tiering.rs

//! The tiering module supports switching between code compiled with different optimization levels
//! as runtime.
use crate::backend::{Compiler, CompilerConfig};
use crate::compile_with_config;
use crate::fault::{
    catch_unsafe_unwind, ensure_sighandler, pop_code_version, push_code_version, with_ctx,
};
use crate::fault::{set_wasm_interrupt_on_ctx, was_sigint_triggered_fault};
use crate::import::ImportObject;
use crate::instance::Instance;
use crate::module::{Module, ModuleInfo};
use crate::state::{x64::invoke_call_return_on_stack, CodeVersion, InstanceImage};
use crate::vm::Ctx;

use std::cell::Cell;
use std::sync::{Arc, Mutex};

struct Defer<F: FnOnce()>(Option<F>);
impl<F: FnOnce()> Drop for Defer<F> {
    fn drop(&mut self) {
        if let Some(f) = self.0.take() {
            f();
        }
    }
}

/// Kind of shell exit operation.
pub enum ShellExitOperation {
    /// Operation to continue with an instance image.
    ContinueWith(InstanceImage),
}

/// Context for an interactive shell.
pub struct InteractiveShellContext {
    /// Optional instance image.
    pub image: Option<InstanceImage>,
    /// Flag to indicate patching.
    pub patched: bool,
}

struct OptimizationState {
    outcome: Mutex<Option<OptimizationOutcome>>,
}

struct OptimizationOutcome {
    backend_id: &'static str,
    module: Module,
}

#[repr(transparent)]
struct CtxWrapper(*mut Ctx);
unsafe impl Send for CtxWrapper {}
unsafe impl Sync for CtxWrapper {}

unsafe fn do_optimize(
    binary: &[u8],
    backend_id: &'static str,
    compiler: Box<dyn Compiler>,
    ctx: &Mutex<CtxWrapper>,
    state: &OptimizationState,
) {
    let module = match compile_with_config(
        &binary[..],
        &*compiler,
        CompilerConfig {
            symbol_map: None,
            track_state: true,
            ..Default::default()
        },
    ) {
        Ok(x) => x,
        Err(_) => return,
    };

    let ctx_inner = ctx.lock().unwrap();
    if !ctx_inner.0.is_null() {
        *state.outcome.lock().unwrap() = Some(OptimizationOutcome { backend_id, module });
        set_wasm_interrupt_on_ctx(ctx_inner.0);
    }
}

/// Runs an instance with tiering.
pub unsafe fn run_tiering<F: Fn(InteractiveShellContext) -> ShellExitOperation>(
    module_info: &ModuleInfo,
    wasm_binary: &[u8],
    mut resume_image: Option<InstanceImage>,
    import_object: &ImportObject,
    start_raw: extern "C" fn(&mut Ctx),
    baseline: &mut Instance,
    baseline_backend: &'static str,
    optimized_backends: Vec<(&'static str, Box<dyn Fn() -> Box<dyn Compiler> + Send>)>,
    interactive_shell: F,
) -> Result<(), String> {
    ensure_sighandler();

    let ctx_box = Arc::new(Mutex::new(CtxWrapper(baseline.context_mut() as *mut _)));
    // Ensure that the ctx pointer's lifetime is not longer than Instance's.
    let _deferred_ctx_box_cleanup: Defer<_> = {
        let ctx_box = ctx_box.clone();
        Defer(Some(move || {
            ctx_box.lock().unwrap().0 = ::std::ptr::null_mut();
        }))
    };
    let opt_state = Arc::new(OptimizationState {
        outcome: Mutex::new(None),
    });

