Xcode - symbol(s) not found for architecture x86_64 (iOS Lib)

I had the same trouble with building static library.
Finally I have found the basic solution. (You need to build universal library for x86_64/armv7/armv7s/arm64)

1) Click on the project file
2) Click on the target
3) Open "Build Phases"
4) Open "Run Script"
5) Add "/bin/sh" and the script below

############################################ c.f. http://stackoverflow.com/questions/3520977/build-fat-static-library-device-simulator-using-xcode-and-sdk-4## Version 2.7## Latest Change:# - Supports iPhone 5 / iPod Touch 5 (uses Apple's workaround to lipo bug)## Purpose:#   Automatically create a Universal static library for iPhone + iPad + iPhone Simulator from within XCode## Author: Adam Martin - http://twitter.com/redglassesapps# Based on: original script from Eonil (main changes: Eonil's script WILL NOT WORK in Xcode GUI - it WILL CRASH YOUR COMPUTER)#set -eset -o pipefail#################[ Tests: helps workaround any future bugs in Xcode ]#########DEBUG_THIS_SCRIPT="false"if [ $DEBUG_THIS_SCRIPT = "true" ]thenecho "########### TESTS #############"echo "Use the following variables when debugging this script; note that they may change on recursions"echo "BUILD_DIR = $BUILD_DIR"echo "BUILD_ROOT = $BUILD_ROOT"echo "CONFIGURATION_BUILD_DIR = $CONFIGURATION_BUILD_DIR"echo "BUILT_PRODUCTS_DIR = $BUILT_PRODUCTS_DIR"echo "CONFIGURATION_TEMP_DIR = $CONFIGURATION_TEMP_DIR"echo "TARGET_BUILD_DIR = $TARGET_BUILD_DIR"fi#####################[ part 1 ]################### First, work out the BASESDK version number (NB: Apple ought to report this, but they hide it)#    (incidental: searching for substrings in sh is a nightmare! Sob)SDK_VERSION=$(echo ${SDK_NAME} | grep -o '.\{3\}$')# Next, work out if we're in SIM or DEVICEif [ ${PLATFORM_NAME} = "iphonesimulator" ]thenOTHER_SDK_TO_BUILD=iphoneos${SDK_VERSION}elseOTHER_SDK_TO_BUILD=iphonesimulator${SDK_VERSION}fiecho "XCode has selected SDK: ${PLATFORM_NAME} with version: ${SDK_VERSION} (although back-targetting: ${IPHONEOS_DEPLOYMENT_TARGET})"echo "...therefore, OTHER_SDK_TO_BUILD = ${OTHER_SDK_TO_BUILD}"######################[ end of part 1 ]#######################################[ part 2 ]#################### IF this is the original invocation, invoke WHATEVER other builds are required## Xcode is already building ONE target...## ...but this is a LIBRARY, so Apple is wrong to set it to build just one.# ...we need to build ALL targets# ...we MUST NOT re-build the target that is ALREADY being built: Xcode WILL CRASH YOUR COMPUTER if you try this (infinite recursion!)### So: build ONLY the missing platforms/configurations.if [ "true" == ${ALREADYINVOKED:-false} ]thenecho "RECURSION: I am NOT the root invocation, so I'm NOT going to recurse"else# CRITICAL:# Prevent infinite recursion (Xcode sucks)export ALREADYINVOKED="true"echo "RECURSION: I am the root ... recursing all missing build targets NOW..."echo "RECURSION: ...about to invoke: xcodebuild -configuration \"${CONFIGURATION}\" -project \"${PROJECT_NAME}.xcodeproj\" -target \"${TARGET_NAME}\" -sdk \"${OTHER_SDK_TO_BUILD}\" ${ACTION} RUN_CLANG_STATIC_ANALYZER=NO" BUILD_DIR=\"${BUILD_DIR}\" BUILD_ROOT=\"${BUILD_ROOT}\" SYMROOT=\"${SYMROOT}\"xcodebuild -configuration "${CONFIGURATION}" -project "${PROJECT_NAME}.xcodeproj" -target "${TARGET_NAME}" -sdk "${OTHER_SDK_TO_BUILD}" ${ACTION} RUN_CLANG_STATIC_ANALYZER=NO BUILD_DIR="${BUILD_DIR}" BUILD_ROOT="${BUILD_ROOT}" SYMROOT="${SYMROOT}"ACTION="build"#Merge all platform binaries as a fat binary for each configurations.