add rx/fork utility

rx/CMakeLists.txt

@@ -7,6 +7,7 @@ add_library(${PROJECT_NAME} OBJECT
     src/die.cpp
     src/FileLock.cpp
     src/filesystem.cpp
+    src/fork.cpp
     src/hexdump.cpp
     src/Mappable.cpp
     src/mem.cpp

rx/include/rx/fork.hpp

@@ -0,0 +1,8 @@
+#pragma once
+
+#include <rx/Process.hpp>
+
+namespace rx {
+// Fork result: -1 on error, 0 in child, child PID in parent
+ProcessId fork();
+} // namespace rx

rx/src/fork.cpp

@@ -0,0 +1,149 @@
+#include <rx/fork.hpp>
+
+#ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
+#include <mutex>
+#include <windows.h>
+#else
+#include <unistd.h>
+#endif
+
+#ifdef _WIN32
+namespace {
+struct ClientId {
+  HANDLE UniqueProcess;
+  HANDLE UniqueThread;
+};
+
+struct SECTION_IMAGE_INFORMATION {
+  PVOID TransferAddress; // The address of the image entry point function.
+  ULONG ZeroBits; // The number of high-order address bits that must be zero in
+                  // the image base address.
+  SIZE_T MaximumStackSize; // The maximum stack size of threads from the PE file
+                           // header.
+  SIZE_T CommittedStackSize; // The initial stack size of threads from the PE
+                             // file header.
+  ULONG SubSystemType; // The image subsystem from the PE file header (e.g.,
+                       // Windows GUI, Windows CUI, POSIX).
+  union {
+    struct {
+      USHORT SubSystemMinorVersion;
+      USHORT SubSystemMajorVersion;
+    };
+    ULONG SubSystemVersion;
+  };
+  union {
+    struct {
+      USHORT MajorOperatingSystemVersion;
+      USHORT MinorOperatingSystemVersion;
+    };
+    ULONG OperatingSystemVersion;
+  };
+  USHORT ImageCharacteristics; // The image characteristics from the PE file
+                               // header.
+  USHORT DllCharacteristics;   // The DLL characteristics flags (e.g., ASLR, NX
+                               // compatibility).
+  USHORT Machine;              // The image architecture (e.g., x86, x64, ARM).
+  BOOLEAN ImageContainsCode;   // The image contains native executable code.
+  union {
+    UCHAR ImageFlags;
+    struct {
+      UCHAR ComPlusNativeReady
+          : 1; // The image contains precompiled .NET assembly generated by NGEN
+               // (Native Image Generator).
+      UCHAR ComPlusILOnly : 1; // the image contains only Microsoft Intermediate
+                               // Language (IL) assembly.
+      UCHAR ImageDynamicallyRelocated
+          : 1; // The image was mapped using a random base address rather than
+               // the preferred base address.
+      UCHAR ImageMappedFlat
+          : 1; // The image was mapped using a single contiguous region, rather
+               // than separate regions for each section.
+      UCHAR BaseBelow4gb : 1; // The image was mapped using a base address below
+                              // the 4 GB boundary.
+      UCHAR ComPlusPrefer32bit : 1; // The image prefers to run as a 32-bit
+                                    // process, even on a 64-bit system.
+      UCHAR Reserved : 2;
+    };
+  };
+  ULONG LoaderFlags; // Reserved by ntdll.dll for the Windows loader.
+  ULONG
+  ImageFileSize;  // The size of the image, in bytes, including all headers.
+  ULONG CheckSum; // The image file checksum, from the PE optional header.
+};
+
+struct RtlUserProcessInformation {
+  ULONG Length;
+  HANDLE Process;
+  HANDLE Thread;
+  ClientId ClientId;
+  SECTION_IMAGE_INFORMATION ImageInformation;
+};
+
+#define RTL_CLONE_PROCESS_FLAGS_CREATE_SUSPENDED 0x00000001
+#define RTL_CLONE_PROCESS_FLAGS_INHERIT_HANDLES 0x00000002
+#define RTL_CLONE_PROCESS_FLAGS_NO_SYNCHRONIZE 0x00000004
+
+using RtlCloneUserProcessFn = long(__stdcall *)(
+    ULONG Flags, PSECURITY_DESCRIPTOR ProcessSecurityDescriptor,
+    PSECURITY_DESCRIPTOR ThreadSecurityDescriptor, HANDLE DebugPort,
+    RtlUserProcessInformation *ProcessInformation);
+
+RtlCloneUserProcessFn getRtlClone() {
+  static auto fn = []() -> RtlCloneUserProcessFn {
+    if (auto mod = ::GetModuleHandleW(L"ntdll.dll")) {
+      return reinterpret_cast<RtlCloneUserProcessFn>(
+          ::GetProcAddress(mod, "RtlCloneUserProcess"));
+    }
+
+    return nullptr;
+  }();
+
+  return fn;
+}
+} // namespace
+#endif
+
+rx::ProcessId rx::fork() {
+#ifdef _WIN32
+  auto rtlClone = getRtlClone();
+  if (!rtlClone) {
+    return static_cast<ProcessId>(-1);
+  }
+
+  auto parentPid = ::GetCurrentProcessId();
+
+  RtlUserProcessInformation procInfo{};
+  procInfo.Length = sizeof(procInfo);
+
+  ULONG rtlFlags = RTL_CLONE_PROCESS_FLAGS_CREATE_SUSPENDED |
+                   RTL_CLONE_PROCESS_FLAGS_INHERIT_HANDLES;
+
+  const long status = rtlClone(rtlFlags, nullptr, nullptr, nullptr, &procInfo);
+
+  if (status < 0) {
+    return static_cast<ProcessId>(-1);
+  }
+
+  if (status == 0) {
+    // parent process
+    const DWORD childPid = ::GetProcessId(procInfo.Process);
+
+    if (procInfo.Thread) {
+      ::ResumeThread(procInfo.Thread);
+      ::CloseHandle(procInfo.Thread);
+    }
+
+    ::CloseHandle(procInfo.Process);
+    return static_cast<ProcessId>(childPid);
+  }
+
+  FreeConsole();
+  AttachConsole(parentPid);
+
+  // child process
+  return ProcessId{};
+#else
+  return static_cast<ProcessId>(::fork());
+#endif
+}