dtolnay
cxx: implement slice support for nostd
OVERVIEW:
This patch adds experimental support for us to use slices in a nostd/freestanding environment, aim is to run c++ <=> cxx-rs <=> rust on a baremental target environment and use slices, with the intention of supporting more features later.
CFG
In the application Cargo.toml file, the following feature cfgs are required:
[dependencies]
cxx = { ... , default-features = false }
[build-dependencies]
cxx-build = { ... , default-features = false }
Then build with:
RUSTFLAGS='--cfg cxx_experimental_no_alloc' cargo build
Build Notes
and in the particular .cpp file you may need to declare the following
void __assert_func (const char *__a, int, const char *__b, const char *__c) {
while (true) {}
}
void *__gxx_personality_v0;
FUNCTIONALITY:
Currently, this only supports slices (outside of trivial features).
TESTING:
Tested by compiling:
-
cargo test (run existing tests)
-
cxx/demo/ running it.
-
compiling with a arm toolchain setup with cmake/corrosion and running the binary on QEMU arm with basic logic assertions [1].
Current testing has been done in the direction of C++ -> Rust with a simple callback test to C++. A simple test setup can be seen here [2].
TODO:
-
Get features such as
Results<Ok, Err>working. -
When we build for the none
stdcase (nodefault-features), instead of creating a symlink to the originalcxx.hfile, we copy it over and define the macro to disable stdlib dependencies. Perhaps there's a better way to do this?
NOTES:
By default, all the standard features are enabled gaurded by the #ifndef CXXBRIDGE1_RUST_STD, so this shoudn't break anything.
[1] https://github.com/twilfredo/qemu_misc/tree/master/bm_arm [2] https://github.com/twilfredo/qemu_misc/blob/master/bm_arm/main.cpp
Signed-off-by: Wilfred Mallawa [email protected]
