Date: Sun, 14 Jun 2015 12:13:45 -0700 From: Adrian Chadd <adrian@freebsd.org> To: "freebsd-embedded@freebsd.org" <embedded@freebsd.org>, "freebsd-mips@freebsd.org" <freebsd-mips@freebsd.org> Subject: Starting to cross-compile non-base software for MIPS - what it's like Message-ID: <CAJ-VmonSXYdLP_VpGh%2B3N_WfGwDLqWGcuPvOCf4VkOd0pJ5QWg@mail.gmail.com>
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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.
* yes, I tested the dropbear/dbclient binaries in a mips qemu VM (not
qemu-mips-user, but a full mips MALTA VM.) Both worked fine.
* the sysroot setup didn't correctly set the include path stuff right
- I need to chase that down. Ie, it was still searching in
/usr/include/ rather than ${SYSROOT}/usr/include/ . The library code
obeyed the library searching, except for that hardlink.
So, the very basics of "how can we cross compile things to run inside
a freebsd-mips machine" work fine. It's amusing and annoying that the
sysroot thing popped up. I do wonder if this class of problem keeps
popping up when people do builds from one freebsd version to another;
but I currently have no clear idea how to automate detecting this.
On the plus side, it did work.
So:
* I'll try to wrangle juli/bsdimp to review the libgcc change I have
so userland compiles using gcc-4.9 with warnings disabled.
* I'll try to wrangle juli/bsdimp to review the kernel changes needed
to compile up the kernel with gcc-4.9.
* 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.
* 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.
Then I'll worry about starting to convert a few ports to be native
cross building.
-a
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