From fb7f1bd0eddea4a5fcf78b8420b58174b2299194 Mon Sep 17 00:00:00 2001
From: Albert Marashi <albert@lumina.earth>
Date: Fri, 13 Feb 2026 16:46:34 +1030
Subject: [PATCH 1/3] Expose an unsafe value pointer API to the global

Implement the ability to obtain an unsafe raw pointer into global variable memory in webasembly modules.
---
 .../wasmtime/src/runtime/externals/global.rs  | 41 +++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/crates/wasmtime/src/runtime/externals/global.rs b/crates/wasmtime/src/runtime/externals/global.rs
index 8927793fca33..abebc22cdaed 100644
--- a/crates/wasmtime/src/runtime/externals/global.rs
+++ b/crates/wasmtime/src/runtime/externals/global.rs
@@ -208,6 +208,47 @@ impl Global {
         }
     }
 
+    /// Returns a raw pointer to this global's underlying storage.
+    ///
+    /// This is useful for cross-thread signaling scenarios (e.g. cooperative
+    /// scheduling) where one thread needs to write a flag that a running
+    /// WebAssembly module checks periodically without requiring `&mut Store`.
+    ///
+    /// The returned pointer points to a 16-byte aligned `VMGlobalDefinition`
+    /// whose first bytes store the value in native endian format. For an `i32`
+    /// global, the value occupies the first 4 bytes.
+    ///
+    /// # Safety
+    ///
+    /// - The pointer is valid for the lifetime of the `Store` that owns this
+    ///   global. Using it after the store is dropped is undefined behavior.
+    /// - For numeric types (i32, i64, f32, f64), writing to this pointer from
+    ///   another thread is safe on architectures where aligned 4/8-byte writes
+    ///   are atomic (x86, ARM64), but Rust's memory model technically considers
+    ///   this a data race. Callers should use `AtomicI32::from_ptr` or
+    ///   `write_volatile` to avoid UB.
+    /// - This must NOT be used for reference types (funcref, externref, etc.)
+    ///   as those require GC coordination.
+    /// - The global must be mutable (`Mutability::Var`).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `store` does not own this global.
+    pub unsafe fn value_ptr(&self, store: impl AsContext) -> *mut u8 {
+        let store = store.as_context().0;
+        assert!(
+            self._ty(store).mutability() == Mutability::Var,
+            "value_ptr requires a mutable global"
+        );
+        let content = self._ty(store).content();
+        assert!(
+            matches!(content, ValType::I32 | ValType::I64 | ValType::F32 | ValType::F64),
+            "value_ptr only supports numeric types, got {:?}",
+            content,
+        );
+        self.definition(store).as_ptr().cast()
+    }
+
     /// Attempts to set the current value of this global to [`Val`].
     ///
     /// # Errors

From c7c77a00acd6fdd9a46ca8eda03eb4b2f000aee8 Mon Sep 17 00:00:00 2001
From: Albert Marashi <albert@lumina.earth>
Date: Fri, 13 Feb 2026 16:58:04 +1030
Subject: [PATCH 2/3] Fix free after use

---
 crates/wasmtime/src/runtime/externals/global.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/crates/wasmtime/src/runtime/externals/global.rs b/crates/wasmtime/src/runtime/externals/global.rs
index abebc22cdaed..6285517e3ada 100644
--- a/crates/wasmtime/src/runtime/externals/global.rs
+++ b/crates/wasmtime/src/runtime/externals/global.rs
@@ -240,7 +240,8 @@ impl Global {
             self._ty(store).mutability() == Mutability::Var,
             "value_ptr requires a mutable global"
         );
-        let content = self._ty(store).content();
+        let binding = self._ty(store);
+        let content = binding.content();
         assert!(
             matches!(content, ValType::I32 | ValType::I64 | ValType::F32 | ValType::F64),
             "value_ptr only supports numeric types, got {:?}",

From 1adc57ea2768f78074879082fdd1ffe4fd50df62 Mon Sep 17 00:00:00 2001
From: Albert Marashi <albert@lumina.earth>
Date: Fri, 13 Feb 2026 17:03:30 +1030
Subject: [PATCH 3/3] fix formatting issue

---
 crates/wasmtime/src/runtime/externals/global.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/crates/wasmtime/src/runtime/externals/global.rs b/crates/wasmtime/src/runtime/externals/global.rs
index 6285517e3ada..7c19b3e5e072 100644
--- a/crates/wasmtime/src/runtime/externals/global.rs
+++ b/crates/wasmtime/src/runtime/externals/global.rs
@@ -243,7 +243,10 @@ impl Global {
         let binding = self._ty(store);
         let content = binding.content();
         assert!(
-            matches!(content, ValType::I32 | ValType::I64 | ValType::F32 | ValType::F64),
+            matches!(
+                content,
+                ValType::I32 | ValType::I64 | ValType::F32 | ValType::F64
+            ),
             "value_ptr only supports numeric types, got {:?}",
             content,
         );