From b4ebcf0cc61c1c5b82ee5adbf542515d092c7686 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Wed, 6 May 2026 11:19:28 +0200
Subject: [PATCH 01/14] gen-rules: pass source dir explicitly instead of
 probing getcwd

Dune 3.23 forces sandboxing on user rules, so gen.exe runs from
_build/.sandbox/<hash>/default/<dir> instead of the project tree.
The previous prefix walker (stop when parent ends with _build) then
yielded <hash>/default/<dir>/, which both shows up in the generated
;; comment and shifts the Hashtbl.hash-based name suffix, making the
runtest diff against the checked-in dune.inc fail.

Take the project-relative directory as argv.(1) (replacing the
previously unused library-name argument) so the prefix is stable
regardless of where dune runs the action.
---
 .../tests-compiler/double-translation/dune    |  2 +-
 compiler/tests-compiler/dune                  |  2 +-
 compiler/tests-compiler/gen-rules/gen.ml      | 20 +++++++------------
 lib/tests/dune                                |  2 +-
 lib/tests/gen-rules/gen.ml                    | 20 +++++++------------
 5 files changed, 17 insertions(+), 29 deletions(-)

diff --git a/compiler/tests-compiler/double-translation/dune b/compiler/tests-compiler/double-translation/dune
index 063207b8a9..7a16010230 100644
--- a/compiler/tests-compiler/double-translation/dune
+++ b/compiler/tests-compiler/double-translation/dune
@@ -6,7 +6,7 @@
  (action
   (with-stdout-to
    dune.inc.gen
-   (run ../gen-rules/gen.exe jsoo_compiler_test))))
+   (run ../gen-rules/gen.exe compiler/tests-compiler/double-translation))))
 
 (rule
  (alias runtest)
diff --git a/compiler/tests-compiler/dune b/compiler/tests-compiler/dune
index bf40299a44..6702f7246f 100644
--- a/compiler/tests-compiler/dune
+++ b/compiler/tests-compiler/dune
@@ -6,7 +6,7 @@
  (action
   (with-stdout-to
    dune.inc.gen
-   (run gen-rules/gen.exe jsoo_compiler_test))))
+   (run gen-rules/gen.exe compiler/tests-compiler))))
 
 (rule
  (alias runtest)
diff --git a/compiler/tests-compiler/gen-rules/gen.ml b/compiler/tests-compiler/gen-rules/gen.ml
index b2b83f4de7..14b81d6d6c 100644
--- a/compiler/tests-compiler/gen-rules/gen.ml
+++ b/compiler/tests-compiler/gen-rules/gen.ml
@@ -14,20 +14,14 @@ let is_implem x =
 
 let () = set_binary_mode_out stdout true
 
+(* Project-relative path to this directory, passed by dune *)
 let prefix : string =
-  let rec loop acc rem =
-    let basename = Filename.basename rem in
-    let dirname = Filename.dirname rem in
-    if
-      String.equal dirname rem
-      || String.ends_with ~suffix:"_build" dirname
-      || Sys.file_exists (Filename.concat rem "dune-project")
-    then acc
-    else
-      let acc = basename :: acc in
-      loop acc dirname
-  in
-  loop [ "" ] (Sys.getcwd ()) |> String.concat ~sep:"/"
+  if Array.length Sys.argv < 2
+  then failwith "gen.exe: expected source directory as first argument";
+  let p = Sys.argv.(1) in
+  if String.length p > 0 && not (Char.equal p.[String.length p - 1] '/')
+  then p ^ "/"
+  else p
 
 type lang =
   | Not of lang
diff --git a/lib/tests/dune b/lib/tests/dune
index f4902cdc3a..30c19e35c1 100644
--- a/lib/tests/dune
+++ b/lib/tests/dune
@@ -6,7 +6,7 @@
  (action
   (with-stdout-to
    dune.inc.gen
-   (run gen-rules/gen.exe jsoo_lib_expect_tests))))
+   (run gen-rules/gen.exe lib/tests))))
 
