SimpleSetThreadName.c

#include <windows.h>
#include <wchar.h>
#pragma comment(lib, "ntdll.lib")
#define ThreadNameInformation 0x26

// mimic nt!UNICODE_STRING
// sizeof(UNICODE_STRING) must be 0x10 for the syscall to succeed.
typedef struct 
{
  WORD Length;
  WORD MaximumLength;
  DWORD Padding;
  DWORD64 Buffer;
} 
UNICODE_STRING, *PUNICODE_STRING;

int wmain(int argc, wchar_t** argv)
{
  DWORD dwTid = _wtoi(argv[1]);
  PWSTR lpMessageToStore = argv[2];
  HANDLE hThread = OpenThread(THREAD_SET_LIMITED_INFORMATION, FALSE, dwTid);
  if(!hThread) return -1;
  
  // will result in AllocatePoolWithTag(0x110, "ThNm")
  UNICODE_STRING target = {
    .Length = 0x100,
    .MaximumLength = 0x102,
    .Buffer = lpMessageToStore,
  };
  NtSetInformationThread(hThread, ThreadNameInformation, &target, 0x10);
  
  CloseHandle(hThread);
  return 0;
}