fiber: fails to build on 32-bit x86 and arm

[jbeich]

Regresed by #5459 (missed x86.rs and arm.rs). Found while packaging Veloren.

$ cargo build --target i686-unknown-linux-gnu
[...]
error[E0432]: unresolved import `wasmtime_asm_macros::asm_sym`
  --> crates/fiber/src/unix/x86.rs:13:37
   |
13 | use wasmtime_asm_macros::{asm_func, asm_sym};
   |                                     ^^^^^^^ no `asm_sym` in the root

For more information about this error, try `rustc --explain E0432`.
error: could not compile `wasmtime-fiber` (lib) due to previous error

[bjorn3]

Wasmtime doesn't work on 32bit x86 and arm32. It is not just a missing fiber implementation (that would be easy to fix), but also missing backends for both architectures in Cranelift, which is a lot harder to fix. See #1173 and #1980.

[alexcrichton]

To add more on what @bjorn3 already mentioned, can you clarify what you mean by regressed by #5459? Wasmtime/Cranelift haven't had support for x86 and arm in quite some time so that PR shouldn't have regressed anything "in the large". If, however, you only need the wasmtime-fiber crate and nothing else then I can see that PR regressing the support there. Do you only need the wasmtime-fiber crate? Given the commit you linked it seems like you're packaging all of Wasmtime so while it doesn't seem like this is the case I wanted to ask to be sure. (if you need all of Wasmtime I'll close this in favor of the issues that @bjorn3 linked tracking 32-bit support)

[jbeich]

Indeed. I've got confused by the cruft i.e., x86 and arm support in wasmtime-fiber which is trivial to fix by removing unused asm_sym. Veloren then failed in wasmtime-runtime due to missing assembly but otherwise built fine (I've stubbed the assembly using x86_64 as example to check for more errors but didn't find any).