#Compiling MODLFOW files with Pymake


**HOW TO FIND REQUIRED COMPILER FLAGS FOR COMPILING WITH gfortran 11.2 ON MACOS MONTEREY ?**

@ Theo Olsthoorn, 2021-11-01

Compilation and linking troubles on Big Sur because Apple changed things for compilers:
	no stdlib.h and stdio.h in /usr/include
	no direct access to dynamic libraries. It must now go through the dynamic library cache.

Therefore Pymake is no longer up-to-date and we have to alter the makefile that it generates to get the compiling and linking done.

**INCLUDE DIRECTORY**
First make sure that the include files are found by copiing them to the standard directory where they are searched

The coarse method is (which I did):
sudo ln -s /Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk/usr/include/*.h /usr/local/include

However, this may be a better (more hygienic way) to achieve the same effect
export CPATH=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/

or better, and simpler in the end, put an INCLUDEDIR directive in the make file and then use flag -I$(INCLUDEDIR) with the CFLAGS
INCLUDEDIR = /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/

**Apples new "dynamic link chache**
To use the dynamic link cache see below, where we let gcc tell what the location is of the cache (namely:)
-syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk

This information was found in the link: https://developer.apple.com/forums/thread/669094

Here is a terminal session that shows how to get the information on the "dynamic link cache" (i.e. the sysroot):

The dynamic library cache is shipped by Apple since MacOS Catalina.

“Most folks compile C programs using the compiler driver. For example:”

% sw_vers
ProductName: macOS
ProductVersion: 11.0.1
BuildVersion: 20B29
% xcode-select -p
/Applications/Xcode.app/Contents/Developer
% cat test.c
#include <unistd.h>

const unsigned char pmessagebuf[13] = "hello world\n";

int main (int argc, char* argv[])
{
write(STDOUT_FILENO, (void*)pmessagebuf, 12);
return(0);
}
% cc test.c -o test
% ./test
hello world

“If you want to compile each file separately, you can use the compiler driver for that too:”

% rm test
% cc -c test.c
% cc test.o -o test
% ./test
hello world

“If you want to explicitly run the linker, you’ll need to tell it what SDK to use. A good way to work out the exact syntax is to run the compiler driver with -v:”

% cc test.o -v -o test
Apple clang version 12.0.0 (clang-1200.0.32.27)
Target: x86_64-apple-darwin20.1.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld"
-demangle
-lto_library /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libLTO.dylib
-dynamic
-arch x86_64
-platform_version macos 11.0.0 11.0
-syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk
-o test
-L/usr/local/lib
test.o
-lSystem
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/lib/darwin/libclang_rt.osx.a

“The ‘secret sauce’ here is -syslibroot.”

(But in gfortran this option is -—sysroot)

The final solution is as follows:
Define in the makefile a variable SYSROOT = ….(copy the argument from above, as one of the options shown by cc test.o -v -o test)

And then put the option in the line that tells how to construct the program in the makefile (the optioni recognized by gcc is —sysroot,
so use that):

like so in the makefile
SYSLIBROOT = /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk


# Define the objects that make up mf2005
mf2005: $(OBJECTS)
	-$(F90) $(F90FLAGS) -o $(PROGRAM) --sysroot $(SYSLIBROOT) $(OBJECTS) $(SYSLIBS) -I$(OBJDIR) -J$(OBJDIR)