[R-SIG-Mac] error: unrecognized option ‘-arch’ -- suggestion!

[Peder Axensten]

The compiler (clang) and linker that Apple includes (with Xcode) uses the argument -arch to specify the architecture to build for. This is not recognized by, for instance, the gcc compilers. Because this argument is 'hardcoded' into the Makeconfig files, it is an involved process to compile libraries for R with any other compiler.

Either all all `-arch i386` and `-arch x86_64` must be removed from these files (this must be done every time R is updated) or you create a file `~/.R/Makevars` with something like
~~~~~~~
MYARCH = -arch x86_64

# Comment the next line to return to the original setting:
MYARCH = 

CC = gcc $(MYARCH) -std=gnu99
CXX=g++ $(MYARCH)
CXXCPP = g++ $(MYARCH) -E
FC = gfortran $(MYARCH)
F77 = gfortran $(MYARCH)
OBJC = gcc $(MYARCH)
OBJCXX = g++ $(MYARCH)

DYLIB_LD = gcc $(MYARCH) -std=gnu99
MAIN_LD = gcc $(MYARCH) -std=gnu99
SHLIB_CXXLD = g++ $(MYARCH)
SHLIB_FCLD = gfortran $(MYARCH)
SHLIB_LD = gcc $(MYARCH) -std=gnu99
~~~~~~~
Unfortunately, a few instances of `-arch` are outside the variables and can not be reached this way.



My suggestion is that the Makeconfig files are slightly changed:

- Change all `-arch i386` or `-arch x86_64` in these files to `$(MYARCH)`.
- Add a line `MYARCH = -arch x86_64` or `MYARCH = -arch i386`, respectively, to the top of these files.

No functionality is changed but using another compiler is more compatible and simpler as only MYARCH would need to be predefined.



Even better would be to be able to specify the compiler set to be used by using a variable (and handle the architecture accordingly), but I know to little about make files to come up with a constructive suggestion. Probably something like using
PREFIX = 
GCC = $(PREFIX)gcc $(MYARCH)
GPP = $(PREFIX)g++ $(MYARCH)
GFORTRAN = $(PREFIX)gfortran $(MYARCH)
and then using them when defining CC, XXX, etc.

No functionality would be changed, but a different set of compilers could be used just by changing PREFIX and MYARCH.

Best regards,

Peder Axensten
Research engineer

Swedish University of Agricultural Sciences
Dept. of Forest Resource Management
Remote Sensing
se-90183 Umeå
Sweden
Visiting address: Skogsmarksgränd