From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 32022 invoked by alias); 22 Jul 2011 19:19:06 -0000 Received: (qmail 32014 invoked by uid 22791); 22 Jul 2011 19:19:05 -0000 X-SWARE-Spam-Status: No, hits=-2.5 required=5.0 tests=AWL,BAYES_00,RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from mail.codesourcery.com (HELO mail.codesourcery.com) (38.113.113.100) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 22 Jul 2011 19:18:52 +0000 Received: (qmail 9987 invoked from network); 22 Jul 2011 19:18:51 -0000 Received: from unknown (HELO scottsdale.localnet) (pedro@127.0.0.2) by mail.codesourcery.com with ESMTPA; 22 Jul 2011 19:18:51 -0000 From: Pedro Alves To: gdb-patches@sourceware.org Subject: Re: RFC: partially available registers Date: Fri, 22 Jul 2011 21:58:00 -0000 User-Agent: KMail/1.13.6 (Linux/2.6.38-8-generic; KDE/4.6.2; x86_64; ; ) Cc: Tom Tromey , Daniel Jacobowitz References: <201107222010.23822.pedro@codesourcery.com> In-Reply-To: <201107222010.23822.pedro@codesourcery.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Message-Id: <201107222018.47875.pedro@codesourcery.com> X-IsSubscribed: yes Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2011-07/txt/msg00645.txt.bz2 On Friday 22 July 2011 20:10:23, Pedro Alves wrote: > On Friday 22 July 2011 19:55:31, Tom Tromey wrote: > > >>>>> "Pedro" == Pedro Alves writes: > > > > Pedro> Ah, that's it then. I was curious to know why were the > > Pedro> upper parts of the ymm unavailable. > > > > amd64_linux_fetch_inferior_registers calls ptrace(PTRACE_GETREGSET) > > to fetch the registers. Then it passes this to amd64_supply_xsave, > > which calls i387_supply_xsave. This function then decodes the "XCR0" > > flag and determines that the upper parts were not supplied by the > > kernel; that is, we take the true branch here: > > > > if ((clear_bv & I386_XSTATE_AVX)) > > p = NULL; > > else > > p = regs; > > Ah, thanks. With a bit more context: > > case avxh: > if ((clear_bv & I386_XSTATE_AVX)) > p = NULL; > else > p = XSAVE_AVXH_ADDR (tdep, regs, regnum); > regcache_raw_supply (regcache, regnum, p); > return; > > regcache_raw_supply with p=NULL means the register > is unavailable. But before the stuff, > it meant "supply the register as 0". I seem to remember > discussing this AVX stuff with H.J., and coming to the > conclusion that what want is really 0, but maybe not. Found it: (and follow up) > gdbserver is explicitly zeroing in this case, instead > of returning unavailable, see > gdbserver/i387-fp.c:i387_xsave_to_cache. > > What does it really mean when you have an AVX > capable machine, but I386_XSTATE_AVX is clear? > > Whatever the answer, we need to fix one of native > gdb or gdbserver for consistency. -- Pedro Alves