Expects(false && "MAP_PRIVATE only supported for MAP_ANONYMOS");
     errno = ENOTSUP;
     return MAP_FAILED;
   }
 
-  if (((flags & MAP_PRIVATE) > 0) && (addr != 0)) {
+  if (util::has_flag(flags, Flags::Private) && (addr != 0)) {
     Expects(false && "MAP_PRIVATE only supported for new allocations (address=0).");
     errno = ENOTSUP;
     return MAP_FAILED;
   }
 
-  if (((flags & MAP_SHARED) == 0) && ((flags & MAP_PRIVATE) == 0)) {
+  if (util::missing_flag(flags, Flags::Shared) && util::missing_flag(flags, Flags::Private)) {
     Expects(false && "MAP_SHARED or MAP_PRIVATE must be set.");
     errno = ENOTSUP;
     return MAP_FAILED;
   }
 
   // If we get here, the following should be true:
+  //
   // MAP_ANONYMOUS set + MAP_SHARED or MAP_PRIVATE
   // fd should be 0, address should be 0 for MAP_PRIVATE
   // (address is in any case ignored)