[package] boost/1.88.0: Support wasm64

[stevenwdv]

Description

Now that Conan supports wasm64 (conan-io/conan#17693 / conan-io/conan#18432), support in the Boost recipe may be added as well.

I already described this in conan-io/conan#17693, but I'll copy & update all relevant info below:

When linking against Boost built with the wasm64 architecture, it errors like so:

/home/swdv/emsdk/upstream/emscripten/em++ [...] /home/swdv/.conan2/p/b/boosta13dc00a72eaf/p/lib/libboost_iostreams.a [...] :
wasm-ld: error: /home/swdv/.conan2/p/b/boosta13dc00a72eaf/p/lib/libboost_iostreams.a(file_descriptor.o):
    wasm32 object file can't be linked in wasm64 mode

This seems to be caused by the boost recipe passing the wrong address-model to b2, apparently causing modules to still be compiled as 32-bit:

Boost conan build output

$ conan install --build=missing --profile=wasm64 --requires=boost/1.88.0 --update=boost -o'boost/*:without_stacktrace=True' -o'boost/*:without_process=True'

Requirements
    boost/1.88.0#7bc0bdd001de6abe470e5e41d3c44686:7dafdc010f4fb6cf170e239077aa1f1f608652af
[...]
boost/1.88.0: WARN: Patching user-config.jam
boost/1.88.0: WARN: 
using zlib : 1.3.1 : <include>"/home/swdv/.conan2/p/b/zlib7e2ffcdfd779d/p/include" <search>"/home/swdv/.conan2/p/b/zlib7e2ffcdfd779d/p/lib" <name>z ;                                                                                                                                                               
using bzip2 : 1.0.8 : <include>"/home/swdv/.conan2/p/b/bzip2f0a4614959949/p/include" <search>"/home/swdv/.conan2/p/b/bzip2f0a4614959949/p/lib" <name>bz2 ;                                                                                                                                                          
using "emscripten" :  :  "em++" :                                                                                                                                                                                                                                                                                   
<cxxflags>"-sMEMORY64 -matomics -mbulk-memory -fwasm-exceptions" <cflags>"-sMEMORY64 -matomics -mbulk-memory -fwasm-exceptions"  ;                                                                                                                                                                                  
boost/1.88.0: Cross building, detecting compiler...
boost/1.88.0: Cross building flags: []
boost/1.88.0: WARN: b2 -q numa=on address-model=32 --layout=system --user-config=/home/swdv/.conan2/p/boost83b280b72608f/s/src/tools/build/user-config.jam -sNO_ZLIB=0 -sNO_BZIP2=0 -sNO_LZMA=1 -sNO_ZSTD=1 boost.locale.icu=off --disable-icu boost.locale.iconv=on boost.locale.iconv.lib=libc threading=multi visibility=hidden link=static variant=release --with-atomic --with-charconv --with-chrono --with-cobalt --with-container --with-context --with-contract --with-coroutine --with-date_time --with-exception --with-fiber --with-filesystem --with-graph --with-iostreams --with-json --with-locale --with-log --with-math --with-nowide --with-program_options --with-random --with-regex --with-serialization --with-system --with-test --with-thread --with-timer --with-type_erasure --with-url --with-wave toolset=emscripten cxxstd=2a pch=on linkflags="" cxxflags="-fPIC" install --prefix=/home/swdv/.conan2/p/b/boost7a4eb059c2974/p -j100 --abbreviate-paths -d0 --debug-configuration --build-dir="/home/swdv/.conan2/p/b/boost7a4eb059c2974/b/build-release"                                                                                                                                                                                        
boost/1.88.0: RUN: b2 -q numa=on address-model=32 --layout=system --user-config=/home/swdv/.conan2/p/boost83b280b72608f/s/src/tools/build/user-config.jam -sNO_ZLIB=0 -sNO_BZIP2=0 -sNO_LZMA=1 -sNO_ZSTD=1 boost.locale.icu=off --disable-icu boost.locale.iconv=on boost.locale.iconv.lib=libc threading=multi visibility=hidden link=static variant=release --with-atomic --with-charconv --with-chrono --with-cobalt --with-container --with-context --with-contract --with-coroutine --with-date_time --with-exception --with-fiber --with-filesystem --with-graph --with-iostreams --with-json --with-locale --with-log --with-math --with-nowide --with-program_options --with-random --with-regex --with-serialization --with-system --with-test --with-thread --with-timer --with-type_erasure --with-url --with-wave toolset=emscripten cxxstd=2a pch=on linkflags="" cxxflags="-fPIC" install --prefix=/home/swdv/.conan2/p/b/boost7a4eb059c2974/p -j100 --abbreviate-paths -d0 --debug-configuration --build-dir="/home/swdv/.conan2/p/b/boost7a4eb059c2974/b/build-release"                                                                                                                                                                                         
notice: found boost-build.jam at /home/swdv/.conan2/p/boost83b280b72608f/s/src/boost-build.jam
notice: loading B2 from /home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/build-system.jam
notice: Searching '/etc' '/home/swdv' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/util' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/tools' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/options' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/contrib' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/build' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2' for site-config configuration file 'site-config.jam'.
notice: Configuration file 'site-config.jam' not found in '/etc' '/home/swdv' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/util' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/tools' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/options' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/contrib' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2/build' '/home/swdv/.conan2/p/b20717b8c0763fa/p/bin/.b2'.
notice: Loading explicitly specified user configuration file:
    /home/swdv/.conan2/p/boost83b280b72608f/s/src/tools/build/user-config.jam
notice: Searching '/home/swdv/.conan2/p/boost83b280b72608f/s/src/tools/build' for user-config configuration file 'user-config.jam'.
notice: Loading user-config configuration file 'user-config.jam' from '/home/swdv/.conan2/p/boost83b280b72608f/s/src/tools/build'.
notice: [zlib] Using pre-installed library
notice: [zlib] Condition
notice: [bzip2] Using pre-installed library
notice: [bzip2] Condition
notice: will use 'em++' for emscripten, condition <toolset>emscripten-4.0.11
notice: [emscripten-cfg] <toolset>emscripten-4.0.11 :: emcc :: em++
notice: [emscripten-cfg] <toolset>emscripten-4.0.11 :: archiver :: emar
notice: [emscripten-cfg] <toolset>emscripten-4.0.11 :: nodejs version is 22
node: bad option: --experimental-wasm-threads
notice: [emscripten-cfg] <toolset>emscripten-4.0.11 :: nodejs :: node
Performing configuration checks