    {
        let wasm_binary = wasm_binary.to_vec();
        let ctx_box = ctx_box.clone();
        let opt_state = opt_state.clone();
        ::std::thread::spawn(move || {
            for (backend_id, backend) in optimized_backends {
                if !ctx_box.lock().unwrap().0.is_null() {
                    do_optimize(&wasm_binary, backend_id, backend(), &ctx_box, &opt_state);
                }
            }
        });
    }

    let mut optimized_instances: Vec<Instance> = vec![];

    push_code_version(CodeVersion {
        baseline: true,
        msm: baseline
            .module
            .runnable_module
            .get_module_state_map()
            .unwrap(),
        base: baseline.module.runnable_module.get_code().unwrap().as_ptr() as usize,
        backend: baseline_backend,
        runnable_module: baseline.module.runnable_module.clone(),
    });
    let n_versions: Cell<usize> = Cell::new(1);

    let _deferred_pop_versions = Defer(Some(|| {
        for _ in 0..n_versions.get() {
            pop_code_version().unwrap();
        }
    }));

    loop {
        let new_optimized: Option<(&'static str, &mut Instance)> = {
            let mut outcome = opt_state.outcome.lock().unwrap();
            if let Some(x) = outcome.take() {
                let instance = x
                    .module
                    .instantiate(&import_object)
                    .map_err(|e| format!("Can't instantiate module: {:?}", e))?;
                // Keep the optimized code alive.
                optimized_instances.push(instance);
                optimized_instances.last_mut().map(|y| (x.backend_id, y))
            } else {
                None
            }
        };
        if let Some((backend_id, optimized)) = new_optimized {
            let base = module_info.imported_functions.len();
            let code_ptr = optimized
                .module
                .runnable_module
                .get_code()
                .unwrap()
                .as_ptr() as usize;
            let target_addresses: Vec<usize> = optimized
                .module
                .runnable_module
                .get_local_function_offsets()
                .unwrap()
                .into_iter()
                .map(|x| code_ptr + x)
                .collect();
            assert_eq!(target_addresses.len(), module_info.func_assoc.len() - base);
            for i in base..module_info.func_assoc.len() {
                baseline
                    .module
                    .runnable_module
                    .patch_local_function(i - base, target_addresses[i - base]);
            }

            push_code_version(CodeVersion {
                baseline: false,
                msm: optimized
                    .module
                    .runnable_module
                    .get_module_state_map()
                    .unwrap(),
                base: optimized
                    .module
                    .runnable_module
                    .get_code()
                    .unwrap()
                    .as_ptr() as usize,
                backend: backend_id,
                runnable_module: optimized.module.runnable_module.clone(),
            });
            n_versions.set(n_versions.get() + 1);

            baseline.context_mut().local_functions = optimized.context_mut().local_functions;
        }
        // Assuming we do not want to do breakpoint-based debugging on optimized backends.
        let breakpoints = baseline.module.runnable_module.get_breakpoints();
        let ctx = baseline.context_mut() as *mut _;
        let ret = with_ctx(ctx, || {
            if let Some(image) = resume_image.take() {
                let msm = baseline
                    .module
                    .runnable_module
                    .get_module_state_map()
                    .unwrap();
                let code_base =
                    baseline.module.runnable_module.get_code().unwrap().as_ptr() as usize;
                invoke_call_return_on_stack(
                    &msm,
                    code_base,
                    image,
                    baseline.context_mut(),
                    breakpoints.clone(),
                )
                .map(|_| ())
            } else {
                catch_unsafe_unwind(|| start_raw(baseline.context_mut()), breakpoints.clone())
            }
        });
        if let Err(e) = ret {
            if let Ok(new_image) = e.downcast::<InstanceImage>() {
                // Tier switch event
                if !was_sigint_triggered_fault() && opt_state.outcome.lock().unwrap().is_some() {
                    resume_image = Some(*new_image);
                    continue;
                }
                let op = interactive_shell(InteractiveShellContext {
                    image: Some(*new_image),
                    patched: n_versions.get() > 1,
                });
                match op {
                    ShellExitOperation::ContinueWith(new_image) => {
                        resume_image = Some(new_image);
                    }
                }
            } else {
                return Err("Error while executing WebAssembly".into());
            }
        } else {
            return Ok(());
        }
    }
}