From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [RESEND PATCH] scsi: make struct scsi_varlen_cdb_hdr packed Date: Thu, 11 Oct 2012 13:58:16 +0100 Message-ID: <1349960296.2425.53.camel@dabdike.int.hansenpartnership.com> References: <1349946933-30314-1-git-send-email-james.hogan@imgtec.com> <1349951069.2425.44.camel@dabdike.int.hansenpartnership.com> <5076AE3B.5040509@imgtec.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5076AE3B.5040509@imgtec.com> Sender: linux-kernel-owner@vger.kernel.org To: James Hogan Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-scsi@vger.kernel.org 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