Merge pull request #537 from wasmerio/feature/prehashed-keys

Add hidden flag `--cache-key` to use prehashed modules for speed

CHANGELOG.md

@@ -5,8 +5,10 @@ All PRs to the Wasmer repository must add to this file.
 Blocks of changes will separated by version increments.
 
 ## **[Unreleased]**
+- [#537](https://github.com/wasmerio/wasmer/pull/537) Add hidden flag (`--cache-key`) to use prehashed key into the compiled wasm cache and change compiler backend-specific caching to use directories
+- [#536](https://github.com/wasmerio/wasmer/pull/536) ~Update cache to use compiler backend name in cache key~
+
 ## 0.5.4
-- [#536](https://github.com/wasmerio/wasmer/pull/536) Update cache to use compiler backend name in cache key
 - [#529](https://github.com/wasmerio/wasmer/pull/529) Updates the Wasm Interface library, which is used by wapm, with bug fixes and error message improvements
 
 ## 0.5.3

Cargo.toml

@@ -69,8 +69,8 @@ trace = ["wasmer-runtime-core/trace"]
 extra-debug = ["wasmer-clif-backend/debug", "wasmer-runtime-core/debug"]
 # This feature will allow cargo test to run much faster
 fast-tests = []
-"backend:llvm" = ["wasmer-llvm-backend"]
-"backend:singlepass" = ["wasmer-singlepass-backend"]
+"backend:llvm" = ["wasmer-llvm-backend", "wasmer-runtime-core/backend:llvm"]
+"backend:singlepass" = ["wasmer-singlepass-backend", "wasmer-runtime-core/backend:singlepass"]
 wasi = ["wasmer-wasi"]
 # vfs = ["wasmer-runtime-abi"]
 

lib/runtime-core/Cargo.toml

@@ -54,3 +54,6 @@ cc = "1.0"
 [features]
 debug = []
 trace = ["debug"]
+# backend flags used in conditional compilation of Backend::variants
+"backend:singlepass" = []
+"backend:llvm" = []

lib/runtime-core/src/cache.rs

@@ -37,31 +37,17 @@ impl From<io::Error> for Error {
 pub struct WasmHash([u8; 32], [u8; 32]);
 
 impl WasmHash {
-    /// Hash a wasm module for the default compiler backend.
-    ///
-    /// See also: `WasmHash::generate_for_backend`.
+    /// Hash a wasm module.
     ///
     /// # Note:
     /// This does no verification that the supplied data
     /// is, in fact, a wasm module.
     pub fn generate(wasm: &[u8]) -> Self {
-        WasmHash::generate_for_backend(wasm, Backend::default())
-    }
-
-    /// Hash a wasm module for a specific compiler backend.
-    /// This allows multiple cache entries containing the same compiled
-    /// module with different compiler backends.
-    ///
-    /// # Note:
-    /// This function also does no verification that the supplied data
-    /// is a wasm module
-    pub fn generate_for_backend(wasm: &[u8], backend: Backend) -> Self {
         let mut first_part = [0u8; 32];
         let mut second_part = [0u8; 32];
 
         let mut state = blake2bp::State::new();
         state.update(wasm);
-        state.update(backend.to_string().as_bytes());
 
         let hasher = state.finalize();
         let generic_array = hasher.as_bytes();
@@ -77,6 +63,30 @@ impl WasmHash {
         hex::encode(&self.into_array() as &[u8])
     }
 
+    /// Create hash from hexadecimal representation
+    pub fn decode(hex_str: &str) -> Result<Self, Error> {
+        let bytes = hex::decode(hex_str).map_err(|e| {
+            Error::DeserializeError(format!(
+                "Could not decode prehashed key as hexadecimal: {}",
+                e
+            ))
+        })?;
+        if bytes.len() != 64 {
+            return Err(Error::DeserializeError(
+                "Prehashed keys must deserialze into exactly 64 bytes".to_string(),
+            ));
+        }
+        use std::convert::TryInto;
+        Ok(WasmHash(
+            bytes[0..32].try_into().map_err(|e| {
+                Error::DeserializeError(format!("Could not get first 32 bytes: {}", e))
+            })?,
+            bytes[32..64].try_into().map_err(|e| {
+                Error::DeserializeError(format!("Could not get last 32 bytes: {}", e))
+            })?,
+        ))
+    }
+
     pub(crate) fn into_array(self) -> [u8; 64] {
         let mut total = [0u8; 64];
         total[0..32].copy_from_slice(&self.0);
@@ -219,7 +229,11 @@ pub trait Cache {
     type LoadError: fmt::Debug;
     type StoreError: fmt::Debug;
 
+    /// loads a module using the default `Backend`
     fn load(&self, key: WasmHash) -> Result<Module, Self::LoadError>;
+    /// loads a cached module using a specific `Backend`
+    fn load_with_backend(&self, key: WasmHash, backend: Backend)
+        -> Result<Module, Self::LoadError>;
     fn store(&mut self, key: WasmHash, module: Module) -> Result<(), Self::StoreError>;
 }
 

lib/runtime/src/cache.rs

@@ -7,7 +7,10 @@ use std::{
 };
 
 use wasmer_runtime_core::cache::Error as CacheError;
-pub use wasmer_runtime_core::cache::{Artifact, Cache, WasmHash, WASMER_VERSION_HASH};
+pub use wasmer_runtime_core::{
+    backend::Backend,
+    cache::{Artifact, Cache, WasmHash, WASMER_VERSION_HASH},
+};
 
