I mean, possible... The code I'm using to initialize the handle buffer is
this:

```C
EFI_STATUS EFIAPI UefiMain(IN EFI_HANDLE imageHandle, IN EFI_SYSTEM_TABLE*
st) {
Print(L"Attempting to find USB IO protocol\n");
UINTN numHandles = 0;
UINTN i = 0;
UINT32 UsbStatus = 0;
EFI_HANDLE* handles = NULL;
EFI_USB_IO_PROTOCOL* UsbIo = NULL;
EFI_STATUS status = st->BootServices->LocateHandleBuffer(ByProtocol,
&gEfiUsbIoProtocolGuid, NULL, &numHandles, &handles);
if (EFI_ERROR(status)) {
Print(L"Cannot find any handles for USB devices, reason: %r\n",
status);
return EFI_ABORTED;
}
Print(L"Found %d USB devices; enumerating\n", numHandles);
for (; i < numHandles; ++i) {
Print(L"Trying to open handle %d (%x)... ", i, handles[i]);
status = st->BootServices->OpenProtocol(handles[i],
&gEfiUsbIoProtocolGuid, (void**)&UsbIo, imageHandle, NULL,
EFI_OPEN_PROTOCOL_EXCLUSIVE);
if (EFI_ERROR(status)) {
Print(L"%r, skipping\n", status);
continue;
}
// ...
```
I've done my best to follow SEI secure C coding standards, like
initializing all variables, regardless of type -- e.g. initializing
pointers to 0/NULL. But I will definitely try that idea.

On 7/17/21, Andrew Fish <afish@apple.com> wrote:

On Jul 17, 2021, at 9:41 AM, Ethin Probst <harlydavidsen@gmail.com>
wrote:

Hey all,

So my UsbAudio.efi app has hit a bit of a roadblock. This code:

```C
status = st->BootServices->OpenProtocol(handles[i],
&gEfiUsbIoProtocolGuid, (void**)&UsbIo, imageHandle, NULL,
EFI_OPEN_PROTOCOL_EXCLUSIVE);
if (EFI_ERROR(status)) {
Print(L"%r, skipping\n", status);
continue;
}
```

How are you constructing handle[]? Could it have gotten stale? You could
print out the value of handle[I] on the failure.

The contents of a handle are not defined, but the current implementation
is
a pointer to an IHANDLE internal data structure in the DXE Core. If you
are
at the UEFI Shell and you `dh -v <handleNum> it will show the <handleNum>
and the value.

Shell> dh -v 98
98: 6d5CF18
….

I think you can `dh -p UsbIo’ to get the list of the UsbIo handles.

So you can poke around and see what is happening on that handle.

I guess the handle[] array could be getting corrupted? So you could check
for that?

Thanks,

Andrew Fish

Is giving me EFI_INVALID_PARAMETER and I don’t know why. I don't think
I'm violating any of its constraints, according to the specification,
and I haven't touched this code since it was written. It also happens
irregularly: sometimes it happens on the USB audio streaming device,
or if I have a device plugged in it might happen on that device, you
get the idea. But it doesn't consistently fail. Does anybody have any
idea what's going on?

--
Signed,
Ethin D. Probst

--
Signed,
Ethin D. Probst