Starting to cross-compile non-base software for MIPS - what it's like

[Michael Vale]

Here is onething that can be added under .if defined(X_BUILD_FOR), either as an .include e.g. bsd.cross.mk. or just paste it in there.  if X_BUILD_FOR /is/ defined, configure --host mips-freebsd-* etc will already be done if you just invoke a normal ports build rather than running configure manually from port/work/.
 
I know it's not perfect, but the only thing that needs and overview is the declaration of SYSROOT.  I used ${LOCALBASE} to define the right position, i'm unsure if this is correct.
 
---------------------------- bsd.cross.mk ----------------------------------------------------------------------------
 
.if exist(/usr/${X_BUILD_FOR}/usr/bin/${X_BUILD_FOR}-portbld-freebsd11.0-gcc) then \
MAKE_ENV+= CPU_ARGS="-march=${X_BUILD_FOR}"
  INCS="-l${SRCDIR}/../root/${X_BUILD_FOR}
.else
IGNORE= Install gcc with mips support from ports first.
.if FLOAT="hard" then \
MAKE_ENV+= CPU_ARGS="-mhard-float, -Wa,-mhard-float"
.else \
MAKE_ENV+= CPU_ARGS="-msoft-float, -Wa,-msoft-float"
MAKE_ENV+=  CROSS_COMPILE="${X_BUILD_FOR}-portbld-freebsd${OS_REL} \
  CC=${CROSS_COMPILE}-gcc \
  CXX=${CROSS_COMPILE}-g++ \
  LD=${X_BUILD_FOR}-freebsd-ld \
  AR=${X_BUILD_FOR}-freebsd-ar \
  RANLIB=${X_BUILD_FOR}-freebsd-ranlib \
  STRIP=${X_BUILD_FOR}-freebsd-strip \
  SYSROOT=${LOCALBASE}/${X_BUILD_FOR}/ \
  CFLAGS="--sysroot=$SYSROOT ${CPU_ARGS} ${INCS} -O"
  CXXFLAGS="--sysroot=$SYSROOM ${CPU_ARGS} ${INCS} -O"
 
