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Add public Compiler::get_published_trampoline #243

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sunfishcode merged 1 commit into from
Aug 7, 2019
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Add public Compiler::get_published_trampoline #243

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12 changes: 12 additions & 0 deletions wasmtime-jit/src/compiler.rs
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Expand Up @@ -151,6 +151,18 @@ impl Compiler {
})
}

/// Create and publish a trampoline for invoking a function.
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@sunfishcode sunfishcode Aug 7, 2019

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Could you add a comment to get_trampoline mentioning that the code it returns needs to be published (with publish_compiled_code) before it can be executed, and pointing to get_published_trampoline as a way to have this done automatically?

And, we should mention that calling get_published_trampoline many times will use memory inefficiently, because publishing between each trampoline creation means we'll use a whole page for each trampoline. When feasible, it's preferable to create all the trampolines (with get_trampoline) first, and then call publish_compiled_code once.

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@sunfishcode sunfishcode Aug 7, 2019

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Actually, looking at this more, get_trampoline and publish_compiled_code are not public functions, so these comments wouldn't immediately make sense. I think this is a symptom of cranelift-jit not being entirely clear about what level of API it wants to be. Hopefully we'll sort all this out with the new APIs.

pub fn get_published_trampoline(
&mut self,
callee_address: *const VMFunctionBody,
signature: &ir::Signature,
value_size: usize,
) -> Result<*const VMFunctionBody, SetupError> {
let result = self.get_trampoline(callee_address, signature, value_size)?;
self.publish_compiled_code();
Ok(result)
}

/// Make memory containing compiled code executable.
pub(crate) fn publish_compiled_code(&mut self) {
self.code_memory.publish();
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