Ricardo Wurmus <rekado@elephly.net> writes:

> Hi Marius,
>
>> Efraim Flashner <efraim@flashner.co.il> writes:
>>
>>> On Sat, Jan 19, 2019 at 07:09:04PM +0200, Efraim Flashner wrote:
>>>> 
>>>> I'm going to see if I can build hello --target=arm-linux-gnueabihf next
>>>> and see how that works.
>>>
>>> When I get to gcc-cross-arm-linux-gnueabihf it fails during configure,
>>> cannot find gmp.h. Looking at (gnu packages cross-base), I don't think
>>> there are any package-inputs for xgcc. I still thought gcc bundled its
>>> own gmp et. al.
>>
>> I'm happy to report that the cross-compilation issues are resolved with
>> this trivial patch:
>>
>> 2 files changed, 5 insertions(+), 11 deletions(-)
>> gnu/build/cross-toolchain.scm | 9 +++------
>> gnu/packages/cross-base.scm   | 7 ++-----
>>
>> modified   gnu/build/cross-toolchain.scm
>> @@ -36,11 +36,8 @@
>>  
>>  (define %gcc-include-paths
>>    ;; Environment variables for header search paths.
>> -  ;; Note: See <http://bugs.gnu.org/22186> for why not 'CPATH'.
>> -  '("C_INCLUDE_PATH"
>> -    "CPLUS_INCLUDE_PATH"
>> -    "OBJC_INCLUDE_PATH"
>> -    "OBJCPLUS_INCLUDE_PATH"))
>> +  ;; Note: See <http://bugs.gnu.org/30756> for why not 'C_INCLUDE_PATH' & co.
>> +  '("CPATH"))
>>  
>>  (define %gcc-cross-include-paths
>>    ;; Search path for target headers when cross-compiling.
>> @@ -179,7 +176,7 @@ a target triplet."
>>              ;; header" such that #include_next does the right thing.
>>              (for-each (lambda (var)
>>                          (setenv var (string-append libc "/include")))
>> -                      '("C_INCLUDE_PATH" "CPLUS_INCLUDE_PATH")))
>> +                      '("CROSS_C_INCLUDE_PATH" "CROSS_CPLUS_INCLUDE_PATH")))
>>            #t)))
>>      (add-after 'install 'make-cross-binutils-visible
>>        (cut make-cross-binutils-visible #:target target <...>))
>> modified   gnu/packages/cross-base.scm
>> @@ -51,11 +51,8 @@
>>  
>>  (define %gcc-include-paths
>>    ;; Environment variables for header search paths.
>> -  ;; Note: See <http://bugs.gnu.org/22186> for why not 'CPATH'.
>> -  '("C_INCLUDE_PATH"
>> -    "CPLUS_INCLUDE_PATH"
>> -    "OBJC_INCLUDE_PATH"
>> -    "OBJCPLUS_INCLUDE_PATH"))
>> +  ;; Note: See <http://bugs.gnu.org/30756> for why not 'C_INCLUDE_PATH' & co.
>> +  '("CPATH"))
>>  
>>  (define %gcc-cross-include-paths
>>    ;; Search path for target headers when cross-compiling.
>>
>> [back]
>> Silly me for not catching the CROSS_C_INCLUDE_PATH issue earlier.  But,
>> at least I got to know the GCC build processes and GDB better...  ;-)
>>
>> I will commit this series shortly and work on a followup patch that
>> removes the various GCC5/C++14 workarounds in one go.
>
> Will this break compilation with GCC5 and older, when they are installed
> in a profile or used as inputs?  Do we need copies of these variables
> and use different variants for different compiler versions?

I believe using (CROSS_)CPATH will work for all GCC versions, whereas
(CROSS_)C_INCLUDE_PATH are broken for GCC >= 6.

We do use C_INCLUDE_PATH for GCC < 6 in (gnu packages gcc), but I don't
think the added complexity is worth it for the cross-compiler
infrastructure.