 (rule
  (alias runtest)
diff --git a/lib/tests/gen-rules/gen.ml b/lib/tests/gen-rules/gen.ml
index 2899edb21e..f02a880746 100644
--- a/lib/tests/gen-rules/gen.ml
+++ b/lib/tests/gen-rules/gen.ml
@@ -32,20 +32,14 @@ let is_implem x =
 
 let () = set_binary_mode_out stdout true
 
+(* Project-relative path to this directory, passed by dune *)
 let prefix : string =
-  let rec loop acc rem =
-    let basename = Filename.basename rem in
-    let dirname = Filename.dirname rem in
-    if
-      String.equal dirname rem
-      || String.ends_with ~suffix:"_build" dirname
-      || Sys.file_exists (Filename.concat rem "dune-project")
-    then acc
-    else
-      let acc = basename :: acc in
-      loop acc dirname
-  in
-  loop [ "" ] (Sys.getcwd ()) |> String.concat ~sep:"/"
+  if Array.length Sys.argv < 2
+  then failwith "gen.exe: expected source directory as first argument";
+  let p = Sys.argv.(1) in
+  if String.length p > 0 && not (Char.equal p.[String.length p - 1] '/')
+  then p ^ "/"
+  else p
 
 type enabled_if =
   | GE5

From f26d6d71d7d905d0b13ad0c9e260f6f2d43a3ac3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Wed, 6 May 2026 11:19:28 +0200
Subject: [PATCH 02/14] Pin ocaml-dune-lint dev

The current release of ocaml-dune-lint is not compatible with dune 3.23.
---
 .github/workflows/lint.yml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 00cdd669fe..714b254e23 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -26,6 +26,7 @@ jobs:
         with:
           token: ${{ github.token }}
       - run: sh tools/make_opam_dune_lint_dir.sh
+      - run: opam pin -n opam-dune-lint --dev-repo
       - uses: ocaml/setup-ocaml/lint-opam@v3
 
   lint-fmt:

From 69acef3637f8296722f9414e04369f36f2c7d736 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Wed, 6 May 2026 13:58:07 +0200
Subject: [PATCH 03/14] Tests: declare dependency on wasm assets directory

Under dune 3.23 sandboxing, rules that run a *.bc.wasm.js file also
need to depend on the companion *.bc.wasm.assets/ directory so that
the .wasm files are copied into the sandbox.
---
 compiler/tests-dynlink-wasm/dune             | 20 ++++++++++++++++----
 compiler/tests-ocaml/lib-arg/dune            |  2 ++
 compiler/tests-ocaml/lib-array/dune          |  2 ++
 compiler/tests-ocaml/lib-either/dune         |  2 ++
 compiler/tests-ocaml/lib-internalformat/dune |  2 ++
 compiler/tests-ocaml/lib-lazy/dune           |  2 ++
 compiler/tests-predef/dune                   |  2 ++
 compiler/tests-toplevel/dune                 |  2 ++
 8 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/compiler/tests-dynlink-wasm/dune b/compiler/tests-dynlink-wasm/dune
index dc5fea7c01..cabbf6ecff 100644
--- a/compiler/tests-dynlink-wasm/dune
+++ b/compiler/tests-dynlink-wasm/dune
@@ -54,7 +54,9 @@
 
 (rule
  (target main.out)
- (deps plugin.wasmo)
+ (deps
+  plugin.wasmo
+  (glob_files main.bc.wasm.assets/*))
  (enabled_if %{env:WASM_OF_OCAML=false})
  (action
   (with-outputs-to
@@ -90,7 +92,9 @@
 
 (rule
  (target main_compile_and_load.out)
- (deps plugin_compiled.wasmo)
+ (deps
+  plugin_compiled.wasmo
+  (glob_files main_compile_and_load.bc.wasm.assets/*))
  (enabled_if %{env:WASM_OF_OCAML=false})
  (action
   (with-outputs-to
@@ -115,7 +119,10 @@
 
 (rule
  (target dynlink_loadfile.out)
- (deps plugin.cmo plugin2.cma)
+ (deps
+  plugin.cmo
+  plugin2.cma
+  (glob_files dynlink_loadfile.bc.wasm.assets/*))
  (enabled_if %{env:WASM_OF_OCAML=false})
  (action
   (with-outputs-to
@@ -181,7 +188,12 @@
 
