From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailrelay4-1.pub.mailoutpod2-cph3.one.com (mailrelay4-1.pub.mailoutpod2-cph3.one.com [46.30.211.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3FD9914A98 for ; Sun, 24 Mar 2024 08:54:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=46.30.211.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711270446; cv=none; b=hOAlIQL+YcT2LX4Vk1HHfVhBr82+Xq8Z7FzarInMcvOjDRVSiHqJziK5HWtvfHp0F81RadkmgqkMfu2qxrJgtPHQhYsJFVAuI1/VP5HGEMffXEKIHDk1pTjqWKcAZxcBHyA2EZGpD9ePjZXvlwb3UeZdeTA+gs5bt2/SJS2PO84= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711270446; c=relaxed/simple; bh=hs4jUUCt48qL2QwMZOjgM2vlRF2cE3r2RtwVXG9sQyg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jfOV/Ms9DrWTNZPzeI0QKhDjrsNPNYS6pPxkA17+Um5jNvpiiu2y3bfFLGz7X+4UYhuo2ApVpRhAzR2uSXiGHMr/wGPVY6miLGpaXjTEemSY26cxY5zeI8lpezTqp9RECBTRyReOnDuTr3Go+yUjIhgWPs6y0gTRieleyzNa7Ng= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ravnborg.org; spf=none smtp.mailfrom=ravnborg.org; dkim=pass (2048-bit key) header.d=ravnborg.org header.i=@ravnborg.org header.b=VYbU9FNj; dkim=permerror (0-bit key) header.d=ravnborg.org header.i=@ravnborg.org header.b=AiaAJIoT; arc=none smtp.client-ip=46.30.211.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ravnborg.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ravnborg.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ravnborg.org header.i=@ravnborg.org header.b="VYbU9FNj"; dkim=permerror (0-bit key) header.d=ravnborg.org header.i=@ravnborg.org header.b="AiaAJIoT" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ravnborg.org; s=rsa2; h=in-reply-to:content-type:mime-version:references:message-id:subject:cc:to: from:date:from; bh=ilBS90by6SCxKHHjd4xnZkERRnipn9y3PlIFePRKJHc=; b=VYbU9FNj6VSnUa2rpdrDNmnElZTZ+9DJbvbTituVggOzor800hcuK48psEVekaK2y8Q7djF5izlCF ki1VaRD3Zfw9vaRUzfhaPiNqVmQWKnCd+HLtbi3UbdS1TcINjbRJhVtMl86KeSXwOi6VadAIP3Tv7s WPbrRFBmXKo9WBzYFaMMl7rymi4iwtgaoNrsNbnRZFUKz2FNSuyGsn0QLoIFHx3bz3wV/keTT5/9d2 MQ2mm+lNxJWTHn7t5gf5jTa+KejQs2l42hl05hpyixeYKB9V1ol3uwF2K3HfLP0ruwZ+G0wOPwVEYC HgTsU6gHSocO8S+c872Nsr55kTyfOtA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=ravnborg.org; s=ed2; h=in-reply-to:content-type:mime-version:references:message-id:subject:cc:to: from:date:from; bh=ilBS90by6SCxKHHjd4xnZkERRnipn9y3PlIFePRKJHc=; b=AiaAJIoTJmv6xZNJHngHZvUJNkec2JzXAnJzlxV6mJvUpkPadMUGw4GC4tjb0dkT9DpSsTWXEqRkg 7tBj58IBg== X-HalOne-ID: 09b88606-e9bc-11ee-a6fe-31e85a7fa845 Received: from ravnborg.org (2-105-2-98-cable.dk.customer.tdc.net [2.105.2.98]) by mailrelay4.pub.mailoutpod2-cph3.one.com (Halon) with ESMTPSA id 09b88606-e9bc-11ee-a6fe-31e85a7fa845; Sun, 24 Mar 2024 08:53:55 +0000 (UTC) Date: Sun, 24 Mar 2024 09:53:53 +0100 From: Sam Ravnborg To: Koakuma Cc: "sparclinux@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "davem@davemloft.net" , "ndesaulniers@google.com" , "arnd@arndb.de" Subject: Re: [sparc] Use of -fcall-used-* flags in Makefile? Message-ID: <20240324085353.GA1382477@ravnborg.org> References: <20240319221615.GA379167@ravnborg.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi Koakuma. On Sat, Mar 23, 2024 at 04:37:27PM +0000, Koakuma wrote: > Hello Sam, > > Sam Ravnborg wrote: > > > Hi Koakuma, > > Looking at https://github.com/gcc-mirror/gcc/blob/master/gcc/config/sparc/sparc.h > > I read that: > > > > On v9 systems: > > g1,g5 are free to use as temporaries, and are free to use between calls > > ... > > g6-g7 are reserved for the operating system (or application in > > embedded case). > > > > Based on the above I would assume gcc do not change behaviour with or > > without -fcall-used-g7. > > [...] > > For sparc32 the above file says: > > > > g5 through g7 are reserved for the operating system. > > > > So again - it looks like -fcall-used-g5 -fcall-used-g7 should have no > > effect here and verification on a real target would be nice. > > > > Sam > > >From my understanding (and looking at the codegen results) those flags > forces GCC to treat the named register as volatile, despite what the ABI > says. However, I also believe that removing them wouldn't be harmful? > > To quote my reasoning in the LLVM tracker: > > omitting the flags shouldn't be harmful either - compilers will now > > simply refuse to touch them, and any assembly code that happens > > to touch them would still work like usual (because Linux' conventions > > already treats them as volatile anyway). > > But I am not entirely sure about it, that is why it'd be great if there's > some explaination on why those flags were added in the first place. > > > I do not have a sparc64 system at my hands - and for this qemu may not > > cut it. But it would be super if someone with a working sparc64 target > > could verify if the kernel could be built and works without > > -fcall-used-g7. > > I am currently running a build with those flags taken out on a T5120, > and the kernel seems to be running okay for what I do (LLVM development), > but I don't know if there are more comprehensive test suite for me > to try on. I tried to build a sparc32 kernel with the two -fcall-used-g5 -fcall-used-g7 flags dropped. Everything worked for me in qemu - but then I only booted to a prompt and browsed around a little. >From your explanation and our limited testing it seems likely the flags can be dropped, but I cannot say for sure. Unless others chime in maybe try to send in patches to drop the flags from sparc32 and sparc64 and see how it goes. Sam