From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53619) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZC1zt-0002YS-BW for qemu-devel@nongnu.org; Mon, 06 Jul 2015 04:43:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZC1zo-000103-A2 for qemu-devel@nongnu.org; Mon, 06 Jul 2015 04:43:29 -0400 Received: from mail-wi0-x234.google.com ([2a00:1450:400c:c05::234]:35796) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZC1zo-0000zM-2i for qemu-devel@nongnu.org; Mon, 06 Jul 2015 04:43:24 -0400 Received: by wiga1 with SMTP id a1so222123345wig.0 for ; Mon, 06 Jul 2015 01:43:22 -0700 (PDT) Sender: Paolo Bonzini References: <1436130533-18565-1-git-send-email-crosthwaite.peter@gmail.com> From: Paolo Bonzini Message-ID: <559A3FA6.6010806@redhat.com> Date: Mon, 6 Jul 2015 10:43:18 +0200 MIME-Version: 1.0 In-Reply-To: <1436130533-18565-1-git-send-email-crosthwaite.peter@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH] cpu_defs: Simplify CPUTLB padding logic List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Crosthwaite , qemu-devel@nongnu.org Cc: rth@twiddle.net, Peter Crosthwaite On 05/07/2015 23:08, Peter Crosthwaite wrote: > There was a complicated subtractive arithmetic for determining the > padding on the CPUTLBEntry structure. Simplify this with a union. > > Signed-off-by: Peter Crosthwaite > --- > include/exec/cpu-defs.h | 23 ++++++++++++----------- > 1 file changed, 12 insertions(+), 11 deletions(-) > > diff --git a/include/exec/cpu-defs.h b/include/exec/cpu-defs.h > index 98b9cff..5093be2 100644 > --- a/include/exec/cpu-defs.h > +++ b/include/exec/cpu-defs.h > @@ -105,17 +105,18 @@ typedef struct CPUTLBEntry { > bit 3 : indicates that the entry is invalid > bit 2..0 : zero > */ > - target_ulong addr_read; > - target_ulong addr_write; > - target_ulong addr_code; > - /* Addend to virtual address to get host address. IO accesses > - use the corresponding iotlb value. */ > - uintptr_t addend; > - /* padding to get a power of two size */ > - uint8_t dummy[(1 << CPU_TLB_ENTRY_BITS) - > - (sizeof(target_ulong) * 3 + > - ((-sizeof(target_ulong) * 3) & (sizeof(uintptr_t) - 1)) + > - sizeof(uintptr_t))]; > + union { The struct CPUTLBEntry can be changed to union CPUTLBEntry directly, with no need for the anonymous struct. > + struct { > + target_ulong addr_read; > + target_ulong addr_write; > + target_ulong addr_code; > + /* Addend to virtual address to get host address. IO accesses > + use the corresponding iotlb value. */ > + uintptr_t addend; > + }; Which compiler version started implementing anonymous structs? Or can we just add __attribute__((__aligned__(1 << CPU_TLB_ENTRY_BITS))) to the struct? I'm not sure if it affects the sizeof too, so that requires some care. Alternatively, an uint8_t padding[0] __attribute__((__aligned__(1 << CPU_TLB_ENTRY_BITS))); could maybe work? Neither is exactly the same, as they also bump the alignment of the overall struct, but they do not require anonymous structs. Paolo > + /* padding to get a power of two size */ > + uint8_t dummy[1 << CPU_TLB_ENTRY_BITS]; > + }; > } CPUTLBEntry; > > QEMU_BUILD_BUG_ON(sizeof(CPUTLBEntry) != (1 << CPU_TLB_ENTRY_BITS)); >