[Buildroot] syslinux using host compiler.

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Hello,

On Thu, 24 Mar 2016 11:39:41 +0100, Gilles Chanteperdrix wrote:

> I am new to buildroot, and have been working for a couple of weeks
> with it, and everything seems to be working fine so far.

Great :-) Glad to see you on this mailing list!

> I have a question however: why is syslinux (and grub2 for that
> matter, I guess) built with the host toolchain?

For grub2, it is actually using the target compiler, see the comment in
grub2.mk:

# Grub2 is kind of special: it considers CC, LD and so on to be the
# tools to build the native tools (i.e to be executed on the build
# machine), and uses TARGET_CC, TARGET_CFLAGS, TARGET_CPPFLAGS,
# TARGET_LDFLAGS to build the bootloader itself. However, to add to
# the confusion, it also uses NM, OBJCOPY and STRIP to build the
# bootloader itself; none of these are used to build the native
# tools.

> I can understand that some tools (such as isohybrid) need to be
> executed on the host, but the final binaries are for the target. So,
> does not that call for having a separate host-syslinux and syslinux
> packages like other packages do? 

We used to have a host-syslinux package, but it was removed in commit
ac7f60d87266c30753cb45b820dc48ec834941c6 as it was no longer needed.

> The current setup only works if the host is x86.

No, because syslinux selects BR2_HOSTARCH_NEEDS_IA32_COMPILER, which
ensures you have a working x86 32-bits compiler on your host machine. If
you don't, then Buildroot will not even start the build.

The reason why we're using the host compiler rather than the target
compiler is because syslinux must be built as 32-bits x86 code, even if
your target system is x86_64.

> I am using an x86_64 toolchain generated with ct-ng, did not enable
> multilib, and syslinux seems to have no problem compiling with that
> toolchain, which seems normal, since the boot code should not be
> using the libc anyway.

Are you sure you're using this target compiler to build syslinux, and
not your host compiler? Back in 2014, when commit
09e7b4c89159a3e48f463b0a22e649c4fc12f4b3 was done, it wouldn't build
with a x86-64 only compiler.

If that actually works, then patches are welcome. But in this case, we
will indeed probably need separate host-syslinux and syslinux packages,
as you suggested.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com