I finally managed to compile the needed libraries with emscripten. Here are the steps I followed.

Changes in emscripten

Edit system/include/libcxx/climits to add the following definitions (see http://github.com/kripken/emscripten/issues/531):

#ifndef CHAR_BIT# define CHAR_BIT __CHAR_BIT__#endif#ifndef CHAR_MIN# define CHAR_MIN (-128)#endif#ifndef CHAR_MAX# define CHAR_MAX 127#endif#ifndef SCHAR_MIN# define SCHAR_MIN (-128)#endif#ifndef SCHAR_MAX# define SCHAR_MAX 127#endif#ifndef UCHAR_MAX# define UCHAR_MAX 255#endif#ifndef SHRT_MIN# define SHRT_MIN (-32767-1)#endif#ifndef SHRT_MAX# define SHRT_MAX 32767#endif#ifndef USHRT_MAX# define USHRT_MAX 65535#endif#ifndef INT_MAX# define INT_MAX __INT_MAX__#endif#ifndef INT_MIN# define INT_MIN (-INT_MAX-1)# define INT_MIN (-INT_MAX-1)#endif#ifndef UINT_MAX# define UINT_MAX (INT_MAX * 2U + 1)#endif#ifndef LONG_MAX# define LONG_MAX __LONG_MAX__#endif#ifndef LONG_MIN# define LONG_MIN (-LONG_MAX-1)#endif#ifndef ULONG_MAX# define ULONG_MAX (LONG_MAX * 2UL + 1)#endif

Add the following line in system/include/libcxx/cwchar

#include <cstdio>

Compiling Boost as shared libraries

As suggested by npclaudiu, bootstrap the library using the gcc toolkit. Then edit project-config.jam to configure the compiler and replace:

# Compiler configuration. This definition will be used unless# you already have defined some toolsets in your user-config.jam# file.if ! gcc in [ feature.values <toolset> ]{    using gcc ;}

with

# Compiler configuration. This definition will be used unless# you already have defined some toolsets in your user-config.jam# file.if ! gcc in [ feature.values <toolset> ]{    using gcc : : "/full/path/to/emscripten/em++" ;}

Force BOOST_HAS_SCHER_YIELD in boost/config/posix_features.hpp, around the line 67.

Then compile the libraries: ./b2 thread regex filesystem signals system

Compiling Boost as static libraries

Do all the above steps, then edit tools/build/v2/tools/gcc.jam and replace:

toolset.flags gcc.archive .AR $(condition) : $(archiver[1]) ;

with

toolset.flags gcc.archive .AR $(condition) : "/full/path/to/emscripten/emar" ;

and

toolset.flags gcc.archive .RANLIB $(condition) : $(ranlib[1]) ;

with

toolset.flags gcc.archive .RANLIB $(condition) :  "/full/path/to/emscripten/emranlib" ;

Compile the libraries: ./b2 link=static variant=release threading=single runtime-link=static thread signals system filesystem regex

For the record, Boost now includes an "emscripten" toolset, which (in my experience) makes the process described above unnecessary.

To use, boostrap boost as normal, then compile with b2 (or bjam) like so:

b2 toolset=emscripten 

In newer versions of emscripten, you can simply add Boost libraries using ports. It's now as easy as adding this flag to the compiler and linker:-s USE_BOOST_HEADERS=1

If you're using CMake, you can add the flag like this:

set_target_properties(your_targets_name_here PROPERTIES COMPILE_FLAGS "-s USE_BOOST_HEADERS=1" LINK_FLAGS "-s USE_BOOST_HEADERS=1")

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