How to build OpenBLAS for iPhone iOS (ARMv8)

How to build OpenBLAS for iPhone/iOS

Go to the directory where you unpacked OpenBLAS.
In file c_check look for the section that looks like

     $cross_suffix = "";

     if (dirname($compiler_name) ne ".") {
         $cross_suffix .= dirname($compiler_name) . "/";
     }

     if (basename($compiler_name) =~ /([^\s]*-)(.*)/) {
         $cross_suffix .= $1;
     }

and add the following line after it, adjusting the path as necessary for your Xcode installation:

    $cross_suffix = "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/";

You need this because we will provide CC with arguments and Perl function for extracting directory doesn't work well.

Next, create a file with the following content:

     TOOLCHAIN_PATH=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
     SYSROOT_PATH=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS10.2.sdk
     make TARGET=ARMV8 BINARY=64 HOSTCC=clang CC="$TOOLCHAIN_PATH/clang -isysroot $SYSROOT_PATH -arch arm64" NOFORTRAN=1 libs

(again adjust the TOOLCHAIN_PATH and SYSROOT_PATH as necessary for your installation, e.g. change the version number of the SDK to what you have installed) and execute this file to build the library.