 /// Representation of a directory that contains compiled wasm artifacts.
 ///
@@ -20,7 +23,6 @@ pub use wasmer_runtime_core::cache::{Artifact, Cache, WasmHash, WASMER_VERSION_H
 ///
 /// ```rust
 /// use wasmer_runtime::cache::{Cache, FileSystemCache, WasmHash};
-/// use wasmer_runtime_core::backend::Backend;
 ///
 /// # use wasmer_runtime::{Module, error::CacheError};
 /// fn store_module(module: Module) -> Result<Module, CacheError> {
@@ -29,7 +31,7 @@ pub use wasmer_runtime_core::cache::{Artifact, Cache, WasmHash, WASMER_VERSION_H
 ///     // corrupted or tampered with.
 ///     let mut fs_cache = unsafe { FileSystemCache::new("some/directory/goes/here")? };
 ///     // Compute a key for a given WebAssembly binary
-///     let key = WasmHash::generate_for_backend(&[], Backend::Cranelift);
+///     let key = WasmHash::generate(&[]);
 ///     // Store a module into the cache given a key
 ///     fs_cache.store(key, module.clone())?;
 ///     Ok(module)
@@ -88,8 +90,13 @@ impl Cache for FileSystemCache {
     type StoreError = CacheError;
 
     fn load(&self, key: WasmHash) -> Result<Module, CacheError> {
+        self.load_with_backend(key, Backend::default())
+    }
+
+    fn load_with_backend(&self, key: WasmHash, backend: Backend) -> Result<Module, CacheError> {
         let filename = key.encode();
         let mut new_path_buf = self.path.clone();
+        new_path_buf.push(backend.to_string());
         new_path_buf.push(filename);
         let file = File::open(new_path_buf)?;
         let mmap = unsafe { Mmap::map(&file)? };
@@ -102,12 +109,15 @@ impl Cache for FileSystemCache {
 
     fn store(&mut self, key: WasmHash, module: Module) -> Result<(), CacheError> {
         let filename = key.encode();
+        let backend_str = module.info().backend.to_string();
         let mut new_path_buf = self.path.clone();
-        new_path_buf.push(filename);
+        new_path_buf.push(backend_str);
 
         let serialized_cache = module.cache()?;
         let buffer = serialized_cache.serialize()?;
 
+        std::fs::create_dir_all(&new_path_buf)?;
+        new_path_buf.push(filename);
         let mut file = File::create(new_path_buf)?;
         file.write_all(&buffer)?;
 

src/bin/wasmer.rs

@@ -24,6 +24,7 @@ use wasmer_runtime::{
 use wasmer_runtime_core::{
     self,
     backend::{Backend, Compiler, CompilerConfig, MemoryBoundCheckMode},
+    debug,
     loader::{Instance as LoadedInstance, LocalLoader},
 };
 #[cfg(feature = "backend:singlepass")]
@@ -115,9 +116,18 @@ struct Run {
     #[structopt(long = "resume")]
     resume: Option<String>,
 
+    /// The command name is a string that will override the first argument passed
+    /// to the wasm program. This is used in wapm to provide nicer output in
+    /// help commands and error messages of the running wasm program
     #[structopt(long = "command-name", hidden = true)]
     command_name: Option<String>,
 
+    /// A prehashed string, used to speed up start times by avoiding hashing the
+    /// wasm module. If the specified hash is not found, Wasmer will hash the module
+    /// as if no `cache-key` argument was passed.
+    #[structopt(long = "cache-key", hidden = true)]
+    cache_key: Option<String>,
+
     /// Application arguments
     #[structopt(name = "--", raw(multiple = "true"))]
     args: Vec<String>,
@@ -350,10 +360,6 @@ fn execute_wasm(options: &Run) -> Result<(), String> {
     } else {
         // If we have cache enabled
 
-        // We generate a hash for the given binary, so we can use it as key
-        // for the Filesystem cache
-        let hash = WasmHash::generate_for_backend(&wasm_binary, options.backend);
-
         let wasmer_cache_dir = get_cache_dir();
 
         // We create a new cache instance.
@@ -362,14 +368,29 @@ fn execute_wasm(options: &Run) -> Result<(), String> {
         let mut cache = unsafe {
             FileSystemCache::new(wasmer_cache_dir).map_err(|e| format!("Cache error: {:?}", e))?
         };
+        let load_cache_key = || -> Result<_, String> {
+            if let Some(ref prehashed_cache_key) = options.cache_key {
+                if let Ok(module) =
+                    WasmHash::decode(prehashed_cache_key).and_then(|prehashed_key| {
+                        cache.load_with_backend(prehashed_key, options.backend)
+                    })
+                {
+                    debug!("using prehashed key: {}", prehashed_cache_key);
+                    return Ok(module);
+                }
+            }
+
+            // We generate a hash for the given binary, so we can use it as key
+            // for the Filesystem cache
+            let hash = WasmHash::generate(&wasm_binary);
 
             // cache.load will return the Module if it's able to deserialize it properly, and an error if:
             // * The file is not found
             // * The file exists, but it's corrupted or can't be converted to a module
-        match cache.load(hash) {
+            match cache.load_with_backend(hash, options.backend) {
                 Ok(module) => {
                     // We are able to load the module from cache
-                module
+                    Ok(module)
                 }
                 Err(_) => {
                     let module = webassembly::compile_with_config_with(
@@ -384,11 +405,14 @@ fn execute_wasm(options: &Run) -> Result<(), String> {
                     // We try to save the module into a cache file
                     cache.store(hash, module.clone()).unwrap_or_default();
 
-                module
+                    Ok(module)
                 }
             }
         };
 
+        load_cache_key()?
+    };
+
     if let Some(loader) = options.loader {
         let mut import_object = wasmer_runtime_core::import::ImportObject::new();
         import_object.allow_missing_functions = true; // Import initialization might be left to the loader.