From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754716AbbFWL4m (ORCPT ); Tue, 23 Jun 2015 07:56:42 -0400 Received: from ozlabs.org ([103.22.144.67]:57424 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754576AbbFWL4f (ORCPT ); Tue, 23 Jun 2015 07:56:35 -0400 From: Rusty Russell To: Fabian Frederick , linux-kernel@vger.kernel.org Cc: Julia Lawall , Fabian Frederick , lguest@lists.ozlabs.org Subject: Re: [RFC 1/1 linux-next] tools/lguest: update variables to avoid setreg(eax, eax) In-Reply-To: <1434486430-14003-1-git-send-email-fabf@skynet.be> References: <1434486430-14003-1-git-send-email-fabf@skynet.be> User-Agent: Notmuch/0.17 (http://notmuchmail.org) Emacs/24.4.1 (x86_64-pc-linux-gnu) Date: Tue, 23 Jun 2015 21:15:09 +0930 Message-ID: <87ioaesl6i.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Fabian Frederick writes: > eax is used for offset calculation but is also a local > variable used to store register value. Well, it's the value we're going to put back in eax. And it came from eax. Renaming val to def_val is weird, since it's not the default. You can tell it's set in various places. I don't think this patch adds clarity. What are you trying to do? Thanks, Rusty. > tools/lguest/lguest.c | 26 +++++++++++++------------- > 1 file changed, 13 insertions(+), 13 deletions(-) > > diff --git a/tools/lguest/lguest.c b/tools/lguest/lguest.c > index e440524..d466c79 100644 > --- a/tools/lguest/lguest.c > +++ b/tools/lguest/lguest.c > @@ -1611,12 +1611,12 @@ static void emulate_insn(const u8 insn[]) > { > unsigned long args[] = { LHREQ_TRAP, 13 }; > unsigned int insnlen = 0, in = 0, small_operand = 0, byte_access; > - unsigned int eax, port, mask; > + unsigned int val, port, mask; > /* > * Default is to return all-ones on IO port reads, which traditionally > * means "there's nothing there". > */ > - u32 val = 0xFFFFFFFF; > + u32 defval = 0xFFFFFFFF; > > /* > * This must be the Guest kernel trying to do something, not userspace! > @@ -1692,29 +1692,29 @@ static void emulate_insn(const u8 insn[]) > * If it was an "IN" instruction, they expect the result to be read > * into %eax, so we change %eax. > */ > - eax = getreg(eax); > + val = getreg(eax); > > if (in) { > /* This is the PS/2 keyboard status; 1 means ready for output */ > if (port == 0x64) > - val = 1; > + defval = 1; > else if (is_pci_addr_port(port)) > - pci_addr_ioread(port, mask, &val); > + pci_addr_ioread(port, mask, &defval); > else if (is_pci_data_port(port)) > - pci_data_ioread(port, mask, &val); > + pci_data_ioread(port, mask, &defval); > > /* Clear the bits we're about to read */ > - eax &= ~mask; > - /* Copy bits in from val. */ > - eax |= val & mask; > + val &= ~mask; > + /* Copy bits in from defval. */ > + val |= defval & mask; > /* Now update the register. */ > - setreg(eax, eax); > + setreg(eax, val); > } else { > if (is_pci_addr_port(port)) { > - if (!pci_addr_iowrite(port, mask, eax)) > + if (!pci_addr_iowrite(port, mask, val)) > goto bad_io; > } else if (is_pci_data_port(port)) { > - if (!pci_data_iowrite(port, mask, eax)) > + if (!pci_data_iowrite(port, mask, val)) > goto bad_io; > } > /* There are many other ports, eg. CMOS clock, serial > @@ -1722,7 +1722,7 @@ static void emulate_insn(const u8 insn[]) > } > > verbose("IO %s of %x to %u: %#08x\n", > - in ? "IN" : "OUT", mask, port, eax); > + in ? "IN" : "OUT", mask, port, val); > skip_insn: > /* Finally, we've "done" the instruction, so move past it. */ > setreg(eip, getreg(eip) + insnlen); > -- > 2.4.2