vm: fix mapping of file's last page

thanks @red_prig for investigation

rx/CMakeLists.txt

@@ -4,9 +4,18 @@ find_package(Git)
 
 
 add_library(${PROJECT_NAME} OBJECT
+    src/mem.cpp
     src/Version.cpp
 )
-target_include_directories(${PROJECT_NAME} PUBLIC include)
+
+target_include_directories(${PROJECT_NAME}
+PUBLIC
+    include
+
+PRIVATE
+    include/${PROJECT_NAME}
+)
+
 
 execute_process(COMMAND date +%+4Y%m%d OUTPUT_VARIABLE RAW_VERSION)
 string(STRIP "${RAW_VERSION}" RAW_VERSION)

rx/include/rx/mem.hpp

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <cstddef>
+
+namespace rx::mem {
+extern const std::size_t pageSize;
+void *map(void *address, std::size_t size, int prot, int flags, int fd = -1,
+          std::ptrdiff_t offset = 0);
+void *reserve(std::size_t size);
+bool reserve(void *address, std::size_t size);
+bool protect(void *address, std::size_t size, int prot);
+bool unmap(void *address, std::size_t size);
+} // namespace rx::mem

rx/src/mem.cpp

@@ -0,0 +1,27 @@
+#include "mem.hpp"
+#include <sys/mman.h>
+#include <unistd.h>
+
+extern const std::size_t rx::mem::pageSize = sysconf(_SC_PAGE_SIZE);
+
+void *rx::mem::map(void *address, std::size_t size, int prot, int flags,
+                   int fd, std::ptrdiff_t offset) {
+  return ::mmap(address, size, prot, flags, fd, offset);
+}
+
+void *rx::mem::reserve(std::size_t size) {
+  return map(nullptr, size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS);
+}
+
+bool rx::mem::reserve(void *address, std::size_t size) {
+  return map(address, size, PROT_NONE,
+             MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED) != MAP_FAILED;
+}
+
+bool rx::mem::protect(void *address, std::size_t size, int prot) {
+  return ::mprotect(address, size, prot) == 0;
+}
+
+bool rx::mem::unmap(void *address, std::size_t size) {
+  return ::munmap(address, size) == 0;
+}