I suggest we build cxa_demangle standalone into js. Then we would include it in emcc if the user asks for this option. Including could be as a pre-js for example. This would fix the first two issues here.

Regarding the loading of the map file - are source maps text? Then we can do a sync xhr to load them the first time.

Regarding node, we can file a bug. Working in the browser is a great first step.

I now had a go at building the cxa_demangle.cpp to a .js library. I first tried (in emscripten root directory of this branch):

em++ -s SIDE_MODULE=1 system\lib\libcxxabi\src\cxa_demangle.cpp -Isystem\lib\libcxxabi\include -o lib_cxa_demangle.js
em++ -g tests\emscripten_log\emscripten_log.cpp --pre-js lib_cxa_demangle.js -o emscripten_log.js
node emscripten_log.js

but I suppose --pre-js'ing side modules is not a supported machinery. The result in running that code is that the function ___cxa_demangle is not seen by the main code, since it's inside an unnamed function().

Second I tried to follow the linking guide directly with:

em++ -s SIDE_MODULE=1 system\lib\libcxxabi\src\cxa_demangle.cpp -Isystem\lib\libcxxabi\include -o lib_cxa_demangle.js
em++ -s MAIN_MODULE=1 -g tests\emscripten_log\emscripten_log.cpp -o emscripten_log.js
emlink emscripten_log.js lib_cxa_demangle.js out.js

but that gives an error

Main module: emscripten_log.js
Side module: lib_cxa_demangle.js
Output: out.js
Traceback (most recent call last):
  File "C:\Projects\emsdk_uqm\emscripten\incoming\\emlink.py", line 25, in <modu
le>
    main = AsmModule(main)
  File "C:\Projects\emsdk_uqm\emscripten\incoming\tools\asm_module.py", line 55,
 in __init__
    self.tables = self.parse_tables(self.tables_js)
  File "C:\Projects\emsdk_uqm\emscripten\incoming\tools\asm_module.py", line 243
, in parse_tables
    part = part.split('var ')[1]
IndexError: list index out of range

I added a "if 'var ' not in part: continue" to asm_module.py to try to get past of this, but then I got another error with

Main module: emscripten_log.js
Side module: lib_cxa_demangle.js
Output: out.js
main = ['function() { // Emscripten wrappe']
Traceback (most recent call last):
  File "C:\Projects\emsdk_uqm\emscripten\incoming\\emlink.py", line 28, in <modu
le>
    side.relocate_into(main)
  File "C:\Projects\emsdk_uqm\emscripten\incoming\tools\asm_module.py", line 130
, in relocate_into
    main.tables[table] = self.merge_tables(table, main.tables.get(table), data,
replacements, f_bases, f_sizes)
  File "C:\Projects\emsdk_uqm\emscripten\incoming\tools\asm_module.py", line 260
, in merge_tables
    assert len(main) % 2 == 0
AssertionError

which looks like the code gets confused by comments or whitespace? @kripken, could you take a peek when you have time?

emlink only works with asm.js code...

Yes, emlink is only for asm.js code - we should error on MAIN_MODULE and SIDE_MODULE if asm is not enabled, I'll add that now.

Reading the docs on name mangling, it looks pretty trivial: http://en.wikipedia.org/wiki/Name_mangling#Complex_example

Basically _Z[N] then a list of number and a string of that length, then the parameter types - which I'm not sure we need here (N means nested, so a class or namespace). Seems pretty trivial to write our own demangler in 20 lines or so of code, and avoid the complexity of needing to include cxa_demangle etc.

See last commits on adding stackTrace() and automatic stack demangling on abort().

I wonder if we shouldn't add a printf option for the stack. So printf("%S - blah blah\n") would print out the stack + the text? Or maybe better to not modify printf and keep it posix compliant, and add a function like you did here?

I'm trying to port some code that relies on __cxa_demangle (among other cxxabi features -- see this thread https://groups.google.com/forum/#!topic/emscripten-discuss/nzlKaLNQFrE).

Should I follow the steps outlined by @juj in the first comment above?

That worked for me, though I'm still curious if I should officially integrate this step into our build system, or if a better solution is available.

@jcowles : Alon did great work in supporting demangle() from native JS side. It's in my todo list to convert to using that, which will solve the inconveniency with the two first bullet points in the PR message. To get callstacks, the third and fourth bullet points still stand.

Even after this pull request is merged, nothing should break if you already did the same manually in your own codebase. Sorry for not giving this much attention in a while, there's been a lot of higher priority work in the meanwhile.

Ok, updated this pull request to latest. Thanks azakai for the handwritten demangler, it works beautifully now!

Updated the PR. Also added the bug number to the source.