Re: LocateHandle for gEfiShellProtocolGuid is failing in my application

[Andrew Fish <afish@apple.com>]

> On Dec 20, 2016, at 11:32 PM, GN Keshava <keshava.gn@gmail.com> wrote:
> 
> Hi,
> 
> I'm developing a shell application. A call to LocateHandle for
> gEfiShellProtocolGuid is failing with Status 0x0E.
> 
> Below is my code. Please let me know what I'm doing wrong.
> 

Assuming this is your entire code fragment you are passing 2 uninitialized values 

If you want to probe the size you need to:
BufferSize = 0;

> Status = gBS->LocateHandle(ByProtocol, &gEfiShellProtocolGuid, NULL,
> &BufferSize, Buffer); // Get BufferSize
> if (EFI_ERROR(Status))

Per the spec you would expect to get Status = EFI_BUFFER_TOO_SMALL if you need to grow the size. You should only allocate the buffer and retry if you get EFI_BUFFER_TOO_SMALL. 

You don't handle the case of  EFI_NOT_FOUND.

FYI the error codes are defined in the UEFI Spec and exist here in the code:
https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Base.h <https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Base.h>



///
/// The buffer was not large enough to hold the requested data.
/// The required buffer size is returned in the appropriate
/// parameter when this error occurs.
///
#define RETURN_BUFFER_TOO_SMALL      ENCODE_ERROR (5)


...

///
/// The item was not found.
///
#define RETURN_NOT_FOUND             ENCODE_ERROR (14)


#define ENCODE_ERROR(StatusCode)     ((RETURN_STATUS)(MAX_BIT | (StatusCode)))


MAX_BIT is going to be defined as BIT63 or BIT31 depending on the CPU architecture you are using. 


> Print(L"LocateHandle Status 0x%x\n",Status);
> 
> Status = gBS->AllocatePool(EfiBootServicesData, BufferSize,
> (void**)&Buffer);
> if (EFI_ERROR(Status))
> Print(L"AllocatePool Status 0x%x\n",Status);
> 

I mentioned in the other mail that you can use %r to get a string for the error.

Thanks,

Andrew Fish


> Status = gBS->LocateHandle(ByProtocol, &gEfiShellProtocolGuid, NULL,
> &BufferSize, Buffer);
> if (EFI_ERROR(Status))
> Print(L"LocateHandle Status 0x%x\n",Status);
> 
> All calls failing with Status being 0x0E. Please help me to solve this. Is
> there any special requirement for using this protocol?
> 
> Thanks.
> Regards,
> Keshava
> ___________________________________