How do i compile a static library (fat) for armv6, armv7 and i386

Question

I know this question has been posed several times, but my goal is slightly different with regard to what I have found searching the web. Specifically, I am already able to build a static library for iPhone, but the final fat file I am able to build only contains arm and i386 architectures (and I am not sure to what arm refers: is v6 or v7?). I am not able to compile specifically for armv6 and armv7 and them merge both architectures using lipo. The lipo tool complains that the same architecture (arm, not armv6 or armv7) is present in both the armv6 and armv7 libraries.

Can someone explain exactly how to build for armv6 and armv7, and them merge these libraries into a fat file using lipo?

EDIT: I need to build not using Xcode but compiling directly a traditional unix library.

Answer 1

Make sure to have your build settings set to Valid Architectures: armv6 armv7 and Architectures: Optimized (armv6 armv7). This should result in a binary optimized for both v6 & v7. If you're not sure it worked out, just set the Architectures: Standard (armv6) and compare the file sizes. Optimized should produce double the size (when I remember rightly).

You also always can use lipo -info on your binary to see all the included architecures.

Running it on a distribution build of my app gives me:

ullrich ~/Code/.../build/Distribution-iphoneos/My.app (streaming)$ lipo -info My
Architectures in the fat file: My are: armv6 armv7 

Answer 2

Just use libtool to link the two arm6 and arm7 versions together - its what XCode does. However you will have problems if you try to combine these static libraries into a new super-library. If you need to do that then read this.

If you are doing this already, that would be why lipo is complaining that your "armv6" library contains both armv6 and armv7. My post has a fix that will probably be easier for you since you don't use XCode, but basically you use lipo -extract to make sure you have a thin armv6 library and a thin armv7 library before you go any further.

Answer 3

There doesn't seem to be a need to extract from the fat library before rejoining any more (as described in jamie's answer). I'm using the final 4.0 SDK from apple, which appear to create the fat armv6/armv7 libraries by default.

I was previously specifying the architecture for the input lib like so:

$DEVROOT/usr/bin/lipo -arch arm $PROJECT_DIR/buildlib/Release-iphoneos/lib.a -arch i386 $PROJECT_DIR/buildlib/Release-iphonesimulator/lib.a -create -output $PROJECT_DIR/buildlib/lib.a

This fails on the later SDKs, but removing the architecture from the (now fat) arm lib works fine:

$DEVROOT/usr/bin/lipo $PROJECT_DIR/buildlib/Release-iphoneos/lib.a -arch i386 $PROJECT_DIR/buildlib/Release-iphonesimulator/lib.a -create -output $PROJECT_DIR/buildlib/lib.a

Lipo must now be able to detect the architectures in the fat libraries.