linux-kernel - Re: [PATCHv2 3/3] perf: add helper makefile for cross compiling libs

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Date:	Fri, 6 Nov 2015 09:09:17 +0100
From:	Rabin Vincent <rabin.vincent@...s.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 3/3] perf: add helper makefile for cross compiling libs

On Thu, Oct 29, 2015 at 10:46:49AM +0100, Ingo Molnar wrote:
> Would it be possible to add a gcc and glibc building portion as well? That would 
> make it entirely self-hosting.

Yes, but:

- Those that intend to run the built binary on a target would presumably
  already have a cross-compiler lying around which they use to build the
  rest of userspace.

- Those that don't have a cross-compiler or need a newer one can already
  very easily create one using other specialized tools such as
  crosstool-ng (see below).

> 
> Something like:
> 
>     make ARCH=arm BOOTSTRAP=1
> 
> ... would magically fetch everything needed, and (given enough Internet bandwidth 
> and a fast enough machine) build a whole cross-environment from scratch.

This is already possible using crosstool-ng.  Getting an ARM GCC 5.2
cross-compiler is as simple as:

 $ git clone git://crosstool-ng.org/crosstool-ng
 $ cd crosstool-ng
 $ ./bootstrap && ./configure --enable-local && make

 $ ./ct-ng arm-unknown-linux-gnueabi
 $ ./ct-ng build

 $ export PATH=$PATH:~/x-tools/arm-unknown-linux-gnueabi/bin/
 $ arm-unknown-linux-gnueabi-gcc --version
 arm-unknown-linux-gnueabi-gcc (crosstool-NG crosstool-ng-1.20.0-361-g85f9814) 5.2.0

> Personally I'd even use this to bootstrap kernel cross-builds.
> 
> It could also be used to cross-build to the host architecture as well: it would 
> make it easier to test perf on the latest GCC and glibc versions. (Which the host 
> distribution does not carry.)

This is also possible with crosstool-ng. You just need to build the
x86_64-unknown-linux-gnu config to get GCC 5.2 + glibc 2.22 toolchain
for an x86-64 host.
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