Build LSK 3.14 kernel with android-toolchain

[arnd@arndb.de (Arnd Bergmann)]

On Tuesday 02 December 2014 17:39:21 Jisheng Zhang wrote:
> 
> On Tue, 2 Dec 2014 01:04:54 -0800
> Shawn Guo <shawn.guo@linaro.org> wrote:
> 
> > + LAKML and more people.
> > 
> > On Mon, Dec 01, 2014 at 05:38:38PM +0100, Arnd Bergmann wrote:
> > > On Monday 01 December 2014 16:32:21 Shawn Guo wrote:
> > > > Is it a valid or supported use case to build LSK 3.14 kernel with
> > > > android-toolchain?  I can build a LSK 3.14 kernel with Linux toolchain
> > > > gcc-linaro-arm-none-eabi-4.9-2014.09, which boots fine on my board.
> > > > When I build the same kernel with
> > > > android-toolchain-eabi-4.9-2014.09-x86, the kernel can be built out
> > > > successfully, but it fails to boot on the board at very early stage
> > > > with only uncompressing message shown up like below.
> > > > 
> > > > Uncompressing Linux... done, booting the kernel.
> > > > 
> > > > And it's not a LSK 3.14 specific problem, I tried to build mainline
> > > > 3.10, 3.14 and 3.18-rc4 with the android-toolchain, and they all
> > > > failed to boot.
> > > > 
> > > > I need some help to understand if it's a valid use case at all, before
> > > > I try to looking into the problem.
> > > 
> > > I would expect it to work, it's probably a good idea to find out
> > > why it doesn't. For all I know 'arm-none-eabi' is actually /not/
> > > supported for building the kernel, since that doesn't use the Linux
> > > Linux variant of eabi, while 'arm-*-linux-gnueabi' or
> > > 'arm-*-linux-gnueabihf' is the default for Linux these days and
> > > 'arm-*-linux-android' should be compatible with that.
> > 
> > Okay.  Thanks for the info.  It seems that I should download
> > gcc-linaro-arm-linux-gnueabihf-4.9-2014.09 for comparison testing then.
> > Actually, in the very first testing I used arm-linux-gnueabi-gcc 4.7.3
> > shipped with Ubuntu 14.04.
> > 
> > > What is the
> > > exact target triplet you use in those two cases?
> > 
> > They are arm-none-eabi and arm-linux-androideabi.  And I also replaced
> > the first toolchain with arm-linux-gnueabi one, and got the same result.

Ok, so they are really all different.

> > > 
> > > A few things you could try:
> > > 
> > > - boot it in qemu using the vexpress or virt platform code, see if
> > >   the symptom is the same. If it is, attach gdb to the qemu gdbstub
> > >   to look at the contents of the _log_buf.
> > > 
> > > - Maybe debug_ll crashes, try disabling that
> > > 
> > > - Maybe debug_ll is disabled already, try enabling it to see if you
> > >   get more output.
> > 
> > I tracked it a little bit with debug_ll routine printch() and found it
> > dies at the first pr_info() call in arch/arm/kernel/setup.c:
> > 
> >       pr_info("Booting Linux on physical CPU 0x%x\n", mpidr);
> > 
> > And I spent some time to find out that the issue was introduced by
> > commit dad5451a322b (ARM: 7605/1: vmlinux.lds: Move .notes section
> > next to the rodata) since v3.8 release.  Reverting the commit helps me
> > to get a booting kernel that is built by arm-linux-androideabi
> > toolchain.  But I do not have the knowledge to understand what is
> > happening.
> > 
> 
> From my experience in last several years
> 
> 1. the arm-linux-androideabi- toolchain sets some options by default, PIC for
> example, even -mno-android can't disable all the side effects per my test.

Yes, that's definitely possible. Any idea how the android folks build their
kernel?

> 2. the arm-linux-eandroideabi- toolchain use gold for linker by default. Maybe
> gold can't understand vmlinux.lds correctly?

That would be very easy to test, just set LD=${CROSS_COMPILE}ld.bfd on the
command line and rebuild. In my testing, I've encountered a number of different
bugs in both ld.bfd and ld.gold that prevent you from building the kernel.

	Arnd