A demo of how to collect information on basic .NET events from ETW.

dotnet_etw.c

#define AssemblyDCStart_V1 155
#define MethodLoadVerbose_V1 143

#include <windows.h>
#include <stdio.h>
#include <wbemidl.h>
#include <wmistr.h>
#include <evntrace.h>
#include <Evntcons.h>

static GUID ClrRuntimeProviderGuid = { 0xe13c0d23, 0xccbc, 0x4e12, { 0x93, 0x1b, 0xd9, 0xcc, 0x2e, 0xee, 0x27, 0xe4 } };

// Can be stopped with 'logman stop "dotnet trace" -etw'
const char name[] = "dotnet trace\0";

#pragma pack(1)
typedef struct _AssemblyLoadUnloadRundown_V1
{
	ULONG64 AssemblyID;
	ULONG64 AppDomainID;
	ULONG64 BindingID;
	ULONG AssemblyFlags;
	WCHAR FullyQualifiedAssemblyName[1];
} AssemblyLoadUnloadRundown_V1, *PAssemblyLoadUnloadRundown_V1;

typedef struct _MethodLoadVerbose_V1 
{
	ULONG64 MethodID;
	ULONG64 ModuleID;
	ULONG64 MethodStartAddress;
	DWORD MethodSize;
	DWORD MethodToken;
	DWORD MethodFlags;
	WCHAR MethodNameSpace[1];
} MethodLoadUnloadVerbose_V1, *PMethodLoadUnloadVerbose_V1;
#pragma pack()

static void NTAPI ProcessEvent(PEVENT_RECORD EventRecord) {

	PEVENT_HEADER eventHeader = &EventRecord->EventHeader;
	PEVENT_DESCRIPTOR eventDescriptor = &eventHeader->EventDescriptor;
	AssemblyLoadUnloadRundown_V1* assemblyUserData;
	MethodLoadUnloadVerbose_V1* methodUserData;

	switch (eventDescriptor->Id) {
		case AssemblyDCStart_V1:
			assemblyUserData = (AssemblyLoadUnloadRundown_V1*)EventRecord->UserData;
			wprintf(L"[%d] - Assembly: %s\n", eventHeader->ProcessId, assemblyUserData->FullyQualifiedAssemblyName);
			break;
		case MethodLoadVerbose_V1:
			methodUserData = (struct _MethodLoadVerbose_V1*)EventRecord->UserData;
			WCHAR* MethodNameSpace = methodUserData->MethodNameSpace;
			WCHAR* MethodName = (WCHAR*)(((char*)methodUserData->MethodNameSpace) + (lstrlenW(methodUserData->MethodNameSpace) * 2) + 2);
			WCHAR* MethodSignature = (WCHAR*)(((char*)MethodName) + (lstrlenW(MethodName) * 2) + 2);
			wprintf(L"[%d] - MethodNameSpace: %s\n", eventHeader->ProcessId, methodUserData->MethodNameSpace);
			wprintf(L"[%d] - MethodName: %s\n", eventHeader->ProcessId, MethodName);
			wprintf(L"[%d] - MethodSignature: %s\n", eventHeader->ProcessId, MethodSignature);
			break;
	}
}

int main(void)
{
	TRACEHANDLE hTrace = 0;
	ULONG result, bufferSize;
	EVENT_TRACE_LOGFILEA trace;
	EVENT_TRACE_PROPERTIES *traceProp;

	printf("ETW .NET Trace example - @_xpn_\n\n");

	memset(&trace, 0, sizeof(EVENT_TRACE_LOGFILEA));
	trace.ProcessTraceMode    = PROCESS_TRACE_MODE_REAL_TIME | PROCESS_TRACE_MODE_EVENT_RECORD;
	trace.LoggerName          = (LPSTR)name;
	trace.EventRecordCallback = (PEVENT_RECORD_CALLBACK)ProcessEvent;

	bufferSize = sizeof(EVENT_TRACE_PROPERTIES) + sizeof(name) + sizeof(WCHAR);

	traceProp = (EVENT_TRACE_PROPERTIES*)LocalAlloc(LPTR, bufferSize);
	traceProp->Wnode.BufferSize    = bufferSize;
	traceProp->Wnode.ClientContext = 2;
	traceProp->Wnode.Flags         = WNODE_FLAG_TRACED_GUID;
	traceProp->LogFileMode         = EVENT_TRACE_REAL_TIME_MODE | EVENT_TRACE_USE_PAGED_MEMORY;
	traceProp->LogFileNameOffset   = 0;
	traceProp->LoggerNameOffset    = sizeof(EVENT_TRACE_PROPERTIES);

	if ((result = StartTraceA(&hTrace, (LPCSTR)name, traceProp)) != ERROR_SUCCESS) {
		printf("[!] Error starting trace: %d\n", result);
		return 1;
	}

	if ((result = EnableTraceEx(
		&ClrRuntimeProviderGuid,
		NULL,
		hTrace,
		1,
		TRACE_LEVEL_VERBOSE,
		0x8 | 0x10, // LoaderKeyword | JITKeyword
		0,
		0,
		NULL
	)) != ERROR_SUCCESS) {
		printf("[!] Error EnableTraceEx\n");
		return 2;
	}

	hTrace = OpenTrace(&trace);
	if (hTrace == INVALID_PROCESSTRACE_HANDLE) {
		printf("[!] Error OpenTrace\n");
		return 3;
	}

	result = ProcessTrace(&hTrace, 1, NULL, NULL);
	if (result != ERROR_SUCCESS) {
		printf("[!] Error ProcessTrace\n");
		return 4;
	}

	return 0;
}

Keep getting: Even if I convert it like:

hTrace = OpenTrace((PEVENT_TRACE_LOGFILEW)&trace);

The error goes away, but either way, when executing it I get:

Do you have an idea on what might be the problem?

In case anybody has the same problem: The project needs to be compiled as ASCII (Multi Byte), not Unicode

This worked for me
hTrace = OpenTraceA(&trace);
instead of
hTrace = OpenTrace(&trace);

It seems the old signature has been retired in evntrace.h (i.e. commented out):

// OpenTrace(
//  _Inout_ PEVENT_TRACE_LOGFILE Logfile
//  );