Example by cross-compiling libiconv

Build a standalone toolchain

When compiling using Automake you'll need a standalone toolchain that embodies one target architecture and a specific platform revision. The procedure is outlined in the following script.

generate-standalone.sh

#!/bin/bash 

ANDROID_NDK_DIR=/opt/android-ndk-r13b
ANDROID_API=19
ANDROID_STL=gnustl
INSTALL_PREFIX=/opt/standalone-r13b
declare -a COMPILE_ARCHITECTURES=("arm" "x86")

pushd ${ANDROID_NDK_DIR}
for ARCH in "${COMPILE_ARCHITECTURES[@]}"
do
    INSTALL_DIR=${INSTALL_PREFIX}-${ARCH}
    build/tools/make_standalone_toolchain.py \
        --arch ${ARCH} \
        --api ${ANDROID_API} \
        --stl ${ANDROID_STL} \
        --install-dir ${INSTALL_DIR}
done
popd

Replace config.sub and config.guess

On some older projects you'll find that the config.guess and config.sub files won't recognize the Android NDK toolchain so you'll need to grab a newer one from automake. In this project I copied the files from Automake 1.15 and just overwrote the ones in the libiconv project.

Compiling for 3 architectures

Note: I haven't compiled 64-bit targets in this example. I would need to raise the Android API to 21 to add ARM64 and x86_64.

ANDROID_NDK_DIR=/opt/standalone-r13b
LIBICONV_INSTALL_DIR=${HOME}/Development/libiconv

declare -a COMPILE_ARCHITECTURES=("arm" "armv7a" "x86")
SAVED_PATH="${PATH}"
for ARCH in "${COMPILE_ARCHITECTURES[@]}"
do
    COMPILER_GROUP=""
    COMPILER_PREFIX=""
    case ${ARCH} in
        "arm" )
            COMPILER_GROUP=arm
            ;;
        "armv7a" )
            COMPILER_GROUP=arm
            ;;
        "x86" )
            COMPILER_GROUP=x86
            ;;
    esac

    export ANDROID_NDK_ROOT="${ANDROID_NDK_DIR}-${COMPILER_GROUP}"

    ANDROID_NDK_BIN="${ANDROID_NDK_ROOT}/bin"
    ANDROID_SYSROOT_DIR="${ANDROID_NDK_ROOT}/sysroot"

    export PATH="${ANDROID_NDK_BIN}:${SAVED_PATH}"

    export CFLAGS="--sysroot=${ANDROID_SYSROOT_DIR}"
    export CXXFLAGS="--sysroot=${ANDROID_SYSROOT_DIR}"
    case ${ARCH} in
        "arm" )
            ABI_NAME=armeabi
            COMPILER_PREFIX=arm-linux-androideabi
            ;;
        "armv7a" )
            ABI_NAME=armeabi-v7a
            COMPILER_PREFIX=arm-linux-androideabi
            CFLAGS="${CFLAGS} -march=armv7-a -mfpu=neon -mfloat-abi=softfp" 
            ;;
        "x86" )
            ABI_NAME=x86
            COMPILER_PREFIX=i686-linux-android
            ;;
    esac


    export CC=${ANDROID_NDK_BIN}/${COMPILER_PREFIX}-gcc
    export CPP=${ANDROID_NDK_BIN}/${COMPILER_PREFIX}-cpp
    export CXX=${ANDROID_NDK_BIN}/${COMPILER_PREFIX}-g++
    export LD=${ANDROID_NDK_BIN}/${COMPILER_PREFIX}-ld
    export AR=${ANDROID_NDK_BIN}/${COMPILER_PREFIX}-ar
    export RANLIB=${ANDROID_NDK_BIN}/${COMPILER_PREFIX}-ranlib
    export STRIP=${ANDROID_NDK_BIN}/${COMPILER_PREFIX}-strip

   echo "---- Compiling for ${ARCH}"
   ./configure --host="${COMPILER_PREFIX}" --prefix="${LIBICONV_INSTALL_DIR}/${ABI_NAME}"
   make clean
   make -j4
   make install
done

export PATH="${SAVED_PATH}"

Validating the libraries target the desired architecture

From the NDK you can find arm-linux-androideabi-readelf to determine if for example I'm using Thumb-1 or Thumb-2 instructions in armeabi and armeabi-v7a respectively.

arm-linux-androideabi-readelf -A libiconv.so.2.5.1.so

armeabi

Attribute Section: aeabi
File Attributes
  Tag_CPU_name: "5TE"
  Tag_CPU_arch: v5TE
  Tag_ARM_ISA_use: Yes
  Tag_THUMB_ISA_use: Thumb-1
  Tag_FP_arch: VFPv2
  Tag_ABI_PCS_wchar_t: 4
  Tag_ABI_FP_denormal: Needed
  Tag_ABI_FP_exceptions: Needed
  Tag_ABI_FP_number_model: IEEE 754
  Tag_ABI_align_needed: 8-byte
  Tag_ABI_enum_size: int
  Tag_ABI_optimization_goals: Aggressive Speed

armeabi-v7a

Attribute Section: aeabi
File Attributes
  Tag_CPU_name: "ARM v7"
  Tag_CPU_arch: v7
  Tag_CPU_arch_profile: Application
  Tag_ARM_ISA_use: Yes
  Tag_THUMB_ISA_use: Thumb-2
  Tag_FP_arch: VFPv3
  Tag_Advanced_SIMD_arch: NEONv1
  Tag_ABI_PCS_wchar_t: 4
  Tag_ABI_FP_denormal: Needed
  Tag_ABI_FP_exceptions: Needed
  Tag_ABI_FP_number_model: IEEE 754
  Tag_ABI_align_needed: 8-byte
  Tag_ABI_enum_size: int
  Tag_ABI_HardFP_use: Deprecated
  Tag_ABI_optimization_goals: Aggressive Speed
  Tag_CPU_unaligned_access: v6