linux-kernel - RE: ibmvtpm byteswapping inconsistency

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Date:   Fri, 27 Jan 2017 11:18:01 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Michal Suchánek' <msuchanek@...e.de>,
        Ashley Lai <ashleydlai@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        "Jarkko Sakkinen" <jarkko.sakkinen@...ux.intel.com>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        "tpmdd-devel@...ts.sourceforge.net" 
        <tpmdd-devel@...ts.sourceforge.net>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: ibmvtpm byteswapping inconsistency

From: Michal Suchánek
> building ibmvtpm I noticed gcc warning complaining that second word of
> struct ibmvtpm_crq in tpm_ibmvtpm_suspend is uninitialized.
> 
> The structure is defined as
> 
> struct ibmvtpm_crq {
>         u8 valid;
>         u8 msg;
>         __be16 len;
>         __be32 data;
>         __be64 reserved;
> } __attribute__((packed, aligned(8)));
> 
> initialized as
> 
>         struct ibmvtpm_crq crq;
>         u64 *buf = (u64 *) &crq;
...

Hrummfff....
What is that attribute for, seems pretty confusing and pointless to me.

I also suspect that if you want to access it as two 64bit words it
ought to be a union.

	David