From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: James Hogan <james.hogan@imgtec.com>
Cc: 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 13:58:16 +0100 [thread overview]
Message-ID: <1349960296.2425.53.camel@dabdike.int.hansenpartnership.com> (raw)
In-Reply-To: <5076AE3B.5040509@imgtec.com>
On Thu, 2012-10-11 at 12:32 +0100, James Hogan wrote:
> On 11/10/12 11:24, James Bottomley wrote:
> > On Thu, 2012-10-11 at 10:15 +0100, James Hogan wrote:
> >> The struct scsi_varlen_cdb_hdr is expected to be exactly 10 bytes when
> >> used in struct osd_cdb_head, but it isn't marked as packed. Some
> >> architectures will round the struct size up which triggers BUILD_BUG_ON
> >> compile errors in osd_initiator.c when the outer structs are unexpected
> >> sizes. This is fixed by marking struct scsi_varlen_cdb_hdr as __packed.
> >
> > What actual problem have you encountered? The structure is {u8[8], u16}
> > which is naturally packed on every architecture I know about. I've even
> > built osd_initiator without problem on parisc, which has some of the
> > most rigid alignment rules I've seen.
>
> Hi James,
>
> 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).
James
next prev parent reply other threads:[~2012-10-11 12:58 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 [this message]
2012-10-11 13:34 ` Alan Cox
2012-10-11 14:10 ` James Hogan
2013-02-11 12:55 ` James Hogan
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1349960296.2425.53.camel@dabdike.int.hansenpartnership.com \
--to=james.bottomley@hansenpartnership.com \
--cc=james.hogan@imgtec.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-scsi@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).