LibCore: Add functions to reserve and commit non-backed address space

Libraries/LibCore/System.cpp

@@ -142,6 +142,33 @@ ErrorOr<void> munmap(void* address, size_t size)
     return {};
 }
 
+ErrorOr<void*> reserve_address_space(size_t size)
+{
+    int flags = MAP_PRIVATE | MAP_ANONYMOUS;
+#ifdef MAP_NORESERVE
+    flags |= MAP_NORESERVE;
+#endif
+    auto* ptr = ::mmap(nullptr, size, PROT_NONE, flags, -1, 0);
+    if (ptr == MAP_FAILED)
+        return Error::from_syscall("mmap"sv, errno);
+    return ptr;
+}
+
+ErrorOr<void> commit_memory(void* address, size_t size)
+{
+    auto* ptr = ::mmap(address, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+    if (ptr == MAP_FAILED)
+        return Error::from_syscall("mmap"sv, errno);
+    return {};
+}
+
+ErrorOr<void> release_address_space(void* address, size_t size)
+{
+    if (::munmap(address, size) < 0)
+        return Error::from_syscall("munmap"sv, errno);
+    return {};
+}
+
 ErrorOr<int> anon_create([[maybe_unused]] size_t size, [[maybe_unused]] int options)
 {
     int fd = -1;

Libraries/LibCore/System.h

@@ -78,6 +78,9 @@ ErrorOr<struct stat> fstatat(int fd, StringView path, int flags);
 CORE_API ErrorOr<int> fcntl(int fd, int command, ...);
 ErrorOr<void*> mmap(void* address, size_t, int protection, int flags, int fd, off_t, size_t alignment = 0, StringView name = {});
 ErrorOr<void> munmap(void* address, size_t);
+CORE_API ErrorOr<void*> reserve_address_space(size_t size);
+CORE_API ErrorOr<void> commit_memory(void* address, size_t size);
+CORE_API ErrorOr<void> release_address_space(void* address, size_t size);
 ErrorOr<int> anon_create(size_t size, int options);
 CORE_API ErrorOr<int> open(StringView path, int options, mode_t mode = 0);
 ErrorOr<int> openat(int fd, StringView path, int options, mode_t mode = 0);

Libraries/LibCore/SystemWindows.cpp

@@ -199,6 +199,30 @@ ErrorOr<void> munmap(void* address, size_t size)
     return {};
 }
 
+ErrorOr<void*> reserve_address_space(size_t size)
+{
+    void* ptr = VirtualAlloc(nullptr, size, MEM_RESERVE, PAGE_NOACCESS);
+    if (!ptr)
+        return Error::from_windows_error();
+    return ptr;
+}
+
+ErrorOr<void> commit_memory(void* address, size_t size)
+{
+    if (!VirtualAlloc(address, size, MEM_COMMIT, PAGE_READWRITE))
+        return Error::from_windows_error();
+    return {};
+}
+
+ErrorOr<void> release_address_space(void* address, size_t size)
+{
+    // VirtualFree with MEM_RELEASE requires size == 0 and frees the entire reservation.
+    (void)size;
+    if (!VirtualFree(address, 0, MEM_RELEASE))
+        return Error::from_windows_error();
+    return {};
+}
+
 int getpid()
 {
     return GetCurrentProcessId();