# Calculate where the (multiple) built files are coming from:CURRENTCONFIG_DEVICE_DIR=${SYMROOT}/${CONFIGURATION}-iphoneosCURRENTCONFIG_SIMULATOR_DIR=${SYMROOT}/${CONFIGURATION}-iphonesimulatorecho "Taking device build from: ${CURRENTCONFIG_DEVICE_DIR}"echo "Taking simulator build from: ${CURRENTCONFIG_SIMULATOR_DIR}"CREATING_UNIVERSAL_DIR=${SYMROOT}/${CONFIGURATION}-universalecho "...I will output a universal build to: ${CREATING_UNIVERSAL_DIR}"# ... remove the products of previous runs of this script#      NB: this directory is ONLY created by this script - it should be safe to delete!rm -rf "${CREATING_UNIVERSAL_DIR}"mkdir "${CREATING_UNIVERSAL_DIR}"#echo "lipo: for current configuration (${CONFIGURATION}) creating output file: ${CREATING_UNIVERSAL_DIR}/${EXECUTABLE_NAME}"xcrun -sdk iphoneos lipo -create -output "${CREATING_UNIVERSAL_DIR}/${EXECUTABLE_NAME}" "${CURRENTCONFIG_DEVICE_DIR}/${EXECUTABLE_NAME}" "${CURRENTCONFIG_SIMULATOR_DIR}/${EXECUTABLE_NAME}"########### Added: StackOverflow suggestion to also copy "include" files#    (untested, but should work OK)#echo "Fetching headers from ${PUBLIC_HEADERS_FOLDER_PATH}"echo "  (if you embed your library project in another project, you will need to add"echo "   a "User Search Headers" build setting of: (NB INCLUDE THE DOUBLE QUOTES BELOW!)"echo '        "$(TARGET_BUILD_DIR)/usr/local/include/"'if [ -d "${CURRENTCONFIG_DEVICE_DIR}${PUBLIC_HEADERS_FOLDER_PATH}" ]thenmkdir -p "${CREATING_UNIVERSAL_DIR}${PUBLIC_HEADERS_FOLDER_PATH}"# * needs to be outside the double quotes?cp -r "${CURRENTCONFIG_DEVICE_DIR}${PUBLIC_HEADERS_FOLDER_PATH}"* "${CREATING_UNIVERSAL_DIR}${PUBLIC_HEADERS_FOLDER_PATH}"fifi

6) Hit "cmd + B" (Build Project)

7) Open Product in Finder

8) Navigate 1 directory up ("cmd + ↑"), and you will see "Release-universal" directory.

There will be your "fat/universal" library, You are ready to go!

I encountered this with a framework lib I'm using in one of my apps, when I tried to test it in iPhone Retina 64bit simulator.

I simply added x86_64 as an architecture to build for and set it to always build for all architectures. Worked a charm.

The lipo tool can not only create fat mach-o binaries, but it can inspect them:xcrun lipo -info /path/to/libThing.a

This will output what architectures are in the file. Before you join binaries using lipo, run this to make sure the architectures you expect are present. It's also a good idea to run this on the product of a fat binary join.

In your case you need:

iPhoneSDK Configuration:armv7, armv7s, arm64

iPhoneSimulator Configuration:i386, x86_64

It seems that the iPhoneSimulator build product is not producing an x86_64 binary based on your question. Check your build configuration - in particular, "Build Active Architectures Only" (ONLY_ACTIVE_ARCH ) should be set to NO. The default is for this to be NO for Release, but YES for debug. If it is YES, only one architecture will be in the build product.