Trying to access pointer value from the Struct closes the application

[krll-kov]

I have a struct

class MODULEINFO extends Struct {
  external Pointer lpBaseOfDll;
  @Uint32()
  external int sizeOfImage;
  external Pointer entryPoint;
}

And a function

static getModuleInformation(int hProcess, int hModule) {
    final _getModuleInformation = _psapi.lookupFunction<
        Int32 Function(IntPtr hProcess, IntPtr hModule, Pointer<MODULEINFO> lpmodinfo, Int32 cb),
        int Function(int hProcess, int hModule, Pointer<MODULEINFO> lpmodinfo, int cb)>('GetModuleInformation');

    final mi = calloc<MODULEINFO>();
    final int dwSize = sizeOf<MODULEINFO>();

    int f = _getModuleInformation(hProcess, hModule, mi, dwSize);
    print(f); // Function succeeded with result 1

    print(mi.ref.lpBaseOfDll.cast<Int32>().elementAt(0).value); // Application just closes 
  }

When i try to print a value from the struct - application crashes without any errors. Am i doing something wrong or it's a bug?

[dcharkes]

Hi!

What does print(mi.ref.lpBaseOfDll) print? If that is an address that is not allocated or it is 0x0 (nullptr) and you're trying to access that, the application crashes with a segmentation fault because you're trying to access memory that your application has not allocated.

[krll-kov]

Hi!

What does print(mi.ref.lpBaseOfDll) print? If that is an address that is not allocated or it is 0x0 (nullptr) and you're trying to access that, the application crashes with a segmentation fault because you're trying to access memory that your application has not allocated.

flutter: Pointer NativeType>: address=0x35410000

[mraleph]

Is hProcess pointing to your current process or to some other process?

[krll-kov]

Is hProcess pointing to your current process or to some other process?

To some other process

[mraleph]

Then you need to use ReadProcessMemory. You can't directly dereference the pointer because it originates from virtual address space of an another process.

[krll-kov]

Then you need to use ReadProcessMemory. You can't directly dereference the pointer because it originates from virtual address space of an another process.

I have an issue with RPM - it does not work for some reason: halildurmus/win32#215. And i cannot find out the problem because GetLastError does not retrieve latest winapi error

[dcharkes]

@kirill-21 we're tracking that in dart-lang/sdk#38832.