> Date: Mon, 15 Jun 2015 11:45:00 -0700
> Subject: Re: Starting to cross-compile non-base software for MIPS - what it's like
> From: adrian at freebsd.org
> To: imp at bsdimp.com
> CC: embedded at freebsd.org; freebsd-mips at freebsd.org
> 
> On 15 June 2015 at 10:23, Warner Losh <imp at bsdimp.com> wrote:
> >
> >> On Jun 14, 2015, at 1:13 PM, Adrian Chadd <adrian at freebsd.org> wrote:
> >>
> >> Hi!
> >>
> >> I've been hacking at cross compiling things on FreeBSD for a while,
> >> and I have made some progress. This email is less of a "how you can do
> >> it" and more of a "these are the roadblocks that prevent it from
> >> working out of the box."
> >>
> >> I'm using gcc-4.9.2 from ports - there's a cross compiler for
> >> mips/mips64, and there's mips-binutils/mips64-binutils. I'm using
> >> those to compile world and kernel. The kernel works; world requires
> >> some patching to compile. I'll write a post when I have a complete
> >> system booting/running from gcc-4.9.2.
> >>
> >> My test application is dropbear. Ie, I'm cross-compiling dropbear for
> >> mips from freebsd/i386.
> >>
> >> * There are some issues in libgcc - I have a patch that I've emailed
> >> out for review. I'll do some more testing and commit it next week when
> >> I know it works.
> >> * There are some environment variables that need to be set before I
> >> compile dropbear. Here's what it looks like:
> >>
> >> CPU_ARGS="-march=mips32 -msoft-float -Wa,-msoft-float"
> >> INCS="-I/home/adrian/work/freebsd/head-embedded-2/root/mips/usr/include"
> >>
> >> export CROSS_COMPILE=mips-portbld-freebsd11.0
> >> export CC=${CROSS_COMPILE}-gcc
> >> export CXX=${CROSS_COMPILE}-g++
> >> #export LD=${CROSS_COMPILE}-ld
> >> #export AR=${CROSS_COMPILE}-ar
> >> #export RANLIB=${CROSS_COMPILE}-ranlib
> >> #export STRIP=${CROSS_COMPILE}-strip
> >> export LD=mips-freebsd-l
> >> export AR=mips-freebsd-ar
> >> export RANLIB=mips-freebsd-ranlib
> >> export STRIP=mips-freebsd-strip
> >> export SYSROOT=/home/adrian/work/freebsd/head-embedded-2/root/mips/
> >> export CFLAGS="--sysroot=$SYSROOT ${CPU_ARGS} ${INCS} -O"
> >> export CXXFLAGS="--sysroot=$SYSROOT ${CPU_ARGS} ${INCS} -O"
> >> export CPPFLAGS="--sysroot=$SYSROOT ${CPU_ARGS} ${INCS} -O"
> >> export LDFLAGS=--sysroot=$SYSROOT
> >>
> >> # now run:
> >> # /configure --host=mips-portbld-freebsd11.0
> >> # gmake
> >>
> >> ... then I hit a problem with how we populate links in /usr/lib and
> >> such. TL;DR - the symlinks we use are not relative paths, they're
> >> absolute paths - and this makes cross building using sysroot /
> >> explicit library paths fail to work right. Sigh. In particular, I
> >> needed to manually undo the libgcc symlink for it to compile.
> >> compilation complained about other libraries, but the resulting
> >> binaries did run.
> >
> > That’s one of about 6 reasons that what we produce isn’t a
> > sysroot. We need to create a sysroot target that’s very close
> > to the xdev targets with all the compiler bits stripped out. We’re
> > close though. I have about 1/2 of the patch needed to remove
> > xdev entirely and replace it with sysroot.
> 
> Sweet.
> 
> > You shouldn’t need the INCS args if you have a proper sysroot.
> > And the CPU_ARGS is an indication we’re building our port
> > incorrectly. This is the same feedback I gave on the kernel
> > make changes you suggested.
> 
> It looks like a proper sysroot - I think it's just the dynamic sysroot
> stuff being broken.
> 
> > I’ve had hacks like this for “simple” arts for years. It’s why I wrote
> > xdev in the first place. I had it working in the FreeBSD 6 time frame
> > for cross building some ports. But once you get past a certain
> > class of very well behaved ports, it goes to hell in a hurry.
> 
> 
> >> * I'll try to wrangle juli/bsdimp to review the kernel changes needed
> >> to compile up the kernel with gcc-4.9.
> >
> > I’ve already reviewed that one. gcc isn’t being compiled correctly
> > and that need to be fixed. This is the forth time I’ve given this
> > feedback.
> 
> There are some other issues too. The softfloat/hardfloat stuff reared
> its head - in order to avoid assembler warnings we have to manually
> set it, but then the floating point register accesses in fp.S /
> swtch.S generate errors. I've worked around that for now, but I need
> to dig into why the warnings are generated in the first case.
> 
> >> * I'd like some help / comments on what we can do about the absolute
> >> symlinks used for various things inside an installed root. Ideally
> >> we'd have an option that would let us populate only relative links -
> >> that'd instantly make this problem go away.
> >
> > All installworld-ish targets should use relative path symbolic links.
> > The fact they are using absolute paths is a bug. In the FreeBSD 6
> > time frame, I fought this battle at work and it wasn’t hard to fix. I
> > no longer have access to those sources, and I honestly can’t
> > recall how I fixed it (it may have been in a post-processing
> > step).
> 
> I'd love to get this fixed and into the tree.
> 
> >> * I'll go hit up bapt and some netbsd friends for some help with
> >> expected sysroot behaviour on gcc/binutils. It's possible there are
> >> still bugs with the dynamic sysroot (ie, when you don't compile your
> >> toolchain with an explicit sysroot to something other than '/') that
> >> need addressing.
> >
> > bapt and I have been talking about this for a while. We’ve both been
> > busy doing other things so haven’t focused on it other than in off
> > moments.
> >
> >> Then I'll worry about starting to convert a few ports to be native
> >> cross building.
> >
> > You should talk to bapt about the rather extensive work he’s done
> > in this area, which is why I’ve looked at transitioning the xdev
> > support to just sysroot support.
> 
> I have been too! fear not. That's how I got this far!
> 
> 
> -a
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