[Buildroot] [PATCH] m68k: add support for coldfire with qemu config

Fri Apr 29 16:27:32 UTC 2016

Hi Thomas,
Thomas Petazzoni wrote,

Thanks for the detailed feedback.

> Hello,
> 
> Cool, some coldfire stuff!
> 
> On Wed, 27 Apr 2016 19:36:55 +0200, Waldemar Brodkorb wrote:
> > There are four different possibilities for m68k
> > architecture and cpu support:
> > m68k with MMU f.e m68040
> > m68k without MMU f.e. m68020 (without coprocessor)
> > coldfire without MMU f.e. mcf5208
> > coldfire with MMU f.e. mcf5475
> > 
> > This adds just support for mcf5208.
> > 
> > We need to enable multilib to gcc build to support coldfire.
> 
> Can you give more details as to why multilib is needed? That's a fairly
> significant change, so we shouldn't do it lightly.

I have done more testing, it seems not to be required :)

> Is this minimal Busybox config significantly different than the one in
> board/stmicroelectronics/busybox-minimal.config ? If not, then maybe
> it's time to move it to package/busybox/.

It is the same. Maybe networking stuff could be enabled later,
because with a minor kernel patch you can enable networking
in qemu-system-m68k. 

> This whole thing should be split into more patches. At least split the:
> 
>  1/ Architecture + toolchain support
>  2/ Defconfig stuff
>  3/ Addition of the Busybox configuration in package/busybox

Will be done in the next patch series.

> >  config BR2_m68k_68040
> >  	bool "68040"
> > +	select BR2_m68k_m68k
> > +	select BR2_ARCH_HAS_MMU_OPTIONAL
> 
> We used to select BR2_ARCH_HAS_MMU_MANDATORY. Are you sure you can
> effectively run Linux on a 68040 with the MMU disabled? If you're not
> sure, just keep BR2_ARCH_HAS_MMU_MANDATORY.

Okay.

> > +config BR2_m68k_cf5208
> > +	bool "5208"
> > +	select BR2_m68k_cf
> > +	select BR2_SOFT_FLOAT
> >  
> >  endchoice
> >  
> >  config BR2_GCC_TARGET_CPU
> >  	default "68040"		if BR2_m68k_68040
> > +	default "5208"		if BR2_m68k_cf5208
> 
> You also want to add:
> 
> config BR2_GCC_TARGET_ARCH
> 	default "m68k" if BR2_m68k_m68k
> 	default "cf" if BR2_m68k_cf
> 
> this will allow to remove some stuff later on.
> 
> > +rm -f ${TARGET_DIR}/etc/init.d/S20urandom
> 
> Why ?

No reason. It was there because I tried to get the thing booting to
the command line and iteratively disabled or add some stuff to make
it work. :)

> > +# mdev does not work correctly
> > +BR2_ROOTFS_DEVICE_CREATION_STATIC=y
> 
> The default is not to use mdev, but to use devtmpfs only. Do you have
> issues with this?

Yes, it does not boot, no shell or getty.

> > diff --git a/package/gcc/4.8.5/891-fix-m68k-uclinux.patch b/package/gcc/4.8.5/891-fix-m68k-uclinux.patch
> > new file mode 100644
> > index 0000000..13bf0d9
> > --- /dev/null
> > +++ b/package/gcc/4.8.5/891-fix-m68k-uclinux.patch
> > @@ -0,0 +1,17 @@
> > +See here:
> > +https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53833
> 
> Giving a link is good, but it's still good to add a quick description
> of the patch nonetheless.

Okay.

