Fix wasmtime settings command. (#8060) (#8127)

* Fix `wasmtime settings` command.

Currently the `settings` command panics because the tunables are not set in the
compiler builder.

This commit creates a default tunables based on either the target triple passed
on the command line or uses the default for the host.

Fixes #8058.

* Additional clean up.

Co-authored-by: Peter Huene <[email protected]>

crates/environ/src/tunables.rs

@@ -1,4 +1,6 @@
+use anyhow::{anyhow, bail, Result};
 use serde_derive::{Deserialize, Serialize};
+use target_lexicon::{PointerWidth, Triple};
 
 /// Tunable parameters for WebAssembly compilation.
 #[derive(Clone, Hash, Serialize, Deserialize, Debug)]
@@ -70,6 +72,18 @@ impl Tunables {
         }
     }
 
+    /// Returns the default set of tunables for the given target triple.
+    pub fn default_for_target(target: &Triple) -> Result<Self> {
+        match target
+            .pointer_width()
+            .map_err(|_| anyhow!("failed to retrieve target pointer width"))?
+        {
+            PointerWidth::U32 => Ok(Tunables::default_u32()),
+            PointerWidth::U64 => Ok(Tunables::default_u64()),
+            _ => bail!("unsupported target pointer width"),
+        }
+    }
+
     /// Returns the default set of tunables for running under MIRI.
     pub fn default_miri() -> Tunables {
         Tunables {

crates/wasmtime/src/config.rs

@@ -6,7 +6,7 @@ use std::fmt;
 use std::path::Path;
 use std::str::FromStr;
 use std::sync::Arc;
-use target_lexicon::{Architecture, PointerWidth};
+use target_lexicon::Architecture;
 use wasmparser::WasmFeatures;
 #[cfg(feature = "cache")]
 use wasmtime_cache::CacheConfig;
@@ -1684,11 +1684,7 @@ impl Config {
         let mut tunables = Tunables::default_host();
         #[cfg(any(feature = "cranelift", feature = "winch"))]
         let mut tunables = match &self.compiler_config.target.as_ref() {
-            Some(target) => match target.pointer_width() {
-                Ok(PointerWidth::U32) => Tunables::default_u32(),
-                Ok(PointerWidth::U64) => Tunables::default_u64(),
-                _ => bail!("unknown pointer width"),
-            },
+            Some(target) => Tunables::default_for_target(target)?,
             None => Tunables::default_host(),
         };
 

src/commands/settings.rs

@@ -5,7 +5,7 @@ use clap::Parser;
 use serde::{ser::SerializeMap, Serialize};
 use std::collections::BTreeMap;
 use std::str::FromStr;
-use wasmtime_environ::{CompilerBuilder, FlagValue, Setting, SettingKind};
+use wasmtime_environ::{CompilerBuilder, FlagValue, Setting, SettingKind, Tunables};
 
 /// Displays available Cranelift settings for a target.
 #[derive(Parser, PartialEq)]
@@ -108,10 +108,16 @@ impl SettingsCommand {
     pub fn execute(self) -> Result<()> {
         // Gather settings from the cranelift compiler builder
         let mut builder = wasmtime_cranelift::builder(None)?;
-        if let Some(target) = &self.target {
+        let tunables = if let Some(target) = &self.target {
             let target = target_lexicon::Triple::from_str(target).map_err(|e| anyhow!(e))?;
+            let tunables = Tunables::default_for_target(&target)?;
             builder.target(target)?;
-        }
+            tunables
+        } else {
+            Tunables::default_host()
+        };
+
+        builder.set_tunables(tunables)?;
         let mut settings = Settings::from_builder(&builder);
 
         // Add inferred settings if no target specified

tests/all/cli_tests.rs

@@ -1588,3 +1588,10 @@ mod test_programs {
         Ok(())
     }
 }
+
+#[test]
+fn settings_command() -> Result<()> {
+    let output = run_wasmtime(&["settings"])?;
+    assert!(output.contains("Cranelift settings for target"));
+    Ok(())
+}