From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40929) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZC4wv-0008JM-Fh for qemu-devel@nongnu.org; Mon, 06 Jul 2015 07:52:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZC4ws-0007e7-3Y for qemu-devel@nongnu.org; Mon, 06 Jul 2015 07:52:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55638) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZC4wr-0007dv-V7 for qemu-devel@nongnu.org; Mon, 06 Jul 2015 07:52:34 -0400 References: <1436130533-18565-1-git-send-email-crosthwaite.peter@gmail.com> <559A3FA6.6010806@redhat.com> <559A69A7.9030008@twiddle.net> From: Paolo Bonzini Message-ID: <559A6BFD.6030409@redhat.com> Date: Mon, 6 Jul 2015 13:52:29 +0200 MIME-Version: 1.0 In-Reply-To: <559A69A7.9030008@twiddle.net> Content-Type: text/plain; charset=windows-1252 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: Richard Henderson , Peter Crosthwaite , qemu-devel@nongnu.org Cc: Peter Crosthwaite On 06/07/2015 13:42, Richard Henderson wrote: > 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. Of course. :-( With no need for the anonymous _union_. *blush*. >> Which compiler version started implementing anonymous structs? > > A long long time ago -- gcc 2 era. Great. I now remember that the recent feature is anonymous tagged structs, coming from the Plan 9 compiler. Paolo >> 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~