ARM64EC: Dynamically determine syscall numbers under wine

Takes advantage of the consistent alphabetical syscall ordering that
wine follows.

Source/Windows/ARM64EC/Module.cpp

@@ -69,10 +69,9 @@ uint32_t NtDllRedirectionLUTSize;
 
 // Wine doesn't support issuing direct system calls with SVC, and unlike Windows it doesn't have a 'stable' syscall number for NtContinue
 void* WineSyscallDispatcher;
-// TODO: this really shouldn't be hardcoded, once wine gains proper syscall thunks this can be dropped.
-uint64_t WineNtContinueSyscallId = 0x1a;
-uint64_t WineNtAllocateVirtualMemorySyscallId = 0xb;
-uint64_t WineNtProtectVirtualMemorySyscallId = 0x76;
+uint64_t WineNtContinueSyscallId;
+uint64_t WineNtAllocateVirtualMemorySyscallId;
+uint64_t WineNtProtectVirtualMemorySyscallId;
 
 NTSTATUS NtContinueNative(ARM64_NT_CONTEXT* NativeContext, BOOLEAN Alert);
 NTSTATUS NtAllocateVirtualMemoryNative(HANDLE, PVOID*, ULONG_PTR, SIZE_T*, ULONG, ULONG);
@@ -151,7 +150,6 @@ bool IsDispatcherAddress(uint64_t Address) {
 
 
 void FillNtDllLUTs(HMODULE NtDll) {
-  NtDllBase = reinterpret_cast<uintptr_t>(NtDll);
   ULONG Size;
   const auto* LoadConfig =
     reinterpret_cast<_IMAGE_LOAD_CONFIG_DIRECTORY64*>(RtlImageDirectoryEntryToData(NtDll, true, IMAGE_DIRECTORY_ENTRY_LOAD_CONFIG, &Size));
@@ -196,6 +194,32 @@ void PatchCallChecker() {
   WriteModuleRVA(Module, CHPEMetadata->__os_arm64x_dispatch_icall_cfg, &CheckCall);
 }
 
+// Fills in the syscall numbers necessary to call *Native variants of syscalls from FEX under wine.
+void ParseWineSyscallNumbers(HMODULE NtDll) {
+  ULONG Size;
+  const auto* Exports = reinterpret_cast<IMAGE_EXPORT_DIRECTORY*>(RtlImageDirectoryEntryToData(NtDll, true, IMAGE_DIRECTORY_ENTRY_EXPORT, &Size));
+  const auto* NameTable = reinterpret_cast<uint32_t*>(NtDllBase + Exports->AddressOfNames);
+
+  // Wine orders syscalls alphabetically, take advantage of that to find the syscall indices for those which we need to
+  // manually issue. Note that all functions starting with Nt besides NtGetTickCount are syscalls and the syscall ID must
+  // be incremented by 1 for each.
+  uint32_t CurSyscallId = 0;
+  for (uint32_t Idx = 0; Idx < Exports->NumberOfNames; Idx++) {
+    const char* Name = reinterpret_cast<const char*>(NtDllBase + NameTable[Idx]);
+    if (Name[0] == 'N' && Name[1] == 't' && strcmp(Name, "NtGetTickCount") != 0) {
+      if (strcmp(Name, "NtContinue") == 0) {
+        WineNtContinueSyscallId = CurSyscallId;
+      } else if (strcmp(Name, "NtAllocateVirtualMemory") == 0) {
+        WineNtAllocateVirtualMemorySyscallId = CurSyscallId;
+      } else if (strcmp(Name, "NtProtectVirtualMemory") == 0) {
+        WineNtProtectVirtualMemorySyscallId = CurSyscallId;
+      }
+
+      CurSyscallId++;
+    }
+  }
+}
+
 // Syscall thunks may have been patched before FEX has loaded, the default call checker installed by ntdll into FEX will
 // try to invoke the JIT when calling such patched syscalls but this obviously doesn't work before FEX is initalised.
 // This function parses ntdll and sets up a custom call checker to prevent this, as such it must avoid using any syscall
@@ -204,9 +228,12 @@ void InitSyscalls() {
   // The ntdll exports called by GetModuleHandle/GetProcAddress aren't known to be patched before JIT init by any current
   // software so are safe to call, but if that changes the loader structures in the PEB could be parsed manually.
   const auto NtDll = GetModuleHandle("ntdll.dll");
+  NtDllBase = reinterpret_cast<uintptr_t>(NtDll);
+
   const auto WineSyscallDispatcherPtr = reinterpret_cast<void**>(GetProcAddress(NtDll, "__wine_syscall_dispatcher"));
   if (WineSyscallDispatcherPtr) {
     WineSyscallDispatcher = *WineSyscallDispatcherPtr;
+    ParseWineSyscallNumbers(NtDll);
   }
 
   FillNtDllLUTs(NtDll);