Type Cast Truncation from HANDLE to ULONG C++

问题

I am getting the warning (treated as error):

Type Cast Pointer Truncation from HANDLE to ULONG

When I try to compile, I understand that the type has a different length as I am compiling ARM64 rather than ARM, therefore I need to change the type or static_cast it, however I receive errors such as "expected (" when changing the line to something like this:

return static_cast<ULONG>PsGetProcessId(current_process); //this gives me invalid conversion type as 
                                                          //there are no brackets around the static cast 
                                                          //because I am returning its value

I add brackets, however there is always a problem and it never seems to work, always "Expected (":

return (static_cast<ULONG>)PsGetProcessId(current_process); //this bracket error

ORIGINAL CODE BELOW

ULONG memory::get_process_id_by_name(PEPROCESS start_process, const char* process_name)
{
    PLIST_ENTRY active_process_links;
    PEPROCESS current_process = start_process;

    do
    {
        PKPROCESS kproc = (PKPROCESS)current_process;
        PDISPATCHER_HEADER header = (PDISPATCHER_HEADER)kproc;
        LPSTR current_process_name = (LPSTR)((PUCHAR)current_process + IMAGE_FILE_NAME);

        if (header->SignalState == 0 && strcmp(current_process_name, process_name) == 0)
        {   
            return (ULONG)PsGetProcessId(current_process); //warning occurs here
        }

        active_process_links = (PLIST_ENTRY)((PUCHAR)current_process + ACTIVE_PROCESS_LINKS_FLINK);
        current_process = (PEPROCESS)(active_process_links->Flink);
        current_process = (PEPROCESS)((PUCHAR)current_process - ACTIVE_PROCESS_LINKS_FLINK);

    } while (start_process != current_process);

    return 0;
}

回答1:

The HANDLE type is used to point to an opaque structure.

It usually stores an index value, but in the winnt.h header file, it is defined as a pointer-length type.

typedef void *HANDLE;

So the correct approach is to treat the process id as a pointer-length type as well.

I know you don't like HANDLE, so you can use ULONG_PTR, it has the same length as the pointer type.

Here is the fixed code:

ULONG_PTR memory::get_process_id_by_name(PEPROCESS start_process, const char* process_name)
{
    PLIST_ENTRY active_process_links;
    PEPROCESS current_process = start_process;

    do
    {
        PKPROCESS kproc = (PKPROCESS)current_process;
        PDISPATCHER_HEADER header = (PDISPATCHER_HEADER)kproc;
        LPSTR current_process_name = (LPSTR)((PUCHAR)current_process + IMAGE_FILE_NAME);

        if (header->SignalState == 0 && strcmp(current_process_name, process_name) == 0)
        {
            return (ULONG_PTR)PsGetProcessId(current_process);
        }

        active_process_links = (PLIST_ENTRY)((PUCHAR)current_process + ACTIVE_PROCESS_LINKS_FLINK);
        current_process = (PEPROCESS)(active_process_links->Flink);
        current_process = (PEPROCESS)((PUCHAR)current_process - ACTIVE_PROCESS_LINKS_FLINK);

    } while (start_process != current_process);

    return 0;
}

If you have to use ULONG for other reasons, you can refer to @SoronelHaetir's solution.

Example for comment:

Before:

void test()
{
    ULONG value = (ULONG_PTR)0xFFFFFFFFFFFF;
    UNREFERENCED_PARAMETER(value);
}

EXTERN_C NTSTATUS DriverEntry(DRIVER_OBJECT *pDriverObject, UNICODE_STRING *pRegistryPath)
{
    UNREFERENCED_PARAMETER(pDriverObject);
    UNREFERENCED_PARAMETER(pRegistryPath);
    test();
    return STATUS_UNSUCCESSFUL;
}

Warnings:

error C2220: the following warning is treated as an error
warning C4305: 'initializing': truncation from 'ULONG_PTR' to 'ULONG'
warning C4309: 'initializing': truncation of constant value
========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ==========

After:

#pragma warning(push)
#pragma warning(disable: 4305)
#pragma warning(disable: 4309)
void test()
{
    ULONG value = (ULONG_PTR)0xFFFFFFFFFFFF;
    UNREFERENCED_PARAMETER(value);
}
#pragma warning(pop)

EXTERN_C NTSTATUS DriverEntry(DRIVER_OBJECT *pDriverObject, UNICODE_STRING *pRegistryPath)
{
    UNREFERENCED_PARAMETER(pDriverObject);
    UNREFERENCED_PARAMETER(pRegistryPath);
    test();
    return STATUS_UNSUCCESSFUL;
}

No warnings:

========== Rebuild All: 1 succeeded, 0 failed, 0 skipped ==========

回答2:

Use ULONG_PTR instead of ULONG:

static_cast<ULONG_PTR>(hHandle)

If the value the handle holds is actually meant to be used as a ULONG then cast the ULONG_PTR to ULONG:

static_cast<ULONG>(static_cast<ULONG_PTR>(hHandle))

来源：https://stackoverflow.com/questions/65351035/type-cast-truncation-from-handle-to-ulong-c

标签

c++

type-conversion

kernel

driver