When attempting to cross-compile boost 1.69.0 for iOS (with clang) and using external dependencies it fails to compile because when it tests to see if the dependencies are valid, it fails to compile the test program correctly due to it attempting to add incorrect linker flags. I tried modifying the boost.build to not add those flags but it seemed to unravel a rat's nest of issues (attempting to link with librt even though its for iOS, compiled the test program for x86 and not arm, etc.., etc..) The error I keep getting is... ld: unknown option: --start-group Thank you for your help. I am using the following b2 options.. ./b2 --prefix=/Users/afalls/delete-me/build-boost/install/ \ --build-dir=/Users/afalls/delete-me/build-boost/build/ \ --user-config=/Users/afalls/delete-me/build-boost/ios-config.jam \ --with-math \ --with-wave \ --with-container \ --with-contract \ --with-exception \ --with-graph \ --with-iostreams \ --with-locale \ --with-log \ --with-program_options \ --with-random \ --with-regex \ --with-mpi \ --with-serialization \ --with-coroutine \ --with-fiber \ --with-context \ --with-timer \ --with-thread \ --with-chrono \ --with-date_time \ --with-atomic \ --with-filesystem \ --with-system \ --with-graph_parallel \ --with-stacktrace \ --with-test \ --with-type_erasure \ -q \ -j 16 \ toolset=clang \ threading=multi \ architecture=arm \ abi=aapcs \ binary-format=mach-o \ address-model=64 \ cxxflags="${IOS_CXXFLAGS}" \ cflags="${IOS_CFLAGS}" \ target-os=iphone \ link=static \ variant=release \ define=_LITTLE_ENDIAN \ install My user-config.jam file is below... import os ; using clang : : /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -arch arm64 -DBOOST_AC_USE_PTHREADS -DBOOST_SP_USE_PTHREADS -Wno-unused-local-typedef -Wno-nullability-completeness -miphoneos-version-min=9.0 -fPIC : <stripper> <root>/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk <architecture>arm <target-os>iphone <include>/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include ; using zlib : 1.2.11 : <include>/Users/afalls/.conan/data/zlib/1.2.11/channel/niantic/package/d522642044ded35b1d89ab2201a41e2c5d74a0b0/include <search>/Users/afalls/.conan/data/zlib/1.2.11/channel/niantic/package/d522642044ded35b1d89ab2201a41e2c5d74a0b0/lib <name>z ; using lzma : 5.2.4 : <include>/Users/afalls/.conan/data/xz_utils/5.2.4/channel/niantic/package/d522642044ded35b1d89ab2201a41e2c5d74a0b0/include <search>/Users/afalls/.conan/data/xz_utils/5.2.4/channel/niantic/package/d522642044ded35b1d89ab2201a41e2c5d74a0b0/lib <name>lzma ; using bzip2 : 1.0.8 : <include>/Users/afalls/.conan/data/bzip2/1.0.8/channel/niantic/package/d522642044ded35b1d89ab2201a41e2c5d74a0b0/include <search>/Users/afalls/.conan/data/bzip2/1.0.8/channel/niantic/package/d522642044ded35b1d89ab2201a41e2c5d74a0b0/lib <name>bz2 ; using zstd : 1.4.4 : <include>/Users/afalls/.conan/data/zstd/1.4.4/channel/niantic/package/d522642044ded35b1d89ab2201a41e2c5d74a0b0/include <search>/Users/afalls/.conan/data/zstd/1.4.4/channel/niantic/package/d522642044ded35b1d89ab2201a41e2c5d74a0b0/lib <name>zstd ;