 (rule
  (target dynlink_loadfile_wp.out)
- (deps plugin.cmo plugin2.cma plugin_uses_dep.cmo plugin_js.cmo)
+ (deps
+  plugin.cmo
+  plugin2.cma
+  plugin_uses_dep.cmo
+  plugin_js.cmo
+  (glob_files dynlink_loadfile_wp.assets/*))
  (enabled_if %{env:WASM_OF_OCAML=false})
  (action
   (with-outputs-to
diff --git a/compiler/tests-ocaml/lib-arg/dune b/compiler/tests-ocaml/lib-arg/dune
index 1fee099413..7a856b8d3f 100644
--- a/compiler/tests-ocaml/lib-arg/dune
+++ b/compiler/tests-ocaml/lib-arg/dune
@@ -18,6 +18,8 @@
 (rule
  (target test_rest_all_wasm.ml.corrected)
  (enabled_if %{env:WASM_OF_OCAML=false})
+ (deps
+  (glob_files ../expect_wasm.bc.wasm.assets/*))
  (action
   (run node %{dep:../expect_wasm.bc.wasm.js} %{dep:test_rest_all_wasm.ml})))
 
diff --git a/compiler/tests-ocaml/lib-array/dune b/compiler/tests-ocaml/lib-array/dune
index c281ad438c..ed7265081d 100644
--- a/compiler/tests-ocaml/lib-array/dune
+++ b/compiler/tests-ocaml/lib-array/dune
@@ -16,6 +16,8 @@
 (rule
  (target test_array_wasm.ml.corrected)
  (enabled_if %{env:WASM_OF_OCAML=false})
+ (deps
+  (glob_files ../expect_wasm.bc.wasm.assets/*))
  (action
   (run node %{dep:../expect_wasm.bc.wasm.js} %{dep:test_array_wasm.ml})))
 
diff --git a/compiler/tests-ocaml/lib-either/dune b/compiler/tests-ocaml/lib-either/dune
index febf0dccb0..31e95afd55 100644
--- a/compiler/tests-ocaml/lib-either/dune
+++ b/compiler/tests-ocaml/lib-either/dune
@@ -14,6 +14,8 @@
 (rule
  (target test_wasm.ml.corrected)
  (enabled_if %{env:WASM_OF_OCAML=false})
+ (deps
+  (glob_files ../expect_wasm.bc.wasm.assets/*))
  (action
   (run node %{dep:../expect_wasm.bc.wasm.js} %{dep:test_wasm.ml})))
 
diff --git a/compiler/tests-ocaml/lib-internalformat/dune b/compiler/tests-ocaml/lib-internalformat/dune
index febf0dccb0..31e95afd55 100644
--- a/compiler/tests-ocaml/lib-internalformat/dune
+++ b/compiler/tests-ocaml/lib-internalformat/dune
@@ -14,6 +14,8 @@
 (rule
  (target test_wasm.ml.corrected)
  (enabled_if %{env:WASM_OF_OCAML=false})
+ (deps
+  (glob_files ../expect_wasm.bc.wasm.assets/*))
  (action
   (run node %{dep:../expect_wasm.bc.wasm.js} %{dep:test_wasm.ml})))
 
diff --git a/compiler/tests-ocaml/lib-lazy/dune b/compiler/tests-ocaml/lib-lazy/dune
index febf0dccb0..31e95afd55 100644
--- a/compiler/tests-ocaml/lib-lazy/dune
+++ b/compiler/tests-ocaml/lib-lazy/dune
@@ -14,6 +14,8 @@
 (rule
  (target test_wasm.ml.corrected)
  (enabled_if %{env:WASM_OF_OCAML=false})
+ (deps
+  (glob_files ../expect_wasm.bc.wasm.assets/*))
  (action
   (run node %{dep:../expect_wasm.bc.wasm.js} %{dep:test_wasm.ml})))
 
diff --git a/compiler/tests-predef/dune b/compiler/tests-predef/dune
index 80d7337edf..2ea5508b71 100644
--- a/compiler/tests-predef/dune
+++ b/compiler/tests-predef/dune
@@ -43,6 +43,8 @@
 (rule
  (target main-wasm.out)
  (enabled_if %{env:WASM_OF_OCAML=false})
+ (deps
+  (glob_files main.bc.wasm.assets/*))
  (action
   (with-stdout-to
    %{target}
diff --git a/compiler/tests-toplevel/dune b/compiler/tests-toplevel/dune
index c94fcc24ef..8b0167a94a 100644
--- a/compiler/tests-toplevel/dune
+++ b/compiler/tests-toplevel/dune
@@ -81,6 +81,8 @@
   (and
    %{env:WASM_OF_OCAML=false}
    (>= %{ocaml_version} 5.4)))
+ (deps
+  (glob_files test_toplevel_wasm.bc.wasm.assets/*))
  (action
   (with-stdout-to
    %{target}

