Build fails for target aarch64-unknown-linux-musl

[ifreund]

I am currently in the process of packaging wasmtime for void linux, a distribution which supports multiple architectures and musl as an alternative to glibc.

Reading the following code, it looks like wasmtime is intended to support aarch64 on linux.

wasmtime/crates/runtime/src/traphandlers.rs

Lines 158 to 172 in 0387169

	if #[cfg(all(target_os = "linux", target_arch = "x86_64"))] {
	let cx = &*(cx as *const libc::ucontext_t);
	cx.uc_mcontext.gregs[libc::REG_RIP as usize] as *const u8
	} else if #[cfg(all(target_os = "linux", target_arch = "x86"))] {
	let cx = &*(cx as *const libc::ucontext_t);
	cx.uc_mcontext.gregs[libc::REG_EIP as usize] as *const u8
	} else if #[cfg(all(any(target_os = "linux", target_os = "android"), target_arch = "aarch64"))] {
	let cx = &*(cx as *const libc::ucontext_t);
	cx.uc_mcontext.pc as *const u8
	} else if #[cfg(target_os = "macos")] {
	let cx = &*(cx as *const libc::ucontext_t);
	(*cx.uc_mcontext).__ss.__rip as *const u8
	} else {
	compile_error!("unsupported platform");
	}

It builds fine for aarch64-unknown-linux-gnu but fails for aarch64-unknown-linux-musl with the following error:

error[E0412]: cannot find type `ucontext_t` in crate `libc`

   --> crates/runtime/src/traphandlers.rs:165:52
    |
165 |                     let cx = &*(cx as *const libc::ucontext_t);
    |                                                    ^^^^^^^^^^ not found in `libc`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0412`.
error: could not compile `wasmtime-runtime`.

Building for x86_64-unknown-linux-musl works fine.

This failure occurred with rust 1.44.1 and wasmtime 0.19.0

[bjorn3]

libc misses ucontext_t on aarch64-unknown-linux-musl.

glibc: https://github.com/rust-lang/libc/blob/035a4809428d319e72ff1aaae5c5335f18623836/src/unix/linux_like/linux/gnu/b64/aarch64/align.rs
musl: https://github.com/rust-lang/libc/blob/035a4809428d319e72ff1aaae5c5335f18623836/src/unix/linux_like/linux/musl/b64/aarch64/align.rs

[pmengelbert]

I see that the issue has been patched and is resolved if I upgrade to the latest version of the libc crate, but then I come across this issue here:

error[E0609]: no field `pc` on type `libc::mcontext_t`
   --> crates/runtime/src/traphandlers.rs:166:36
    |
166 |                     cx.uc_mcontext.pc as *const u8
    |                                    ^^ unknown field

error: aborting due to previous error

Like @ifreund, building for the x86_64-unknown-linux-musl target works just fine. Any pointers on where to look? Thanks

[bjorn3]

On aarch64-unknown-linux-musl libc doesn't expose any fields for mcontext_t: https://github.com/rust-lang/libc/blob/c9ff3e9b4e49b1a1c8482fc409177615dce6b84c/src/unix/linux_like/linux/musl/b64/aarch64/align.rs#L19 This will require a change to the libc crate.

[jiayihu]

I'm having the same issue of @pmengelbert, is there any way to workaround for now? For instance fork libc and apply some patch. I'd test and open the PR myself if anyone can point me what to write. Should I just copy over this lines?

https://github.com/rust-lang/libc/blob/c9ff3e9b4e49b1a1c8482fc409177615dce6b84c/src/unix/linux_like/linux/gnu/b64/aarch64/align.rs#L19-L27

[lu-zero]

something along https://gist.github.com/lu-zero/e770b7c3c01277a7ccac51b2af692632 should fix it.