cross-compiler 8.2.0 doesn't have {sysroot}/usr/include in its header search path

[avilleret]

with your 8.2.0 compiler I got :

$ echo | LANG=en_US.UTF-8 arm-linux-gnueabihf-gcc --sysroot=/home/antoine/dev/ofnode/sysroot -E -Wp,-v -
ignoring nonexistent directory "/opt/cross-pi-gcc-8.2.0/bin/../lib/gcc/arm-linux-gnueabihf/8.2.0/../../../../arm-linux-gnueabihf/sys-include"
ignoring duplicate directory "/opt/cross-pi-gcc-8.2.0/bin/../lib/gcc/../../lib/gcc/arm-linux-gnueabihf/8.2.0/include"
ignoring duplicate directory "/opt/cross-pi-gcc-8.2.0/bin/../lib/gcc/../../lib/gcc/arm-linux-gnueabihf/8.2.0/include-fixed"
ignoring nonexistent directory "/opt/cross-pi-gcc-8.2.0/bin/../lib/gcc/../../lib/gcc/arm-linux-gnueabihf/8.2.0/../../../../arm-linux-gnueabihf/sys-include"
ignoring duplicate directory "/opt/cross-pi-gcc-8.2.0/bin/../lib/gcc/../../lib/gcc/arm-linux-gnueabihf/8.2.0/../../../../arm-linux-gnueabihf/include"
#include "..." search starts here:
#include <...> search starts here:
 /opt/cross-pi-gcc-8.2.0/bin/../lib/gcc/arm-linux-gnueabihf/8.2.0/include
 /opt/cross-pi-gcc-8.2.0/bin/../lib/gcc/arm-linux-gnueabihf/8.2.0/include-fixed
 /opt/cross-pi-gcc-8.2.0/bin/../lib/gcc/arm-linux-gnueabihf/8.2.0/../../../../arm-linux-gnueabihf/include
End of search list.
# 1 "<stdin>"
# 1 "<built-in>"
# 1 "<command-line>"
# 31 "<command-line>"
# 1 "/opt/cross-pi-gcc-8.2.0/arm-linux-gnueabihf/include/stdc-predef.h" 1 3
# 32 "<command-line>" 2
# 1 "<stdin>"

while with the 8.1.0 I installed from archlinux repo I have :

$  echo | arm-linux-gnueabihf-gcc --sysroot=~/dev/ofnode/sysroot -E -Wp,-v -
ignoring nonexistent directory "~/dev/ofnode/sysroot/usr/arm-linux-gnueabihf/include"
ignoring nonexistent directory "~/dev/ofnode/sysroot/usr/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/arm-linux-gnueabihf/8.1.0/include
 /usr/lib/gcc/arm-linux-gnueabihf/8.1.0/include-fixed
 /usr/lib/gcc/arm-linux-gnueabihf/8.1.0/../../../../arm-linux-gnueabihf/include
End of search list.
# 1 "<stdin>"
# 1 "<built-in>"
# 1 "<command-line>"
# 31 "<command-line>"
# 1 "/usr/arm-linux-gnueabihf/include/stdc-predef.h" 1 3
# 32 "<command-line>" 2
# 1 "<stdin>"
[antoine@antoine-pc ~]$  echo | arm-linux-gnueabihf-gcc --sysroot=/home/antoine/dev/ofnode/sysroot -E -Wp,-v -
ignoring nonexistent directory "/home/antoine/dev/ofnode/sysroot/usr/arm-linux-gnueabihf/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/arm-linux-gnueabihf/8.1.0/include
 /usr/lib/gcc/arm-linux-gnueabihf/8.1.0/include-fixed
 /usr/lib/gcc/arm-linux-gnueabihf/8.1.0/../../../../arm-linux-gnueabihf/include
 /home/antoine/dev/ofnode/sysroot/usr/include
End of search list.
# 1 "<stdin>"
# 1 "<built-in>"
# 1 "<command-line>"
# 31 "<command-line>"
# 1 "/usr/arm-linux-gnueabihf/include/stdc-predef.h" 1 3
# 32 "<command-line>" 2
# 1 "<stdin>"

Please note that in the second case, #include <...> search starts here: lists /home/antoine/dev/ofnode/sysroot/usr/include while the first (8.2.0) doesn't.

While I can manually add the include path with a -I flag, it makes this compiler hard to use with CMake which strips off "${CMAKE_SYSROOT}/usr/include".
see related issue here : https://gitlab.kitware.com/cmake/cmake/issues/17966

[abhiTronix]

@avilleret Can share the GCC 8.1.0 link that you tried from archlinux repo?

[avilleret]

it's in AUR repo : https://aur.archlinux.org/packages/arm-linux-gnueabihf-gcc/

[abhiTronix]

@avilleret I thought you're using custom Cross-Compiler similar this repo. ,

The main reason behind this bug/error is that the Official Cross Compiler install files directly to the default system root directory, i.e /usr/ or /usr/local/ and Cmake is made explicitly to work with these paths/configurations only and not with custom paths/configurations, to prevent any broken binding. Therefore any custom Cross-Compiler(like provided here) fails to work in this scenario as its default installation path is /opt/ normally, not the root directory.

So, unfortunately, if you want to use GCC 8.2.0 Cross-Compiler with Cmake on your system, you yourself have compiled & installed it from source to the root directory of your machine.

[abhiTronix]

@avilleret They're working on a fix here(in progress): https://gitlab.kitware.com/cmake/cmake/merge_requests/2716

[avilleret]

it is indeed possible to use your Crosscompiler build with CMake (and I thanks you a lot for sharing)
I have to disable the CMake's implicit directory feature by injecting the following lines into my toolchain file

unset(CMAKE_C_IMPLICIT_INCLUDE_DIRECTORIES)
unset(CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES)

I was unsure if its a bug (or a feature) of CMake or if it's a lake of configuration on your side.
Now I'm fixed :-)
Thanks for the quick reply, thanks for the explanation, and thanks again for all this wonderful work.