wasmtime / issue #11506 Compiling wasmtime for the embedd... · git-wasmtime

commit b1bf88344905ac4813ec4a7bce58e475678b175f
Author: Alex Crichton <alex@alexcrichton.com>
Date:   Fri Aug 22 17:15:17 2025 -0700

    wip

diff --git a/examples/min-platform/embedding/src/lib.rs b/examples/min-platform/embedding/src/lib.rs
index 460ea5d2c8..9448c3785e 100644
--- a/examples/min-platform/embedding/src/lib.rs
+++ b/examples/min-platform/embedding/src/lib.rs
@@ -4,7 +4,7 @@
 extern crate alloc;

 use alloc::string::ToString;
-use anyhow::Result;
+use anyhow::{Result, ensure};
 use core::ptr;
 use wasmtime::{Engine, Instance, Linker, Module, Store};

@@ -29,6 +29,8 @@ pub unsafe extern "C" fn run(
     simple_add_size: usize,
     simple_host_fn_module: *const u8,
     simple_host_fn_size: usize,
+    simple_floats_module: *const u8,
+    simple_floats_size: usize,
 ) -> usize {
     unsafe {
         let buf = core::slice::from_raw_parts_mut(error_buf, error_size);
@@ -36,7 +38,8 @@ pub unsafe extern "C" fn run(
         let simple_add = core::slice::from_raw_parts(simple_add_module, simple_add_size);
         let simple_host_fn =
             core::slice::from_raw_parts(simple_host_fn_module, simple_host_fn_size);
-        match run_result(smoke, simple_add, simple_host_fn) {
+        let simple_floats = core::slice::from_raw_parts(simple_floats_module, simple_floats_size);
+        match run_result(smoke, simple_add, simple_host_fn, simple_floats) {
             Ok(()) => 0,
             Err(e) => {
                 let msg = format!("{e:?}");
@@ -52,10 +55,12 @@ fn run_result(
     smoke_module: &[u8],
     simple_add_module: &[u8],
     simple_host_fn_module: &[u8],
+    simple_floats_module: &[u8],
 ) -> Result<()> {
     smoke(smoke_module)?;
     simple_add(simple_add_module)?;
     simple_host_fn(simple_host_fn_module)?;
+    simple_floats(simple_floats_module)?;
     Ok(())
 }

@@ -78,7 +83,7 @@ fn simple_add(module: &[u8]) -> Result<()> {
     let mut store = Store::new(&engine, ());
     let instance = Linker::new(&engine).instantiate(&mut store, &module)?;
     let func = instance.get_typed_func::<(u32, u32), u32>(&mut store, "add")?;
-    assert_eq!(func.call(&mut store, (2, 3))?, 5);
+    ensure!(func.call(&mut store, (2, 3))? == 5);
     Ok(())
 }

@@ -93,7 +98,20 @@ fn simple_host_fn(module: &[u8]) -> Result<()> {
     let mut store = Store::new(&engine, ());
     let instance = linker.instantiate(&mut store, &module)?;
     let func = instance.get_typed_func::<(u32, u32, u32), u32>(&mut store, "add_and_mul")?;
-    assert_eq!(func.call(&mut store, (2, 3, 4))?, 10);
+    ensure!(func.call(&mut store, (2, 3, 4))? == 10);
+    Ok(())
+}
+
+fn simple_floats(module: &[u8]) -> Result<()> {
+    let engine = Engine::default();
+    let module = match deserialize(&engine, module)? {
+        Some(module) => module,
+        None => panic!(),
+    };
+    let mut store = Store::new(&engine, ());
+    let instance = Linker::new(&engine).instantiate(&mut store, &module)?;
+    let func = instance.get_typed_func::<(f32, f32), f32>(&mut store, "frob")?;
+    ensure!(func.call(&mut store, (1.4, 3.2))? == 5.);
     Ok(())
 }

diff --git a/examples/min-platform/src/main.rs b/examples/min-platform/src/main.rs
index fd1867c6d5..7de14846da 100644
--- a/examples/min-platform/src/main.rs
+++ b/examples/min-platform/src/main.rs
@@ -95,6 +95,16 @@ fn main() -> Result<()> {
             )
         "#,
     )?;
+    let simple_floats = engine.precompile_module(
+        br#"
+            (module
+                (func (export "frob") (param f32 f32) (result f32)
+                    (f32.ceil (local.get 0))
+                    (f32.floor (local.get 0))
+                    f32.add)
+            )
+        "#,
+    )?;

     // Next is an example of running this embedding, which also serves as test
     // that basic functionality actually works.
@@ -134,6 +144,8 @@ fn main() -> Result<()> {
                 usize,
                 *const u8,
                 usize,
+                *const u8,
+                usize,
             ) -> usize,
         > = lib
             .get(b"run")
@@ -149,6 +161,8 @@ fn main() -> Result<()> {
             simple_add.len(),
             simple_host_fn.as_ptr(),
             simple_host_fn.len(),
+            simple_floats.as_ptr(),
+            simple_floats.len(),
         );
         error_buf.set_len(len);

$ MIN_PLATFORM_TEST_DISABLE_WASI=1 WASMTIME_SIGNALS_BASED_TRAPS=1 ./build.sh x86_64-unknown-none
...
Error: Condition failed: `func.call(&mut store, (1.4, 3.2))? == 5.` (2.8 vs 5.0)

Personally I'm tempted to (a) add a "soft float" feature to Cranelift and assert in ABI code that if this feature is enabled that no floats are used, and then (b) update libcalls to unconditionally use GPR arguments/results instead of XMM args/results. (aka do the mov-xmm-to-gpr in Cranelift). Then Wasmtime would configure this soft float flag for the x86_64-unknown-none target and would additionally add runtime checks for SSE/SSE2 which it lacks today.

That should get everything working between compiled wasm code and Wasmtime. Libcalls are slow but they always are. Libcalls are easily avoided as well by enabling more CPU features (e.g. up to SSE4.1 or even up to AVX). Given that I'm not keen on investing a lot of effort into this when performance is basically secondary.

Stream: git-wasmtime

Topic: wasmtime / issue #11506 Compiling wasmtime for the embedd...

Wasmtime GitHub notifications bot (Aug 22 2025 at 00:36):

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