Hi Guix,

attached is a patch blob providing the “embedded.scm” module.  I’m using
this cross-compiler semi-successfully to build so-called “patches” for
the Axoloti audio development/prototyping board.

I’m using the cross binutils at a particular git commit; the same
applies to “gcc-arm-none-eabi”, which takes the GCC sources from SVN.
This is done because these revisions are known to work.  Axoloti
upstream uses a binary cross-compiler toolchain release, which is
available here:

    https://launchpad.net/gcc-arm-embedded/4.9/4.9-2015-q2-update

The module also contains “newlib-arm-none-eabi” and
“newlib-nano-arm-none-eabi”, which is used instead of the glibc.

In “gnu/packages/bootstrap.scm” I made a tiny change to keep
“glibc-dynamic-linker” from failing.

Now, I have a problem with this toolchain: it doesn’t seem to work
properly.  While I can build “patches” for Axoloti that are linked with
the pre-compiled firmware from upstream, I cannot seem to create a
working firmware binary (that’s ChibiOS with extensions).  There are no
errors when I build it; it generates an elf file.  But when it is
uploaded to the board the system won’t boot.  I have to flash upstream’s
binary firmware with dfu-util to revive the board.

Generating “patches” on the other hand works fine.  It’s really just
this:

~~~~~~~~~~~
/gnu/store/p787lrv17m25v0cdrdzw66r9b7hk1109-gcc-cross-sans-libc-arm-none-eabi-4.9.3-1.224288/bin/arm-none-eabi-g++ -nostdlib -fno-exceptions -fno-rtti -mcpu=cortex-m4 -O3 -fomit-frame-pointer -falign-functions=16 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsingle-precision-constant -Wunused-parameter -DCORTEX_USE_FPU=TRUE -DTHUMB_PRESENT -mno-thumb-interwork -DTHUMB_NO_INTERWORKING -mthumb -DTHUMB -std=c++11 -DARM_MATH_CM4 -D__FPU_PRESENT -H -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/CMSIS/Include -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/ports/common/ARMCMx/CMSIS/include -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/ports/common/ARMCMx -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/ports/GCC/ARMCMx -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/ports/GCC/ARMCMx/STM32F4xx -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/kernel/include -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/include -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/platforms/STM32F4xx -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/platforms/STM32 -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/platforms/STM32/GPIOv2 -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/platforms/STM32/I2Cv1 -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/platforms/STM32/OTGv1 -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/platforms/STM32/RTCv2 -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/platforms/STM32/SPIv1 -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/platforms/STM32/TIMv1 -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/os/hal/platforms/STM32/USARTv1 -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/boards/ST_STM32F4_DISCOVERY -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios/ext/fatfs/src -I. -I/gnu/store/ysyi04kr6y4sbp5s6yyvpy3kl2yhppyh-axoloti-patcher-1.0.6/share/axoloti/chibios -Winvalid-pch -MD -MP --include /home/rekado/axoloti/build/xpatch.h -c /home/rekado/axoloti/build/xpatch.cpp -o /home/rekado/axoloti/build/xpatch.o 
~~~~~~~~~~~

Since the command that works does not involve the linker as far as I can
tell my guess is that the linker is somehow broken (or that maybe
linking with “newlib” instead “glibc” doesn’t quite work).

I have never before built cross-compilers and I don’t really know what
I’m doing.

If you have any suggestions I’d be glad to hear them!

~~ Ricardo