> "how do I set the default architecture when building boost?"
>

address-model=64 architecture=x86

Indeed, using these two commands as

./b2 address-model=64 architecture=x86

changes both of those properties as expected. however, if I use them in conjunction with toolset=emscripten, the problem I originally asked about persists:

./b2 toolset=emscripten address-model=64 architecture=x86

Performing configuration checks

- default address-model : 32-bit

- default architecture : none

Building the Boost C++ Libraries.

- symlinks supported : yes

error: No best alternative for libs/context/build/asm_sources

next alternative: required properties: <abi>aapcs <address-model>32 <architecture>arm <binary-format>elf <threading>multi <toolset>clang

not matched

next alternative: required properties: <abi>aapcs <address-model>32 <architecture>arm <binary-format>elf <threading>multi <toolset>gcc

... [more similar alternatives omitted for brevity --dab]

- C++11 mutex : no

- lockfree boost::atomic_flag : yes

- Boost.Config Feature Check: cxx11_hdr_tuple : no

- Boost.Config Feature Check: cxx11_lambdas : no

- Boost.Config Feature Check: cxx11_noexcept : no

- Boost.Config Feature Check: cxx11_nullptr : no

- Boost.Config Feature Check: cxx11_rvalue_references : no

- Boost.Config Feature Check: cxx11_template_aliases : no

- Boost.Config Feature Check: cxx11_thread_local : no

- Boost.Config Feature Check: cxx11_variadic_templates : no

- Boost.Config Feature Check: cxx11_auto_declarations : no

- Boost.Config Feature Check: cxx11_constexpr : no

- Boost.Config Feature Check: cxx11_defaulted_functions : no

- Boost.Config Feature Check: cxx11_final : no

- Boost.Config Feature Check: cxx11_hdr_mutex : no

Error: ambiguity found when searching for best transformation

Trying to produce type 'SEARCHED_LIB' from:

Generators that succeeded:

- searched-lib-generator

- emscripten.searched-lib-generator

First generator produced:

- { %.no-action-icudata.SEARCHED_LIB }

Second generator produced:

- { %.no-action-icudata.SEARCHED_LIB }

to renew focus, the problem I am trying to solve is the last part there, ambiguity when searching for best transformation. it goes away if i disable icu, but it just yields another similar error. it was suggested that I need to provide the default architecture to solve the problem, but the way suggested to do that so far have not worked. your help is appreciated!

Danielle Brake