Keepassx fails to compile on FreeBSD due to libusb implementation differences

[madpilot78]

On FreeBSD the libusb_hotplug_register_callback() function uses a pointer to a struct as an handle.

I'm changing the methods to use this as expected by the system library.

This now compiles fine but fails at runtime.

Not sure why this patch is not working and I must admit I do not understand what is being done using qintptr in

keepassxc/src/gui/osutils/DeviceListener.h

Line 41 in f093291

typedef qintptr Handle;

.

This has been noticed here: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=277652

The failures with my patch are described here: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=277652#c10

I do not have a yubikey so I cannot do testing myself.

Thanks in advance for any help!

Testing strategy

As said, with this changes the source compiles on FreeBSD, and the resulting binary works, except when exercising the modified code.

Type of change

• ✅ Bug fix (non-breaking change that fixes an issue)

[phoerious]

Instead of adding all the ifdefs, you should cast libusb_hotplug_callback_handle to qintptr instead. This should already be an opaque pointer type that needs no additional logic.

[phoerious]

This is actually a bug and should be qintptr aka Handle.

[phoerious]

Same here.

[madpilot78]

@phoerious Thanks for the feedback!

So, if I understand correctly, there is an existing bug in the code that uses ints where it should be using qintptr. This makes some sense to me, now I can understand why qintptr was used to start with.

I'll do some testing hoping I can make sense of all this.

Thanks again for your suggestions.

[phoerious]

On a normal 64 bit system it shouldn't make a difference, but with smaller word lengths it may.

[madpilot78]

@phoerious Problem is, the code as is fails to compile on FreeBSD. FreeBSD is using recent clang by default, which tends to be less permissive about this kind of casts.

Putting the correct types in the correct place should be enough to make it compile and work then.

[madpilot78]

Hi again,

I experimented a little but made little progress.

I uploaded what I have now, following suggestion to use qintptr.

This fails to compile. If I use classic C style casts in place of static_cast it does compile but fails at runtime.

I'm asking for help on how to fix this. My limited C++ knowledge has already reached its limit.

Thanks in advance.

[droidmonkey]

Both your build and runtime error is here, you shouldn't reference the output of the static cast directly. Make the handle variable an int, then static cast the return call.

error: cannot take the address of an rvalue of type 'libusb_hotplug_callback_handle' (aka 'int')
        &static_cast<libusb_hotplug_callback_handle>(handle));
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[madpilot78]

Why int?

Please keep in mind that I'm trying to fix this in FreeBSD. FreeBSD has its own implementation of libusb. AFAIK other BSDs do too, but I have not checked.

FreeBSD's libusb_hotplug_callback_handle is defined as [1]:

typedef struct libusb_hotplug_callback_handle_struct *libusb_hotplug_callback_handle;

so the error I'm getting is:

/wrkdirs/usr/ports/security/keepassxc/work/keepassxc-2.7.8/src/gui/osutils/nixutils/DeviceListenerLibUsb.cpp:87:10: error: cannot cast from type 'Handle' (aka 'long long') to pointer type 'libusb_hotplug_callback_handle' (aka 'libusb_hotplug_callback_handle_struct *')
   87 |         &static_cast<libusb_hotplug_callback_handle>(handle));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/wrkdirs/usr/ports/security/keepassxc/work/keepassxc-2.7.8/src/gui/osutils/nixutils/DeviceListenerLibUsb.cpp:110:77: error: cannot cast from type 'Handle' (aka 'long long') to pointer type 'libusb_hotplug_callback_handle' (aka 'libusb_hotplug_callback_handle_struct *')
  110 |     libusb_hotplug_deregister_callback(static_cast<libusb_context*>(m_ctx), static_cast<libusb_hotplug_callback_handle>(handle));
      |                                                                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 errors generated.

I'm not sure what I should cast to at this point, on FreeBSD.

If later Linux (or any other OS) requires a different code I will use #ifdefs to differentiate.

[1] https://github.com/freebsd/freebsd-src/blob/48edad2edf6eb7a539e40dad8e1f87e3fa4973fd/lib/libusb/libusb.h#L311

[droidmonkey]

Either way your static cast is incorrect in this context. Slow clap for FreeBSD for a completely divergent API with the same exact function name.

[madpilot78]

Well I don't know how and why a different API evolved in FreeBSD, but I'm trying to understand why a 64bit number on a 64bit arch cannot be cast to a pointer. The memory representation of them is the same AFAIK.

What I'm trying to do is adapt the code in keepassxc for these function to pass around pointers in place of integers. Apart fro the different type (with a different size in most cases), the API is not that much different, so the basic concept should be possible to put in practice.

[phoerious]

On Ubuntu (libusb 1.0.26), libusb_hotplug_callback_handle is typedef'ed to int. FreeBSD has an entirely different implementation of the whole library.

I think the main problem is that libusb_hotplug_callback_handle itself is not a pointer type on FreeBSD. Instead, they chose to typedef only *libusb_hotplug_callback_handle, so you have to use it with *.