From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCH 02/10] xen: make GUEST_HANDLE_64() and uint64_aligned_t available everywhere Date: Tue, 25 Jun 2013 14:17:29 +0100 Message-ID: <51C99869.7080604@citrix.com> References: <1372095741-27012-1-git-send-email-david.vrabel@citrix.com> <1372095741-27012-3-git-send-email-david.vrabel@citrix.com> <51C9660D02000078000E0364@nat28.tlf.novell.com> <51C96619.8070601@citrix.com> <51C99CD802000078000E0528@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51C99CD802000078000E0528@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: Tim Deegan , Daniel Kiper , KeirFraser , Ian Campbell , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On 25/06/13 12:36, Jan Beulich wrote: >>>> On 25.06.13 at 11:42, David Vrabel wrote: >> On 25/06/13 08:42, Jan Beulich wrote: >>>>>> On 24.06.13 at 19:42, David Vrabel wrote: >>>> #define uint64_aligned_t uint64_t __attribute__((aligned(8))) >>> >>> This line is the reason why such a change is not acceptable: We >>> require the headers to not use gcc extensions outside of regions >>> guarded by dependencies on __XEN__ and/or __XEN_TOOLS__ (which >>> we know/require will always be built by gcc compatible tool chains). >> >> I did this because this is identical to what ARM is doing. >> >> I think we do what a guest handle type that is always 64 bits long. For >> x86, perhaps something like (but with a better name): >> >> #define ___DEFINE_XEN_GUEST_HANDLE(name, type) \ >> typedef struct { type *p; } \ >> __guest_handle_ ## name; \ >> #if defined(__XEN__) || (__XEN_TOOLS__) >> typedef struct { union { type *p; uint64_aligned_t q; }; } \ >> __guest_handle_64_ ## name \ >> #endif >> typedef struct { union { type *p; uint64_t q; }; } \ >> __guest_handle_new_ ## name > > The uint64_t here ... > >> #undef set_xen_guest_handle_raw >> #define set_xen_guest_handle_raw(hnd, val) \ >> do { if ( sizeof(hnd) == 8 ) *(uint64_t *)&(hnd) = 0; \ >> (hnd).p = val; \ >> } while ( 0 ) >> >> #if defined(__XEN__) || (__XEN_TOOLS__) >> #define uint64_aligned_t uint64_t __attribute__((aligned(8))) >> #define __XEN_GUEST_HANDLE_64(name) __guest_handle_64_ ## name >> #define XEN_GUEST_HANDLE_64(name) __XEN_GUEST_HANDLE_64(name) >> #endif >> >> #define __XEN_GUEST_HANDLE_NEW(name) __guest_handle_new_ ## name >> /* This must be aligned to 8 bytes with padding if necessary. */ >> #define XEN_GUEST_HANDLE_NEW(name) __XEN_GUEST_HANDLE_NEW(name) > > ... does in no way satisfy the comment here, so what's the point? The comment is unclear, sorry. /* A structure containing this type of guest handle must align the field to 8 bytes, using padding fields as necessary. */ >>> I'm afraid you'll need to find a way to do what you want in the >>> kexec interface with the traditional manual padding approach. >> >> This is fine. The kexec interface has the necessary padding and doesn't >> need the the aligned attribute. > > Not afaict, unless you meant if substituting XEN_GUEST_HANDLE_NEW() > (rather than XEN_GUEST_HANDLE()) for XEN_GUEST_HANDLE_64(). Yes. David