Cross-compile to static lib (libgcrypt) for use on iOS

I have downloaded latest libgcrypt & libgpg-error libraries from https://www.gnupg.org/download/index.html. I have successfully built (command line) both libraries using ./configure --enable-static --disable-shared; make ; make install on my Mac (Mavericks w/OSX 10.10 & latest Xcode 6.1).

I can link just fine to these new libs from an OS X client app I am building. So far, so good. Just perfect. BUT, I also need to build an iOS client using same exact source code.

Questions:

1) What are the modifications to the command line build sequence for the library I would need to build a universal static library for the (simulator, Mac & iOS)? 2) Or do I need to build separate static libs for iOS? And if so, again, what command line magic would I need to accomplish getting the target architecture right?

Solution

Note that it is not possible to build a universal library that will work for both the iOS Simulator and macOS. iOS/Intel and macOS/Intel are not ABI compatible above the C runtime library (Libc). This answer serves to show you how to crosscompile autoconf based projects for iOS targets, and you can easily lipo the resulting static archives together.

You will want to do something like this:

#!/bin/bash -e -x

OPT_FLAGS="-Os -g3"
MAKE_JOBS=16

dobuild() {
    export CC="$(xcrun -find -sdk ${SDK} cc)"
    export CXX="$(xcrun -find -sdk ${SDK} cxx)"
    export CPP="$(xcrun -find -sdk ${SDK} cpp)"
    export CFLAGS="${HOST_FLAGS} ${OPT_FLAGS}"
    export CXXFLAGS="${HOST_FLAGS} ${OPT_FLAGS}"
    export LDFLAGS="${HOST_FLAGS}"

    ./configure --host=${CHOST} --prefix=${PREFIX} --enable-static --disable-shared

    make clean
    make -j${MAKE_JOBS}
    make install
}

SDK="iphoneos"
ARCH_FLAGS="-arch armv7"
HOST_FLAGS="${ARCH_FLAGS} -miphoneos-version-min=8.0 -isysroot $(xcrun -sdk ${SDK} --show-sdk-path)"
CHOST="arm-apple-darwin"
PREFIX="${HOME}/DEVICE_ARM"
dobuild

SDK="iphoneos"
ARCH_FLAGS="-arch arm64"
HOST_FLAGS="${ARCH_FLAGS} -miphoneos-version-min=8.0 -isysroot $(xcrun -sdk ${SDK} --show-sdk-path)"
CHOST="arm-apple-darwin"
PREFIX="${HOME}/DEVICE_ARM64"
dobuild

SDK="iphonesimulator"
ARCH_FLAGS="-arch i386"
HOST_FLAGS="${ARCH_FLAGS} -mios-simulator-version-min=8.0 -isysroot $(xcrun -sdk ${SDK} --show-sdk-path)"
CHOST="i386-apple-darwin"
PREFIX="${HOME}/SIM_i386"
dobuild

SDK="iphonesimulator"
ARCH_FLAGS="-arch x86_64"
HOST_FLAGS="${ARCH_FLAGS} -mios-simulator-version-min=8.0 -isysroot $(xcrun -sdk ${SDK} --show-sdk-path)"
CHOST="x86_64-apple-darwin"
PREFIX="${HOME}/SIM_x86_64"
dobuild

I just threw that script together and verified it works (with the addition of --disable-libpng and skipping tests) for pixman. You will probably need to customize it for libgcrypt, but it serves to show the general pattern for building autoconf/automake/glibtool based projects for iOS.

After building, you'll have content in ~/{DEVICE_ARM{,64},SIM_{i386,x86_64}} and you can either lipo the static libraries together or just use all of them in your project (the linker will emit warnings about missing slices for the "other" archives which you can ignore).

lipo -create -output lib.a DEVICE_ARM/lib/lib.a DEVICE_ARM64/lib/lib.a SIM_i386/lib/lib.a SIM_x86_64/lib/lib.a