implement fuzzing for component types (#4537)

This addresses #4307.

For the static API we generate 100 arbitrary test cases at build time, each of
which includes 0-5 parameter types, a result type, and a WAT fragment containing
an imported function and an exported function.  The exported function calls the
imported function, which is implemented by the host.  At runtime, the fuzz test
selects a test case at random and feeds it zero or more sets of arbitrary
parameters and results, checking that values which flow host-to-guest and
guest-to-host make the transition unchanged.

The fuzz test for the dynamic API follows a similar pattern, the only difference
being that test cases are generated at runtime.

Signed-off-by: Joel Dice <[email protected]>

Cargo.toml

@@ -61,6 +61,8 @@ once_cell = "1.9.0"
 rayon = "1.5.0"
 component-macro-test = { path = "crates/misc/component-macro-test" }
 wasmtime-wast = { path = "crates/wast", version = "=0.40.0", features = ['component-model'] }
+component-test-util = { path = "crates/misc/component-test-util" }
+wasmtime-component-util = { path = "crates/component-util" }
 
 [target.'cfg(windows)'.dev-dependencies]
 windows-sys = { version = "0.36.0", features = ["Win32_System_Memory"] }
@@ -110,7 +112,11 @@ memory-init-cow = ["wasmtime/memory-init-cow", "wasmtime-cli-flags/memory-init-c
 pooling-allocator = ["wasmtime/pooling-allocator", "wasmtime-cli-flags/pooling-allocator"]
 all-arch = ["wasmtime/all-arch"]
 posix-signals-on-macos = ["wasmtime/posix-signals-on-macos"]
-component-model = ["wasmtime/component-model", "wasmtime-wast/component-model", "wasmtime-cli-flags/component-model"]
+component-model = [
+  "wasmtime/component-model",
+  "wasmtime-wast/component-model",
+  "wasmtime-cli-flags/component-model"
+]
 
 # Stub feature that does nothing, for Cargo-features compatibility: the new
 # backend is the default now.

build.rs

@@ -41,7 +41,7 @@ fn main() -> anyhow::Result<()> {
             } else {
                 println!(
                     "cargo:warning=The spec testsuite is disabled. To enable, run `git submodule \
-                 update --remote`."
+                     update --remote`."
                 );
             }
             Ok(())

crates/component-macro/src/lib.rs

@@ -885,7 +885,10 @@ impl Expander for ComponentTypeExpander {
                 const SIZE32: usize = {
                     let mut size = 0;
                     #sizes
-                    #internal::align_to(#discriminant_size as usize, Self::ALIGN32) + size
+                    #internal::align_to(
+                        #internal::align_to(#discriminant_size as usize, Self::ALIGN32) + size,
+                        Self::ALIGN32
+                    )
                 };
 
                 const ALIGN32: u32 = {

crates/component-util/src/lib.rs

@@ -77,3 +77,62 @@ impl FlagsSize {
 fn ceiling_divide(n: usize, d: usize) -> usize {
     (n + d - 1) / d
 }
+
+/// A simple bump allocator which can be used with modules
+pub const REALLOC_AND_FREE: &str = r#"
+    (global $last (mut i32) (i32.const 8))
+    (func $realloc (export "realloc")
+        (param $old_ptr i32)
+        (param $old_size i32)
+        (param $align i32)
+        (param $new_size i32)
+        (result i32)
+
+        ;; Test if the old pointer is non-null
+        local.get $old_ptr
+        if
+            ;; If the old size is bigger than the new size then
+            ;; this is a shrink and transparently allow it
+            local.get $old_size
+            local.get $new_size
+            i32.gt_u
+            if
+                local.get $old_ptr
+                return
+            end
+
+            ;; ... otherwise this is unimplemented
+            unreachable
+        end
+
+        ;; align up `$last`
+        (global.set $last
+            (i32.and
+                (i32.add
+                    (global.get $last)
+                    (i32.add
+                        (local.get $align)
+                        (i32.const -1)))
+                (i32.xor
+                    (i32.add
+                        (local.get $align)
+                        (i32.const -1))
+                    (i32.const -1))))
+
+        ;; save the current value of `$last` as the return value
+        global.get $last
+
+        ;; ensure anything necessary is set to valid data by spraying a bit
+        ;; pattern that is invalid
+        global.get $last
+        i32.const 0xde
+        local.get $new_size
+        memory.fill
+
+        ;; bump our pointer
+        (global.set $last
+            (i32.add
+                (global.get $last)
+                (local.get $new_size)))
+    )
+"#;

crates/environ/fuzz/Cargo.toml

@@ -15,6 +15,7 @@ libfuzzer-sys = "0.4"
 wasmparser = "0.88.0"
 wasmprinter = "0.2.37"
 wasmtime-environ = { path = ".." }
+component-fuzz-util = { path = "../../misc/component-fuzz-util", optional = true }
 
 [[bin]]
 name = "fact-valid-module"
@@ -24,4 +25,4 @@ doc = false
 required-features = ["component-model"]
 
 [features]
-component-model = ["wasmtime-environ/component-model"]
+component-model = ["wasmtime-environ/component-model", "dep:component-fuzz-util"]