fix: Fix segmentation fault in tests on CPUs with PKU support (#471)

Due to V8's PKU feature, only the thread that initialized the V8
platform or those spawned from it can access the isolates; other threads
will get a segmentation fault. Since each test runs in its thread, they
crash on newer CPUs that support PKU.

This issue has two possible solutions:
1. Initialize the platform once in the main thread.
2. Turn off the PKU feature during testing.

This issue was already encountered for the `deno test` command, which
was resolved by initializing the platform in the main thread
(denoland/deno#20495).

In the case of rust tests, the same solution cannot be used, as the
default test runner does not allow running code on the main thread
before any test runs.

My proposed solution is to add a feature flag to deno_core, which, when
enabled, uses the unprotected platform. An alternative solution could be
to call `deno_core::JsRuntime::init_platform` at the beginning of each
test.

This PR will also be a step towards fixing denoland/deno#21439

core/Cargo.toml

@@ -19,6 +19,7 @@ include_icu_data = []
 v8_use_custom_libcxx = ["v8/use_custom_libcxx"]
 include_js_files_for_snapshotting = []
 unsafe_runtime_options = []
+unsafe_use_unprotected_platform = []
 
 # Use the old, slower (but better tested) JoinSet driver
 op_driver_joinset = []

core/runtime/jsruntime.rs

@@ -413,8 +413,15 @@ fn v8_init(
   };
   v8::V8::set_flags_from_string(&flags);
 
-  let v8_platform = v8_platform
-    .unwrap_or_else(|| v8::new_default_platform(0, false).make_shared());
+  let v8_platform = v8_platform.unwrap_or_else(|| {
+    if cfg!(any(test, feature = "unsafe_use_unprotected_platform")) {
+      // We want to use the unprotected platform for unit tests
+      v8::new_unprotected_default_platform(0, false)
+    } else {
+      v8::new_default_platform(0, false)
+    }
+    .make_shared()
+  });
   v8::V8::initialize_platform(v8_platform.clone());
   v8::V8::initialize();
 

serde_v8/Cargo.toml

@@ -23,6 +23,7 @@ thiserror.workspace = true
 v8.workspace = true
 
 [dev-dependencies]
+serde_v8_utilities = { path = "./utilities" }
 bencher.workspace = true
 serde_json.workspace = true
 serde_bytes.workspace = true

serde_v8/benches/de.rs

@@ -5,9 +5,9 @@ use bencher::Bencher;
 
 use serde::Deserialize;
 
-use serde_v8::utils::js_exec;
-use serde_v8::utils::v8_do;
 use serde_v8::ByteString;
+use serde_v8_utilities::js_exec;
+use serde_v8_utilities::v8_do;
 
 #[derive(Debug, Deserialize, PartialEq)]
 struct MathOp {

serde_v8/benches/ser.rs

@@ -5,8 +5,8 @@ use bencher::Bencher;
 
 use serde::Serialize;
 
-use serde_v8::utils::v8_do;
 use serde_v8::ByteString;
+use serde_v8_utilities::v8_do;
 
 #[derive(Serialize)]
 struct MathOp {

serde_v8/lib.rs

@@ -6,7 +6,6 @@ mod magic;
 mod payload;
 mod ser;
 mod serializable;
-pub mod utils;
 
 pub use de::from_v8;
 pub use de::from_v8_cached;

serde_v8/magic/v8slice.rs

@@ -107,7 +107,8 @@ where
     static V8_ONCE: std::sync::Once = std::sync::Once::new();
 
     V8_ONCE.call_once(|| {
-      let platform = v8::new_default_platform(0, false).make_shared();
+      let platform =
+        v8::new_unprotected_default_platform(0, false).make_shared();
       v8::V8::initialize_platform(platform);
       v8::V8::initialize();
     });

serde_v8/tests/de.rs

@@ -2,13 +2,13 @@
 use serde::Deserialize;
 use serde::Deserializer;
 
-use serde_v8::utils::js_exec;
-use serde_v8::utils::v8_do;
 use serde_v8::BigInt;
 use serde_v8::ByteString;
 use serde_v8::Error;
 use serde_v8::JsBuffer;
 use serde_v8::U16String;
+use serde_v8_utilities::js_exec;
+use serde_v8_utilities::v8_do;
 
 #[derive(Debug, Deserialize, PartialEq)]
 struct MathOp {

serde_v8/tests/magic.rs

@@ -2,9 +2,9 @@
 use serde::Deserialize;
 use serde::Serialize;
 
-use serde_v8::utils::js_exec;
-use serde_v8::utils::v8_do;
 use serde_v8::Result;
+use serde_v8_utilities::js_exec;
+use serde_v8_utilities::v8_do;
 
 #[derive(Deserialize)]
 struct MagicOp<'s> {

serde_v8/tests/ser.rs

@@ -1,9 +1,9 @@
 // Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
 use serde::Serialize;
 use serde_json::json;
-use serde_v8::utils::js_exec;
-use serde_v8::utils::v8_do;
 use serde_v8::BigInt;
+use serde_v8_utilities::js_exec;
+use serde_v8_utilities::v8_do;
 
 #[derive(Debug, Serialize, PartialEq)]
 struct MathOp {

serde_v8/utilities/Cargo.toml

@@ -0,0 +1,11 @@
+# Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+
+[package]
+name = "serde_v8_utilities"
+version = "0.0.0"
+
+[lib]
+path = "lib.rs"
+
+[dependencies]
+v8.workspace = true

serde_v8/utils.rs → serde_v8/utilities/lib.rs

@@ -11,7 +11,7 @@ pub fn js_exec<'s>(
 }
 
 pub fn v8_init() {
-  let platform = v8::new_default_platform(0, false).make_shared();
+  let platform = v8::new_unprotected_default_platform(0, false).make_shared();
   v8::V8::initialize_platform(platform);
   v8::V8::initialize();
 }

testing/Cargo.toml

@@ -15,6 +15,7 @@ path = "./lib.rs"
 
 [dev-dependencies]
 deno_core.workspace = true
+deno_core.features = ["unsafe_use_unprotected_platform"]
 pretty_assertions.workspace = true
 prettyplease.workspace = true
 testing_macros.workspace = true