From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: James Hogan <james.hogan@imgtec.com>,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RESEND PATCH] scsi: make struct scsi_varlen_cdb_hdr packed
Date: Thu, 11 Oct 2012 14:34:00 +0100 [thread overview]
Message-ID: <20121011143400.49f79a7f@pyramind.ukuu.org.uk> (raw)
In-Reply-To: <1349960296.2425.53.camel@dabdike.int.hansenpartnership.com>
> > The alignment is fine (the offset of the u16 is 8 bytes), but
> > unfortunately with the metag port of gcc, sizeof(struct
> > scsi_varlen_cdb_hdr) is rounded up to a 4 byte boundary (even though the
> > largest data member alignment is only 2 bytes), which is 12 bytes
> > instead of 10.
>
> That sounds to be a bug in your compiler ... it shouldn't be rounding up
> structure sizes if the structure can fit in 10 bytes. This isn't
> happening in any other architecture that I know of (otherwise we'd have
> had a reported build break).
It's not a bug for the alignment rules of the processor as far as I can
see. The architectural definition is perfectly entitled to have tail
padding in this case.
The x86 equivalent would be
struct foo {
double x;
int a;
};
which is *NOT* 12 bytes long.
It is indeed a portability bug in the scsi layer.
Alan
next prev parent reply other threads:[~2012-10-11 13:29 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-11 9:15 [RESEND PATCH] scsi: make struct scsi_varlen_cdb_hdr packed James Hogan
2012-10-11 10:01 ` Bart Van Assche
2012-10-11 11:13 ` James Hogan
2012-10-11 10:24 ` James Bottomley
2012-10-11 11:32 ` James Hogan
2012-10-11 12:58 ` James Bottomley
2012-10-11 13:34 ` Alan Cox [this message]
2012-10-11 14:10 ` James Hogan
2013-02-11 12:55 ` James Hogan
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