Re: cross compiling gsl for arm cortex M4 (nrf52)

[Julius Duin]

Hello Mark,
thanks a lot for the quick response, I am not entirely sure if I already got 
this right, after configuring with -I/crosscompilearea/gsl-2.7.1/include in c 
flags I will still get the errors in make -> those are not include but rather 
missing src file errors, e.g. undefined reference to `gsl_rng_get’ 
and many others like this. So including the path might let the compiler know 
where it can find headers but the src code for some things still seems missing.

though, I went to the gsl_rng header file and the definition of the function 
seems to be in the .h file anyways. 
my configure command is now 
./configure CC=/usr/local/gcc/bin/arm-none-eabi-gcc 
CXX=/usr/local/gcc/bin/arm-none-eabi-gcc 
LD=/usr/local/gcc/bin/arm-none-eabi-gcc AR=/usr/local/gcc/bin/arm-none-eabi-ar 
OBJCOPY=/usr/local/gcc/bin/arm-none-eabi-objcopy 
CFLAGS="-I/crosscompilearea/gsl-2.7.1/gsl -mthumb -march=armv7e-m 
-mfpu=fpv4-sp-d16 -mfloat-abi=soft" CXXFLAGS="-mthumb -march=armv7e-m 
-mfpu=fpv4-sp-d16 -mfloat-abi=soft" LDFLAGS="-I/crosscompilearea/gsl-2.7.1/gsl 
--specs=nano.specs --specs=nosys.specs -mthumb -march=armv7e-m 
-mfpu=fpv4-sp-d16 -mfloat-abi=soft" 
C_INCLUDE_PATH=“/crosscompilearea/gsl-2.7.1/gsl"  --target=arm-none-eabi 
--host=arm-none-eabi

I also always make clean/distclean after every attempt so that nothing else can 
go wrong. 

If you need a more detailed description of my approach please get back to me.
Best
Julius

> On 18.09.2023, at 16:33, Mark Galassi <mark@galassi.org> wrote:
> 
> 
> Dear Julius,
> 
> Your problem seems like it might have a straightforward solution.  Whenever 
> you do a lot of setting of CC and CXX and LD you might also want to set 
> C_INCLUDE_PATH and CPLUS_INCLUDE_PATH (and maybe when you get to linking also 
> LIBRARY_PATH).
> 
> I would try finding the full path to the gsl_minmax.h file.  Let's say it's 
> in /mycrosscompilearea/stuff/include/gsl/gsl_minmax.h.  Then, noting that 
> what's being #included is gsl/gsl_minmax.h, and I would say something like 
> C_INCLUDE_PATH=/mycrosscompilearea/stuff/include:$C_INCLUDE_PATH
> 
> And the same for LDFLAGS and (if you use C++) for CPLUS_INCLUDE_PATH.
> 
> You might also be able to put a -I option into the CFLAGS setting you are 
> already using.
> 
> And I would also investigate using pkg-config -- I have not used it in 
> cross-compiling, so it might not work for you, but you can set your 
> PKG_CONFIG_PATH to include /mycrosscompilearea/stuff/lib/wherever_gsl.pc_is 
> and then use the usual:
> 
> pkg-config gsl --cflags
> pkg-config gsl --libs
> 
> Feel free to contact me further if you want to look at this together.