From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.domeneshop.no (smtp.domeneshop.no [194.63.252.55]) (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 ABD1A18E0E; Thu, 1 Aug 2024 07:04:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=194.63.252.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722495892; cv=none; b=AtH9LZTwETB2kh8IClqPM2XLBidmn9bT3UGmRnB9cdubiddB5df0FytHBpMd57pvWWOdsJGEdE3lhtHyGJ2PcyPll1YqqmiEvSrT23lo7OfYw5y3irMyY+k4tY2lln3XwTCMJtNNED2HXzuthHsZ78crue0MMi5BK9b8pboDt7w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722495892; c=relaxed/simple; bh=BaVlJRN/6hPJp9l19L8ToU280ekcfomw2D+4NZlM194=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qT8/MEbysTMb0M5/qScjCKM8/3tGZzqX60lYSzFySv5SV8BQBPG8AkQI14zJvcidmIbiIOk4y2Utz7TNItURD6xHfy11qufTeZsEA52TrvJdDMNYSFfuIFYKeSaQf31gziAyQpQcf/tjO2xB3aK8GQDpt2R2XObjdL/avq2xfmY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=fjasle.eu; spf=pass smtp.mailfrom=fjasle.eu; dkim=pass (2048-bit key) header.d=fjasle.eu header.i=@fjasle.eu header.b=NGW1LMRT; arc=none smtp.client-ip=194.63.252.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=fjasle.eu Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=fjasle.eu Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=fjasle.eu header.i=@fjasle.eu header.b="NGW1LMRT" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=fjasle.eu; s=ds202307; h=In-Reply-To:Content-Transfer-Encoding:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:From:Sender:Reply-To:Subject: Date:Message-ID:To:Cc:MIME-Version:Content-Type:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=61UZKpDQzaF9GUCZxf/tmbLRyDF/Ip+EC4Mbam9rse8=; b=NGW1LMRTNP+8JbP8ljr89Daoqp FeZQCOKnWc74tPRBET6YrJYarkgVly2uJckeL6nSiN+LMPUDXy4TLjDep2JtZHERzhxSL1Kzw84fd s9zEFZJDdb2pEbT8UwZODl1Q45OKMiBRx0SxwcOe5jEN6tEyYCIG3fj0lT7Mx5f9Pzb2uGlRtuSxy Q2reyXVpy1uLnU/DzHhni0YGOvw5r5P1VaDj3OeFsDysmqcowBoaZ0QDhGiLntjlI7P3DIX4lBa3Q RXEyO2MbACcKAX8FBOHKDXzKk5gbGYU/FoRwlNLHHleouzZc1s4KbTfXKFFt+Km1jJislEO3DFuzE 69o5xB/g==; Received: from [2001:9e8:9df:2b01:3235:adff:fed0:37e6] (port=51948 helo=lindesnes.fjasle.eu) by smtp.domeneshop.no with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1sZPra-00AnRX-R9; Thu, 01 Aug 2024 09:04:39 +0200 Date: Thu, 1 Aug 2024 09:04:33 +0200 From: Nicolas Schier To: Masahiro Yamada Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Kees Cook , Nathan Chancellor , Ben Hutchings Subject: Re: [PATCH 4/4] kbuild: cross-compile linux-headers package when possible Message-ID: <20240801-peculiar-soft-oarfish-acc596@lindesnes> References: <20240727074526.1771247-1-masahiroy@kernel.org> <20240727074526.1771247-5-masahiroy@kernel.org> <20240731-soft-kittiwake-of-election-a1dfa0@lindesnes> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Aug 01, 2024 at 11:37:30AM +0900, Masahiro Yamada wrote: > On Thu, Aug 1, 2024 at 6:10 AM Nicolas Schier wrote: > > > > On Sat, Jul 27, 2024 at 04:42:04PM +0900, Masahiro Yamada wrote: > > > A long standing issue in the upstream kernel packaging is that the > > > linux-headers package is not cross-compiled. > > > > > > For example, you can cross-build Debian packages for arm64 by running > > > the following command: > > > > > > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- bindeb-pkg > > > > > > However, the generated linux-headers-*_arm64.deb is useless because the > > > host programs in it were built for your build machine architecture > > > (likely x86), not arm64. > > > > > > The Debian kernel maintains its own Makefiles to cross-compile host > > > tools without relying on Kbuild. [1] > > > > > > Instead of