This commit collects together some LLVM PRs, some changes in the build
configuration here, and some thoughts from #565 and related issues.
Specifically the changes here are:
* The patch for llvm/llvm-project#168449 is updated to its upstream
(unlanded) form.
* Patches for the (landed) llvm/llvm-project#185770 and
llvm/llvm-project#185775 are added.
* The `WASI_SDK_EXCEPTIONS` configuration is now either `ON`, `OFF`, or
`DUAL`. The default depends on the version of Clang in use, where
23.0.0+ (which isn't released officially yet) will be `DUAL` and
otherwise it's `OFF`. CI for our custom-built patched toolchain defaults
to `DUAL`.
* In `DUAL` mode libcxx is built twice into two different directories,
once with exceptions and once without. This is supported by LLVM patches
and means that Clang will select the right set of libraries based on
compiler flags.
The end result here is that the produced toolchain from this repository,
by default, supports C++ exceptions. Additionally if exceptions-related
flags are not passed then the final binary will not use C++ exceptions
nor require the wasm exception-handling proposal.
There's still follow-up work from #565, such as:
* Subjectively it feels wordy to pass `-fwasm-exceptions` vs
`-fexceptions`.
* Personally I think `-mllvm -wasm-use-legacy-eh=false` should become
the default upstream.
* Subjectively I don't think that `-lunwind` should be necessary and it
should be injected automatically with `-fwasm-exceptions` (or
`-fexceptions`).
* Shared libraries for exceptions remain disabled due to build errors I
do not personally know how to resolve.
I'll file follow-up issues for these once this has landed since they're
more minor compared to the main body of "anything works".
Closes#334Closes#565
---------
Co-authored-by: Joel Dice <joel.dice@akamai.com>
> **Note**: this PR is me weaving together the work of many others. For
example @yerzham's and @cpetig's work on #565 pretty much shaped this
PR. Thank you!
This commit adds initial configuration support for building wasi-sdk
with support for C++ exceptions in WebAssembly. A small test is included
which is exercised in CI at this time, but otherwise this does not
update CI to actually ship sdk builds with C++ exceptions enabled.
Instead the intention here is to make it easier to test builds with
support for C++ exceptions and centralize planning/development around
this.
The goal here is to get things compiling to the point that applications
can be compiled. I haven't thoroughly tested C++ exceptions and as
evident in this PR it still requires changes in LLVM. Some small logic
is added here to apply a `*.patch` file to LLVM to avoid needing a new
submodule fork or waiting for upstream changes. The intention is that
this `*.patch` is short-lived once the changes are officially merged
into LLVM itself.
The `*.patch` included here contains llvm/llvm-project#168449 as well as
another minor edit I found was necessary to get things compiling
locally. Given the discussion on that PR it looks like once LLVM is
updated with that merged the extra part of the `*.patch` won't be
necessary.
This PR notably does not enable shared libraries when exceptions are
enabled. I don't know enough about how things are supposed to work to be
able to fully diagnose the compilation errors I'm seeing if shared
libraries are enabled. This is something I'd hope would be fixed before
actually shipping exceptions support.
This PR then additionally folds in [this gist][gist] for various bits of
build logic to this repository itself.
Finally, this PR includes some documentation about the current status of
exceptions and links to various tracking issues too.
[gist]: https://gist.github.com/yerzham/302efcec6a2e82c1e8de4aed576ea29d
Alex Crichton