    - default address-model    : 64-bit [1]
    - default architecture     : none [1]
    - default address-model    : 64-bit [2]
    - default architecture     : none [2]
    - x86                      : no [3]
    - arm                      : no [3]
    - mips1                    : no [3]
    - power                    : no [3]
    - sparc                    : no [3]
    - cxx11_static_assert      : yes [3]
    - cxx11_variadic_templates : yes [3]
    - cxx11_decltype           : yes [3]
    - GCC libquadmath and __float128 support : no [3]
    - cxx11_hdr_ratio          : yes [3]
    - cxx11_template_aliases   : yes [3]
    - cxx11_char16_t           : yes [3]
    - cxx11_char32_t           : yes [3]
    - cxx20_hdr_concepts       : yes [3]
    - cpp_lib_memory_resource  : yes [3]
    - BOOST_ARCH_WORD_BITS == 0.0.16 : no [3]
    - BOOST_ARCH_WORD_BITS == 0.0.32 : yes [3]
    - BOOST_ARCH_WORD_BITS == 0.0.64 : no [3]
    - BOOST_ARCH_X86           : no [3]
    - BOOST_ARCH_IA64          : no [3]
    - BOOST_ARCH_SPARC         : no [3]
    - BOOST_ARCH_LOONGARCH     : no [3]
    - BOOST_ARCH_MIPS          : no [3]
    - BOOST_ARCH_PARISC        : no [3]
    - BOOST_ARCH_ARM           : no [3]
    - BOOST_ARCH_RISCV         : no [3]
    - BOOST_ARCH_PPC           : no [3]
    - BOOST_ARCH_SYS390        : no [3]
error: No best alternative for /home/swdv/.conan2/p/boost83b280b72608f/s/src/libs/context/build/asm_sources with <abi>sysv <address-model>32 <asynch-exceptions>off <binary-format>elf <boost.beast.allow-deprecated>on <boost.beast.separate-compilation>on <boost.cobalt.executor>any_io_executor <boost.cobalt.pmr>std <boost.locale.iconv.lib>libc <boost.locale.iconv>on <boost.locale.icu>off <closure>off <context-impl>fcontext <coverage>off <cxxstd-dialect>iso <cxxstd>2a <debug-symbols>off <embind>off <exception-handling>on <extern-c-nothrow>off <inlining>full <known-warnings>hide <link-optimization>off <link>static <numa>on <optimization>speed <os>LINUX <pch>on <preserve-test-targets>on <profiling>off <python-debugging>off <relevant>abi <relevant>address-model <relevant>architecture <relevant>binary-format <relevant>toolset <rtti>on <runtime-debugging>off <runtime-link>shared <stdlib>native <strip>off <target-os>none <testing.execute>on <threadapi>pthread <threading>multi <toolset-emscripten:version>4.0.11 <toolset>emscripten <variant>release <vectorize>off <visibility>hidden <warnings-as-errors>off <warnings>on
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>elf <threading>multi <toolset>qcc
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>pe <threading>multi <toolset>msvc
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>mach-o <threading>multi <toolset>gcc
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>pe <threading>multi <toolset>msvc
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>pe <threading>multi <toolset>clang
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>pe <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>loongarch <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>o32 <address-model>32 <architecture>mips <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>o32 <address-model>32 <architecture>mips <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>n64 <address-model>64 <architecture>mips <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>n64 <address-model>64 <architecture>mips <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>mach-o <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>xcoff <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>xcoff <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>mach-o <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>xcoff <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>xcoff <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>xcoff <threading>multi <toolset>xlclang
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>xcoff <threading>multi <toolset>openxl
    no match: <abi>sysv <address-model>32_64 <architecture>power <binary-format>mach-o <threading>multi
    no match: <abi>sysv <address-model>64 <architecture>riscv <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>riscv <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>sparc <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>sparc <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>s390x <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>s390x <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>intel
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>clang
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>clang-win
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>gcc
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>intel
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>msvc
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>embarcadero
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>borland
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>elf <threading>multi <toolset>intel
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>intel
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>clang
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>clang-win
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>gcc
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>intel
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>msvc
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>embarcadero
    no match: <abi>x32 <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>x32 <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>x32 <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>intel
    no match: <abi>sysv <address-model>32_64 <architecture>x86 <binary-format>mach-o <threading>multi
    no match: <abi>sysv <architecture>arm+x86 <binary-format>mach-o <threading>multi
[...]

