Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754378AbbKXODi (ORCPT ); Tue, 24 Nov 2015 09:03:38 -0500 Received: from unicorn.mansr.com ([81.2.72.234]:38465 "EHLO unicorn.mansr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752645AbbKXODh convert rfc822-to-8bit (ORCPT ); Tue, 24 Nov 2015 09:03:37 -0500 From: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= To: Russell King - ARM Linux Cc: Arnd Bergmann , linux-arm-kernel@lists.infradead.org, Stephen Boyd , Nicolas Pitre , Peter Maydell , "linux-arm-msm\@vger.kernel.org" , Daniel Lezcano , lkml - Kernel Mailing List , Steven Rostedt , Christopher Covington Subject: Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions References: <1448068997-26631-1-git-send-email-sboyd@codeaurora.org> <20151124001306.GI19156@codeaurora.org> <20151124085349.GQ19156@codeaurora.org> <4485320.CGMJdfZLya@wuerfel> <20151124104225.GA8644@n2100.arm.linux.org.uk> <20151124122308.GB8644@n2100.arm.linux.org.uk> <20151124140047.GC8644@n2100.arm.linux.org.uk> Date: Tue, 24 Nov 2015 14:03:27 +0000 In-Reply-To: <20151124140047.GC8644@n2100.arm.linux.org.uk> (Russell King's message of "Tue, 24 Nov 2015 14:00:47 +0000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2407 Lines: 55 Russell King - ARM Linux writes: > On Tue, Nov 24, 2015 at 12:29:06PM +0000, M?ns Rullg?rd wrote: >> Russell King - ARM Linux writes: >> >> > On Tue, Nov 24, 2015 at 12:10:02PM +0000, M?ns Rullg?rd wrote: >> >> Russell King - ARM Linux writes: >> >> >> >> > On Tue, Nov 24, 2015 at 11:38:53AM +0100, Arnd Bergmann wrote: >> >> >> I suggested using -mcpu=cortex-a15 because there are old gcc versions >> >> >> that don't know about -march=armv7ve or -march=armv7-a+idiv yet, but >> >> >> that do understand -mcpu=cortex-a15. >> >> > >> >> > That's not all. The bigger problem is that there are toolchains out >> >> > there which accept these options, but do _not_ support IDIV in either >> >> > ARM or Thumb mode. I'm afraid that makes it impossible to add this >> >> > feature to the mainline kernel in this form: we need to run a test >> >> > build to check that -march=armv7ve or what-not really does work >> >> > through both GCC and GAS. >> >> >> >> If the compiler accepts the option but doesn't actually emit any div >> >> instructions, is there any real harm? >> > >> > That's not what I've found. I've found that asking the assembler >> > to accept idiv instructions appears to be ignored, which is something >> > completely different. >> > >> > Further to this, what it comes down to is the stupid idea that the >> > compiler should embed .arch / .cpu in the assembly output, which has >> > the effect of overriding the command line arguments given to it via >> > -Wa. So, giving -Wa,-mcpu=cortex-a15 is a total no-op, because the >> > first thing in the assembly output is: >> > >> > .arch armv7-a >> > >> > which kills off any attempt to set the assembly level ISA from the >> > command line. >> >> Oh, you mean the compiler knows about the instructions but the assembler >> doesn't or isn't passed the right options. It's infuriating when that >> happens. > > No, that isn't what I meant. Then what do you mean? The compiler either emits the instructions or it doesn't. If it doesn't, what the assembler accepts is irrelevant. -- M?ns Rullg?rd mans@mansr.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/