From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37996) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZC4nX-0001pS-GD for qemu-devel@nongnu.org; Mon, 06 Jul 2015 07:42:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZC4nU-0002kJ-Aw for qemu-devel@nongnu.org; Mon, 06 Jul 2015 07:42:55 -0400 Received: from mail-qg0-x235.google.com ([2607:f8b0:400d:c04::235]:36004) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZC4nU-0002jw-4x for qemu-devel@nongnu.org; Mon, 06 Jul 2015 07:42:52 -0400 Received: by qgeg89 with SMTP id g89so67386839qge.3 for ; Mon, 06 Jul 2015 04:42:50 -0700 (PDT) Sender: Richard Henderson References: <1436130533-18565-1-git-send-email-crosthwaite.peter@gmail.com> <559A3FA6.6010806@redhat.com> From: Richard Henderson Message-ID: <559A69A7.9030008@twiddle.net> Date: Mon, 6 Jul 2015 12:42:31 +0100 MIME-Version: 1.0 In-Reply-To: <559A3FA6.6010806@redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] cpu_defs: Simplify CPUTLB padding logic List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , Peter Crosthwaite , qemu-devel@nongnu.org Cc: Peter Crosthwaite On 07/06/2015 09:43 AM, Paolo Bonzini wrote: > > > 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. Um, no it can't. That would put all of the members at the same address. > Which compiler version started implementing anonymous structs? A long long time ago -- gcc 2 era. > Or can we just add > > __attribute__((__aligned__(1 << CPU_TLB_ENTRY_BITS))) The structure isn't currently aligned, and it needn't be. We only need the size to be a power of two for the addressing. r~