It seems to build fine, but as can be seen in the b2 command, address-model=32 is passed.

This is caused by _b2_address_model returning 32 in the boost recipe:

conan-center-index/recipes/boost/all/conanfile.py

Lines 1185 to 1189 in 687cd4e

	def _b2_address_model(self):
	if self.settings.arch in ("x86_64", "ppc64", "ppc64le", "mips64", "armv8", "armv8.3", "sparcv9", "s390x", "riscv64"):
	return "64"
	return "32"

(I tried adding boost/*:extra_b2_flags='address-model=64' but it doesn't seem to properly override address-model=32.)

Updating the boost recipe with a case for wasm64 in _b2_address_model would probably solve this. Although, if I can make a suggestion, I also think there should be a centralized function returning the address model, to avoid having to update similar logic in multiple recipes.

Another option might be to look into building Boost with CMake instead of Boost.Build (b2), as vcpkg now does (microsoft/vcpkg#32309).

Package and Environment Details

$ conan version
version: 2.18.1
conan_path: /usr/local/bin/conan
python
  version: 3.12.3
  sys_version: 3.12.3 (main, Jun 18 2025, 17:59:45) [GCC 13.3.0]
  sys_executable: /etc/pipx/venvs/conan/bin/python
  is_frozen: False
  architecture: x86_64
system
  version: #63-Ubuntu SMP PREEMPT_DYNAMIC Tue Apr 15 19:04:15 UTC 2025
  platform: Linux-6.8.0-60-generic-x86_64-with-glibc2.39
  system: Linux
  release: 6.8.0-60-generic
  cpu: x86_64

$ em++ --version
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.11 (d3432e7a2a6585331c94b041973fb16c9f332ce4)
Copyright (C) 2025 the Emscripten authors (see AUTHORS.txt)
This is free and open source software under the MIT license.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

clang version 21.0.0git (https:/github.com/llvm/llvm-project 0f0079c29da4b4d5bbd43dced1db9ad6c6d11008)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/swdv/emsdk/upstream/bin

Conan profile

[settings]
arch=wasm64
build_type=Release
compiler=clang
compiler.cppstd=20
compiler.version=20
os=Emscripten

[conf]
tools.build:compiler_executables={'c':'emcc', 'cpp':'em++'}
tools.cmake.cmaketoolchain:user_toolchain=[ '{{ os.getenv('EMSDK') + '/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake' }}' ]
tools.build:cflags=['-sMEMORY64', '-matomics', '-mbulk-memory', '-fwasm-exceptions']
tools.build:cxxflags=['-sMEMORY64', '-matomics', '-mbulk-memory', '-fwasm-exceptions']

Steps to reproduce

• Install Boost via Conan with the wasm64 profile. You may need to disable some components, see the commandline at the top of the logs above
• Try to link against it in a wasm64 application

[uilianries]

@stevenwdv Hello, and thank you for your suggestion of support wasm64!

Updating the boost recipe with a case for wasm64 in _b2_address_model would probably solve this. Although if I can make a suggestion, I also think there should be a centralized function returning the address model, to avoid having to update similar logic in multiple recipes.

Please feel free to open a PR providing such support if you like, your contribution will be welcome 😄 . Try to follow the PR #27932 as a reference, let's keep it as simple as possible, as the Boost recipe is complex and fragile. There is no risk of multiple recipes because only Boost is using b2.

Another option might be to look into building Boost with CMake instead of Boost. Build (b2), as vcpkg now does (microsoft/vcpkg#32309).

This will not happen in the middle or long term. As you may have noted in the README, the "Note that the officially supported way to build Boost remains with b2" marks b2 as the main build. Also, there is an effort running to bring Boost as a totally modular using only b2 (supported already with CMake). After that support, the recipe maintenance should be much easier. Still, thank you for your suggestion. I myself tried a POC using CMake and it worked fine.

Regards!