> > diff --git a/package/gcc/gcc-final/gcc-final.mk b/package/gcc/gcc-final/gcc-final.mk
> > index 69fdc0c..f07d4a0 100644
> > --- a/package/gcc/gcc-final/gcc-final.mk
> > +++ b/package/gcc/gcc-final/gcc-final.mk
> > @@ -74,6 +74,14 @@ HOST_GCC_FINAL_CONF_OPTS += "--with-multilib-list=m4a,m4a-nofpu"
> >  HOST_GCC_FINAL_GCC_LIB_DIR = $(HOST_DIR)/usr/$(GNU_TARGET_NAME)/lib/!m4*
> >  endif
> >  
> > +# m68k/coldfire needs special configure options
> > +ifeq ($(BR2_m68k_m68k),y)
> > +HOST_GCC_INITIAL_CONF_OPTS += --with-arch=m68k --enable-multilib --with-system-zlib
> 
> You're in gcc-final, so touching HOST_GCC_INITIAL_CONF_OPTS looks weird.
> 
> You can remove the --with-arch part, is it already passed by
> package/gcc/gcc.mk:
> 
> ifneq ($(call qstrip,$(BR2_GCC_TARGET_ARCH)),)
> HOST_GCC_COMMON_CONF_OPTS += --with-arch=$(BR2_GCC_TARGET_ARCH)
> endif
> 
> Also, if you need to pass options to both the gcc-initial and
> gcc-final, you should do it in package/gcc/gcc.mk, by appending to
> HOST_GCC_COMMON_CONF_OPTS.
> 
> It would be good to have a better justification than "m68k/coldfire
> needs special configure options" to explain why --enable-multilib
> --with-system-zlib are needed.

Completely removed as not needed. :)

> > +# coldfire is not working without removing these object files from libgcc.a
> > +ifeq ($(BR2_m68k_cf),y)
> > +define HOST_GCC_FINAL_M68K_LIBGCC_FIXUP
> > +	find $(STAGING_DIR) -name libgcc.a -print | while read t; do $(GNU_TARGET_NAME)-ar dv "$t" _ctors.o; done
> 
> Yerk, this looks really ugly. Is this a known problem in upstream gcc?

Sorry, yes this is required. In the past I used a gcc wrapper and a
modified spec file, this is a more simple solution I got from
uClinux toolchain build script. I asked on the uClinux mailinglist
about this, but the technical reasons for this workaround are
unknown to at least Greg, which seems the only active uClinux
developer. So at the moment I would say, let keep it this way.
I like to have the linux-atomic.c ice stuff next to get fixed in gcc upstream.
The other m68k fix got applied to trunk recently.

Sometimes bugs in binutils/gcc needs 1-2 years to get fixed upstream, so don't give
up ;)
https://sourceware.org/bugzilla/show_bug.cgi?id=17334

> > +# m68k/coldfire needs special configure options
> > +ifeq ($(BR2_m68k_m68k),y)
> > +HOST_GCC_INITIAL_CONF_OPTS += --with-arch=m68k --enable-multilib --with-system-zlib
> > +endif
> > +ifeq ($(BR2_m68k_cf),y)
> > +HOST_GCC_INITIAL_CONF_OPTS += --with-arch=cf --enable-multilib --with-system-zlib
> > +endif
> 
> Same comments as above.
> 
> 
> >  #
> > +# m68k/coldfire definitions
> > +#
> > +
> > +ifeq ($(UCLIBC_TARGET_ARCH),m68k)
> > +
> > +# disable DOPIC for flat without separate data
> > +ifeq ($(BR2_BINFMT_FLAT_ONE),y)
> > +define UCLIBC_M68K_BINFMT_FLAT
> > +	$(call KCONFIG_DISABLE_OPT,DOPIC,$(@D)/.config)
> > +endef
> > +endif
> 
> In the end, isn't the removal of DOPIC necessary for all architectures
> when binfmt_flat is used? We did the same thing for ARMv7-M, so I'm
> wondering if we shouldn't make that generic.

It is not required for Blackfin binfmt_flat, so I would like to keep
it only for ARM and M68K for now. May be I will add some code to
make it automatically right inside uClibc-ng.

best regards
 Waldemar