Re: [PATCH v2] deb-pkg: generate correct build dependencies

From: Ben Hutchings <ben@decadent.org.uk>
To: Masahiro Yamada <yamada.masahiro@socionext.com>,
	Riku Voipio <riku.voipio@linaro.org>
Cc: Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
	debian-kernel <debian-kernel@lists.debian.org>
Subject: Re: [PATCH v2] deb-pkg: generate correct build dependencies
Date: Mon, 18 Feb 2019 17:54:04 +0000	[thread overview]
Message-ID: <ab49b0582ef12b14b1a68877263b81813e2492a2.camel@decadent.org.uk> (raw)
In-Reply-To: <CAK7LNASiyMiCB2Ko0_aWOhB_3t6FEVhQ1xpnn-NQ=yV0X11SMg@mail.gmail.com>

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On Tue, 2019-02-19 at 02:05 +0900, Masahiro Yamada wrote:
[...]
> "make allnoconfig; make bindeb-pkg"
> failed on Ubuntu 16.04, but succeeded on Ubuntu 18.04
> 
> I am puzzled...
[...]
> dpkg-buildpackage: host architecture i386
>  dpkg-source --before-build linux
> dpkg-checkbuilddeps: error: Unmet build dependencies: flex
> dpkg-buildpackage: warning: build dependencies/conflicts unsatisfied; aborting
> dpkg-buildpackage: warning: (Use -d flag to override.)
> scripts/package/Makefile:78: recipe for target 'bindeb-pkg' failed
> make[1]: *** [bindeb-pkg] Error 3
> Makefile:1390: recipe for target 'bindeb-pkg' failed
> make: *** [bindeb-pkg] Error 2
> 
> 
> The docker file I used is below.
> 
> If I change "FROM ubuntu:16.04" to "FROM ubuntu:18.04",
> it goes well.
[...]

For a cross-build, some build-dependencies may need to belong to the
host architecture (what the package will run on) while others do not. 
In general, they must do one of:

(a) Belong to the host architecture
(b) Belong to any architecture, and include "Multi-Arch: foreign" in
    their own metadata
(c) Belong to an architecture specified in the Build-Depends field

We normally want (b) for tools like flex.  But flex is (I assume)
missing the Multi-Arch field in Ubuntu 16.04, as it used to in Debian.

The way we dealt with this in Debian before flex was fixed was (c): use
"flex:native".  But for reasons I don't understand that *isn't*
compatible with (b), so to be compatible with both old and new versions
of flex you should build-depend on:

   flex | flex:native

Ben.

-- 
Ben Hutchings
The obvious mathematical breakthrough [to break modern encryption]
would be development of an easy way to factor large prime numbers.
                                                           - Bill Gates

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