adding such full custom Makefiles, this commit adds a small > > > piece of code to cross-compile host programs located under the scripts/ > > > directory. > > > > > > A straightforward solution is to pass HOSTCC=${CROSS_COMPILE}gcc, but it > > > would also cross-compile scripts/basic/fixdep, which needs to be native > > > to process the if_changed_dep macro. (This approach may work under some > > > circumstances; you can execute foreign architecture programs with the > > > help of binfmt_misc because Debian systems enable CONFIG_BINFMT_MISC, > > > but it would require installing QEMU and libc for that architecture.) > > > > > > A trick is to use the external module build (KBUILD_EXTMOD=), which > > > does not rebuild scripts/basic/fixdep. ${CC} needs to be able to link > > > userspace programs (CONFIG_CC_CAN_LINK=y). > > > > > > There are known limitations: > > > > > > - GCC plugins > > > > > > It would possible to rebuild GCC plugins for the target architecture > > > by passing HOSTCXX=${CROSS_COMPILE}g++ with necessary packages > > > installed, but gcc on the installed system emits > > > "cc1: error: incompatible gcc/plugin versions". I did not find a > > > solution for this because 'gcc' on a foreign architecture is a > > > different compiler after all. > > > > > > - objtool and resolve_btfids > > > > > > These are built by the tools build system. They are not covered by > > > the current solution. > > > > > > I only tested this with Debian, but it should work for other package > > > systems as well. > > > > > > [1]: https://salsa.debian.org/kernel-team/linux/-/blob/debian/6.9.9-1/debian/rules.real#L586 > > > > > > Signed-off-by: Masahiro Yamada > > > --- > > > > > > scripts/package/install-extmod-build | 34 ++++++++++++++++++++++++++++ > > > 1 file changed, 34 insertions(+) > > > > > > diff --git a/scripts/package/install-extmod-build b/scripts/package/install-extmod-build > > > index cc335945dfbc..0b56d3d7b48f 100755 > > > --- a/scripts/package/install-extmod-build > > > +++ b/scripts/package/install-extmod-build > > > @@ -43,4 +43,38 @@ mkdir -p "${destdir}" > > > fi > > > } | tar -c -f - -T - | tar -xf - -C "${destdir}" > > > > > > +# When ${CC} and ${HOSTCC} differ, we are likely cross-compiling. Rebuild host > > > +# programs using ${CC}. This assumes CC=${CROSS_COMPILE}gcc, which is usually > > > +# the case for package building. It does not cross-compile when CC=clang. > > > +# > > > +# This caters to host programs that participate in Kbuild. objtool and > > > +# resolve_btfids are out of scope. > > > > Just for clarification: Why do you call both "out of scope" here? > > Because they're not being built by kbuild, or because they will never be > > needed for building oot kmods? > > > I meant the former. > > > Debian applies a tricky patch to the tools build system > in order to cross-compile objtool: > > https://salsa.debian.org/kernel-team/linux/-/blob/debian/6.9.9-1/debian/patches/debian/fixdep-allow-overriding-hostcc-and-hostld.patch > > It is not an elegant solution, though. > > > I still believe the right thing to do is > converting Makefiles for objtool and resolve_btfids into Kbuild style. > > > objtool and resolve_btfids are necessary for building external modules, > when CONFIG_OBJTOOL=y and CONFIG_DEBUG_INFO_BTF=y, respectively. > If these comments are confusing, I can delete them. I think it's good to mention that cross-built linux-headers package is still broken for CONFIG_OBJTOOL=y and CONFIG_DEBUG_INFO_BTF=y. I think I'd add a sentence to the commit message and keep the comment here as it is. Kind regards, Nicolas