VC++ 中的内联汇编代码 :: 对 WaitForSingleObject 的系统调用需要帮助

Question

I have coded in VS2019 using VC++ and compiled using the Intel C++ compiler, a 64 bit command line music file player to play WAV files using WASAPI. The OS is Win 7-SP1.

This is the part of code on which I have questions and need help on. Declaration of variables are left out for conciseness.

// activate an IAudioClient
IAudioClient* pAudioClient;

...
...

// create an event
HANDLE hNeedDataEvent = CreateEvent(NULL, FALSE, FALSE, NULL);

// set the event handle
hr = pAudioClient->SetEventHandle(hNeedDataEvent);

...
...

//works fine
do
{
    WaitForSingleObject(hNeedDataEvent, INFINITE);

    hr = pAudioRenderClient->ReleaseBuffer(nFramesInBuffer, 0);
    hr = pAudioRenderClient->GetBuffer(nFramesInBuffer, &pData);

    memcpy(pData, sound_buffer + nBytesToSkip, nBytesThisPass);

    nBytesToSkip += nBytesThisPass;
} while (--nBuffersPlayed);

I want to replace the line of code: WaitForSingleObject(hNeedDataEvent, INFINITE); with inline Assembly code using a syscall. Portability is unimportant since this is just for experimentation/learning because have no knowledge of Assembler.

I found a syscall table for Win7-SP1 on Github and here's what it says for NtWaitForSingleObject:

; ULONG64 __stdcall NtWaitForSingleObject( ULONG64 arg_01 , ULONG64 arg_02 , ULONG64 arg_03 );
NtWaitForSingleObject PROC STDCALL 

    mov r10 , rcx
    mov eax , 1

    ;syscall
    db 0Fh , 05h

    ret
NtWaitForSingleObject ENDP

---

I think the inline Assembly code to replace the call to WaitForSingleObject should be:

__asm
{
    mov r10, ?????? ; pHandle
    xor edx, edx    ; FALSE: The alert cannot be delivered
    xor r8d, r8d    ; Time-out interval, in microseconds. NULL means infinite
    mov eax, 1      ; code number for WaitForSingleObject
    syscall
}

My questions are:

1. What exactly do I need to move to r10 so that it will contain the "handle" of the event?
2. Is the rest of the inline Assembly code correct?

As an aside, when I disassembled my compiled code I see this:

    mov     rcx, [rbp+220h+hHandle] ; hHandle
    mov     edx, 0FFFFFFFFh ; dwMilliseconds
    call    cs:WaitForSingleObject

Answer 1

__asm
{
   mov r10, hNeedDataEvent ; pHandle
   xor edx, edx ; FALSE: The alert cannot be delivered
   xor r8d, r8d ; Time-out interval, in microseconds. NULL means infinite
   mov eax, 1 ; code number for WaitForSingleObject syscall
}

I just assigned the value of hNeedDataEvent to r10 and it worked.