How to build a toolchain for arm cortex-m and cortex-r

[rapsure]

So crossdev almost can build a functioning toolchain for embedded arm development. I do embedded arm development for my job so this is critical to have a fully functioning toolchain. Here is how to do it.

Step 1:

Code: Select all

crossdev --lenv 'USE="nano -nls -threads -unicode"' -s3 -t arm-unknown-eabi

Step 2:

Code: Select all

crossdev --lenv 'USE="nano -nls -threads -unicode"' --genv 'USE="cxx -nls -nptl -pch -pie -ssp" EXTRA_ECONF="--with-multilib-list=rmprofile --disable-decimal-float --disable-libffi --disable-libgomp --disable-libmudflap --disable-libquadmath --disable-shared --disable-threads --disable-tls"' -s4 -t arm-unknown-eabi

Step 3:

Code: Select all

emerge cross-arm-unknown-eabi/newlib

Step 4: to get gdb

Code: Select all

crossdev --lenv 'USE="nano -nls -threads -unicode"' --genv 'USE="cxx -nls -nptl -pch -pie -ssp" EXTRA_ECONF="--with-multilib-list=rmprofile --disable-decimal-float --disable-libffi --disable-libgomp --disable-libmudflap --disable-libquadmath --disable-shared --disable-threads --disable-tls"' -s4 --ex-gdb -t arm-unknown-eabi

Now you'll have a functioning multilib / multiarch for embedded arm development with small code output size. Maybe someday these changes can be incorporated into crossdev.

Maybe make this a sticky. I took a lot of time to figure out all of the switches and the process.

With changes to toolchain.eclass as of August 2018 you will need to edit the file to disable --enable-float=soft

Change on line 1116:

Code: Select all

        yes)   confgcc+=( --with-float=soft ) ;;

to

Code: Select all

        yes)    ;;

[eugene-bright]

Thanks for your post!
The eclass fix on it's way.
https://bugs.gentoo.org/666896

[KAMIKAZE_]

After upgrading I've got my micropython firmware build failing with:

CC build-PYBV11/pins_PYBV11.c
LINK build-PYBV11/firmware.elf
arm-none-eabi-ld: error: build-PYBV11/firmware.elf uses VFP register arguments, /usr/lib/gcc/arm-none-eabi/8.2.0/libgcc.a(_udivmoddi4.o) does not
arm-none-eabi-ld: failed to merge target specific data of file /usr/lib/gcc/arm-none-eabi/8.2.0/libgcc.a(_udivmoddi4.o)
make: *** [Makefile:528: build-PYBV11/firmware.elf] Error 1

[rapsure]

After upgrading I've got my micropython firmware build failing with:

That is because your comping with hardware fpu support and linking against a soft fpu gcc. The instuctions I gave above gives a multilib build of libc-nano and the smallest code size for a Cortex-M or Cortex-R.

[triffid_hunter]

I've found that lots of modern toolchains want arm-none-eabi to have hardfp support, however by default, cross-arm-none-eabi/newlib won't make hardfp libraries but it can be convinced to build them with a configure flag - that means we can make a arm-none-eabi toolchain with -mfloat-abi=soft,softfp,and hard support with this command:

Code: Select all

crossdev --lenv 'USE="nano -nls -threads -unicode" EXTRA_ECONF="--enable-newlib-hw-fp"' --genv 'USE="cxx -nls -nptl -pch -pie -ssp" EXTRA_ECONF="--with-multilib-list=rmprofile --disable-decimal-float --disable-libffi --disable-libgomp --disable-libmudflap --disable-libquadmath --disable-shared --disable-threads --disable-tls"' -s4 --ex-gdb -t arm-none-eabi

Note the added EXTRA_ECONF="--enable-newlib-hw-fp" under --lenv.

[rapsure]

So I've use the above process to create binaries for the nrf51, and nrf52 and any Cortex-M... architecture. Never had a problem. I could even find compiler bugs by comparing between several different versions.