This commit updates how the linker is invoked on WebAssembly targets
(all of them) to avoid passing the `--allow-undefined` flag to the
linker. Historically, if I remember this correctly, when `wasm-ld` was
first integrated this was practically required because at the time it
was otherwise impossible to import a function from the host into a wasm
binary. Or, at least, I'm pretty sure that was why this was added.
At the time, as the documentation around this option indicates, it was
known that this was going to be a hazard. This doesn't match behavior on
native, for example, and can easily paper over what should be a linker
error with some sort of other obscure runtime error. An example is that
this program currently compiles and links, it just prints null:
unsafe extern "C" {
static nonexistent: u8;
}
fn main() {
println!("{:?}", &raw const nonexistent);
}
This can easily lead to mistakes like rust-lang/libc/4880 and defer what
should be a compile-time link error to weird or unusual behavior at link
time. Additionally, in the intervening time since `wasm-ld` was first
introduced here, lots has changed and notably this program works as
expected:
#[link(wasm_import_module = "host")]
unsafe extern "C" {
fn foo();
}
fn main() {
unsafe {
foo();
}
}
Notably this continues to compile without error and the final wasm
binary indeed has an imported function from the host. What this change
means, however, is that this program:
unsafe extern "C" {
fn foo();
}
fn main() {
unsafe {
foo();
}
}
this currently compiles successfully and emits an import from the `env`
module. After this change, however, this will fail to compile with a
link error stating that the `foo` symbol is not defined.
This commit rewrites a number of `run-make` tests centered around wasm
to instead use `rmake.rs` and additionally use the `wasm32-wasip1`
target instead of `wasm32-unknown-unknown`. Testing no longer requires
Node.js and additionally uses the `wasmparser` crate from crates.io to
parse outputs and power assertions.
apparently I missed some tests in the last commit. Rather than having
dozens of tests use the long version, use the short version in
`run-make` and the long version in `run-make-fulldeps` (which is now
only three tests)
Alex Crichton