Re: [Ksummit-discuss] [CORE TOPIC] More useful types in the linux kernel

[David Howells <dhowells@redhat.com>]

Linus Walleij <linus.walleij@linaro.org> wrote:

> So it works, but still of course this thing is there:
> 
> rpm -ql gcc-arm-linux-gnu-6.1.1-1.fc24.x86_64
> (...)
> /usr/lib/gcc/arm-linux-gnueabi/6.1.1/libgcc.a

Some people really wanted libgcc libraries.  Even some kernel arches require
them.

> I suspect these things are implicitly compiled for one and only one ISA?
> I honestly don't know how to even check which one. Does it use
> hardfloat? Or has this problem of targetting several ISAs with a .a
> file been fixes since I looked at it last?
> 
> I need to cross-compile ARMv4, ARMv5, ARMv6, ARMv7 and
> ARMv8 for my systems. (Sorry for all old crap I'm keeping it's just
> my job...)

The arm- compiler is built with:

	CONFIG_FLAGS="--with-tune=cortex-a8 --with-arch=armv7-a \
		--with-float=hard --with-fpu=vfpv3-d16 --with-abi=aapcs-linux"

I can probably add a --with-multilib-list= option to build multiple variants
as I do for sh and sh64:

	sh-*)
	    CONFIG_FLAGS=--with-multilib-list=m1,m2,m2e,m2a,m2a-single,m4,m4-single,m4-single-only,m4-nofpu
	    ;;
	sh4-*)
	    CONFIG_FLAGS=--with-multilib-list=m4,m4-single,m4-single-only,m4-nofpu
	    ;;

if someone tells me what they'd like to see on there.  In the sh case, this
gives me all of:

	/usr/lib/gcc/sh-linux-gnu/5.3.1/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/m2/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/m2e/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/m4-nofpu/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/m4-single-only/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/m4-single/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/m4/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/mb/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/mb/m2/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/mb/m2a-single/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/mb/m2a/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/mb/m2e/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/mb/m4-nofpu/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/mb/m4-single-only/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/mb/m4-single/libgcc.a
	/usr/lib/gcc/sh-linux-gnu/5.3.1/mb/m4/libgcc.a

> That ABI problem is then manifolded if I would want to do anything
> userspace, so I keep a whole range of tailored cross compilers and
> prebuilt C libraries around that I know "just work", but I guess will
> grow increasingly hard to maintain and it feels pretty unelegant at
> times.

Yeah.  It's made more fun by the fact that if I want to do a general compiler
SRPM that covers all the arches fully bootstrapped with C libraries, not every
arch is supported by glibc, so I have to include uClibc as well for those
arches.

Take sh as mentioned above, that has at least 16 different potential
userspaces by the libgcc count.

> Is there a way for a distribution to provide a proper set of
> ISA-specific stuff alongside a crosscompiler, if the crosscompiler
> supports several different ISAs, like the ARMvN variants do?

It *ought* to be possible to build C libraries separately, given an available
cross-compiler - except that the gcc build wants stuff from the C library
you're using.  Having talked to some gcc people about this before, IIRC, it's
something that could be managed without - if someone's willing to do the work
to make gcc no longer require it.

David