Hi Ludo,
thanks for the hints.
> Ricardo Wurmus <rek...@elephly.net> skribis:
>
>> The latest version includes C++ sources for the firmware.
>> Unfortunately, our “arm-none-eabi” cross-compiler package does not
>> build libstdc++, nor does it come with any of the required C++ headers
>> like “cmath”.
>>
>> So I tried to change our “arm-none-eabi” cross-compiler packages to also
>> build and install libstdc++ but failed in a multitude of ways. The end
>> result is always that either the compiler fails to build (e.g. when
>> enabling libstdc++ via configure flags) or that the compiler fails to
>> find the header files that are included via “#include_next” directives
>> (e.g. when building libstdc++ as a separate package).
>>
>> Could someone with GCC experience give me a hint despite my vague
>> problem description?
>
> libstdc++ itself can probably be cross-built with:
>
> guix build libstdc++ --target=arm-none-eabi
I created a package variant like this:
--8<---------------cut here---------------start------------->8---
(define-public libstdc++-arm-none-eabi
(let* ((xgcc gcc-arm-none-eabi-6)
(libstdc++ (make-libstdc++ xgcc)))
(package (inherit libstdc++)
(name "libstdc++-arm-none-eabi")
(arguments
(substitute-keyword-arguments (package-arguments libstdc++)
((#:configure-flags flags)
``("--target=arm-none-eabi"
"--disable-libstdcxx-pch"
,(string-append "--with-gxx-include-dir="
(assoc-ref %outputs "out")
"/arm-none-eabi/include"))))))))
--8<---------------cut here---------------end--------------->8---
And adding it to the inputs for the Axoloti firmware seems to be fine
for a while until it fails to find headers with “#include_next”. I’ll
try to gather some better error messages.
> The problem is getting a cross-g++. I suspect libstdc++ sorta relies on
> having a “real” libc, which is why we normally do things like:
>
> (let ((triplet "arm-linux-gnueabihf"))
> (cross-gcc triplet
> (cross-binutils triplet)
> (cross-libc triplet))))
>
> where the final ‘cross-gcc’ has C++ support.
I find this confusing because the binary release of the arm-none-eabi
cross-compiler includes the libstdc++ headers — and it doesn’t appear to
use the GNU libc at all. It includes two libc variants which were both
derived from newlib (regular and “nano” configurations).
> I’m not sure if it makes sense for the board you’re targeting, but maybe
> you could try building with a full-blown cross-gcc like this?
I can give it a try but I don’t think it makes sense for the board.
It’s not supposed to use anything but the special implementations of
newlib-nano.
--
Ricardo
GPG: BCA6 89B6 3655 3801 C3C6 2150 197A 5888 235F ACAC
https://elephly.net
