Correct iOS architecture names for autotools?

What are the standard architecture names of mobile platforms, namely ARM-based, for autotools?

I've tried to build some C/C++ libs for iOS including arm64, armv7, and iOS simulators (i386 and x86_64), but I always ended up having identical binaries for arm64 and x86_64-simulator, which in turns fails the universal binary build by lipo. I've tried to set the --build and --host switches to one of the following pairs

For arm64: --build=x86_64-apple-darwinuname -r, --host=arm64
For x86_64-simulator: --build=x86_64-apple-darwinuname -r, --host=x86_64-apple-darwinuname -r

To my surprise, running the following script,

## Environments
ScriptDir="$( cd "$( dirname "$0" )" && pwd )"
cd - &> /dev/null

# Exit the build pass if any command returns a non-zero value
#set -o errexit


# Echo commands
set -x

DARWIN=darwin`uname -r`

MIN_SDK_VERSION=8.0

IPHONEOS_SYSROOT=`xcrun --sdk iphoneos --show-sdk-path`
IPHONESIMULATOR_SYSROOT=`xcrun --sdk iphonesimulator --show-sdk-path`

# Verbose clang output
#CLANG_VERBOSE="--verbose"

CC=/usr/bin/clang
CXX=/usr/bin/clang

SILENCED_WARNINGS="-Wno-unused-local-typedef -Wno-unused-function"
STDLIB=libc++

CFLAGS="${CLANG_VERBOSE} ${SILENCED_WARNINGS} -DNDEBUG -g -O0 -pipe -fPIC -fcxx-exceptions"
CXXFLAGS="${CFLAGS} -std=c++11 -stdlib=${STDLIB}"

LDFLAGS="-stdlib=${STDLIB}"
LIBS="-lc++ -lc++abi"

PROTOC=`which protoc`

SOURCE_DIR="$ScriptDir"

PREFIX="$ScriptDir"/_build
if [ -d ${PREFIX} ]
then
    rm -rf "${PREFIX}"
fi
mkdir -p "${PREFIX}/platform" &> /dev/null

## Functions

build_arch() {
  HOST=$1
  ARCH=$2
  PLATFORM_CFLAGS=$3
  PLATFORM_NAME=${ARCH}
  SYSROOT=${IPHONEOS_SYSROOT}

  ARCH_BITS=x86_64
  if [[ $ARCH==armv7 || $ARCH==armv7s ]]; then
    ARCH_BITS=i386
  fi

  CC="${CC}"
  CFLAGS="${CFLAGS} -miphoneos-version-min=${MIN_SDK_VERSION} -arch ${ARCH} -isysroot ${SYSROOT} ${PLATFORM_CFLAGS}" \
  CXX="${CXX}" \
  CXXFLAGS="${CXXFLAGS} -miphoneos-version-min=${MIN_SDK_VERSION} -arch ${ARCH} -isysroot ${SYSROOT}" \
  LDFLAGS="-arch ${ARCH} -miphoneos-version-min=${MIN_SDK_VERSION} ${LDFLAGS}" \
  LIBS="${LIBS}" \
  ./configure \
    --without-gcc \
    --disable-ld-version-script \
    --build=x86_64-apple-${DARWIN} \
    --host=${HOST} \
    --with-protoc=${PROTOC} \
    --disable-shared \
    --prefix=${PREFIX} \
    --exec-prefix=${PREFIX}/platform/${PLATFORM_NAME}

  make -j8
  make install
}

build_simulator() {
  ARCH=$1
  PLATFORM_CFLAGS=$2
  HOST=${ARCH}-apple-${DARWIN}
  PLATFORM_NAME=${ARCH}-simulator
  SYSROOT=${IPHONESIMULATOR_SYSROOT}

  CC="${CC}" \
  CFLAGS="${CFLAGS} -mios-simulator-version-min=${MIN_SDK_VERSION} -arch ${ARCH} -isysroot ${SYSROOT} ${PLATFORM_CFLAGS}" \
  CXX="${CXX}" \
  CXXFLAGS="${CXXFLAGS} -mios-simulator-version-min=${MIN_SDK_VERSION} -arch ${ARCH} -isysroot ${SYSROOT}" \
  LDFLAGS="-arch ${ARCH} -mios-simulator-version-min=${MIN_SDK_VERSION} ${LDFLAGS}" \
  LIBS="${LIBS}" \
  ./configure \
    --without-gcc \
    --disable-ld-version-script \
    --build=x86_64-apple-${DARWIN} \
    --host=${HOST} \
    --with-protoc=${PROTOC} \
    --disable-shared \
    --prefix=${PREFIX} \
    --exec-prefix=${PREFIX}/platform/${PLATFORM_NAME}

  make -j8
  make install
}


build_fat_lib() {
  OUT=${PREFIX}/universal
  mkdir -p ${OUT}

  PLATFORM_ROOT=${PREFIX}/platform
  LIPO=lipo

  LIB=libprotobuf.a
  ${LIPO} ${PLATFORM_ROOT}/arm64/lib/${LIB} \
          ${PLATFORM_ROOT}/x86_64-simulator/lib/${LIB} \
          -create \
          -output ${OUT}/${LIB}

  LIB_LITE=libprotobuf-lite.a
  ${LIPO} ${PLATFORM_ROOT}/arm64/lib/${LIB_LITE} \
          ${PLATFORM_ROOT}/x86_64-simulator/lib/${LIB_LITE} \
          -create \
          -output ${OUT}/${LIB_LITE}
}

## Build pass

cd ${SOURCE_DIR}

./autogen.sh

build_simulator x86_64 "-fembed-bitcode"

build_arch arm arm64 "-fembed-bitcode"

build_fat_lib

echo DONE!

, I end up getting complaints from lipo:

+ lipo /path/to/protobuf/_build/platform/arm64/lib/libprotobuf.a /path/to/protobuf/_build/platform/x86_64-simulator/lib/libprotobuf.a -create -output /path/to/protobuf/_build/universal/libprotobuf.a

fatal error: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/lipo: /path/to/protobuf/_build/platform/arm64/lib/libprotobuf.a and /path/to/protobuf/_build/platform/x86_64-simulator/lib/libprotobuf.a have the same architectures (x86_64) and can't be in the same fat output file

My first impression is that I'm misusing architecture names, and I don't know where to get the standard names. Is that it?

Solution

Solved it myself.

It turns out that the real problem is not a wrong arch triplet, but an inappropriate compiler executable assigned to CC/CXX. You gotta use

SDK="iphoneos"
export CC=$(xcrun --find --sdk "${SDK}" clang)
export CXX=$(xcrun --find --sdk "${SDK}" clang++)
export CPP=$(xcrun --find --sdk "${SDK}" cpp)

GOTCHA #1

config.guess as suggested by @JohnBolinger will always return

x86_64-apple-darwin18.7.0

This leads to the wrong x86_64 build that I had before.

GOTCHA #2

Observe the Xcode build log and you may find -target arm64-apple-ios13.1 as a Clang option, not to be confused with the autotool configure option --target. This one is useless either, unfortunately.