From 26bbae6584ff85a6ec01eb18e89ac56d3c1f990f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Wed, 6 May 2026 14:43:25 +0200
Subject: [PATCH 04/14] Tests: declare cmi dependencies for --toplevel rules

Under dune 3.23 sandboxing, rules invoking js_of_ocaml or wasm_of_ocaml
with --toplevel need their .cmi files brought into the sandbox.

For locally built cmis, declare them as deps. For library cmis, add
a cmi_include_dirs.txt rule (mirroring the existing one for toplevel.bc)
that uses ocamlfind to produce -I flags, and pass the result via
read-strings.
---
 compiler/tests-toplevel/dune        | 21 ++++++++++++++++++++
 toplevel/examples/lwt_toplevel/dune | 30 +++++++++++++++++++++++++++++
 toplevel/test/dune                  | 19 ++++++++++++++++++
 3 files changed, 70 insertions(+)

diff --git a/compiler/tests-toplevel/dune b/compiler/tests-toplevel/dune
index 8b0167a94a..2b5d755520 100644
--- a/compiler/tests-toplevel/dune
+++ b/compiler/tests-toplevel/dune
@@ -7,6 +7,15 @@
   (flags :standard --toplevel))
  (modes byte js))
 
+(rule
+ (target cmi_include_dirs.txt)
+ (deps
+  (package js_of_ocaml-compiler))
+ (action
+  (with-stdout-to
+   %{target}
+   (run ocamlfind query -format "-I\n%d" -r js_of_ocaml-compiler.dynlink))))
+
 (rule
  (targets test_toplevel.js)
  (action
@@ -15,6 +24,7 @@
    --toplevel
    -w
    no-missing-effects-backend
+   %{read-strings:cmi_include_dirs.txt}
    %{dep:test_toplevel.bc}
    -o
    %{targets})))
@@ -60,6 +70,16 @@
  (action
   (copy %{dep:test_toplevel.ml} %{target})))
 
+(rule
+ (target cmi_include_dirs_wasm.txt)
+ (deps
+  (package js_of_ocaml-compiler)
+  (package wasm_of_ocaml-compiler))
+ (action
+  (with-stdout-to
+   %{target}
+   (run ocamlfind query -format "-I\n%d" -r wasm_of_ocaml-compiler.dynlink))))
+
 (rule
  (targets
   test_toplevel_wasm.js
@@ -71,6 +91,7 @@
    --toplevel
    -w
    no-missing-effects-backend
+   %{read-strings:cmi_include_dirs_wasm.txt}
    %{dep:test_toplevel_wasm.bc}
    -o
    test_toplevel_wasm.js)))
diff --git a/toplevel/examples/lwt_toplevel/dune b/toplevel/examples/lwt_toplevel/dune
index 70a2b20878..a10f077e8c 100644
--- a/toplevel/examples/lwt_toplevel/dune
+++ b/toplevel/examples/lwt_toplevel/dune
@@ -129,6 +129,7 @@
 
 (rule
  (targets test_dynlink.js)
+ (deps test_dynlink.cmi)
  (action
   (run
    %{bin:js_of_ocaml}
@@ -213,6 +214,33 @@
      (or 0 1)
      (run grep -v ^$))))))
 
+(rule
+ (target cmi_include_dirs.txt)
+ (deps
+  (package js_of_ocaml)
+  (package js_of_ocaml-compiler)
+  (package js_of_ocaml-lwt)
+  (package js_of_ocaml-tyxml)
+  (package js_of_ocaml-toplevel)
+  (package js_of_ocaml-ppx))
+ (action
+  (with-stdout-to
+   %{target}
+   (run
+    ocamlfind
+    query
+    -format
+    "-I\n%d"
+    -r
+    js_of_ocaml-compiler.runtime
+    js_of_ocaml-lwt
+    js_of_ocaml-lwt.graphics
+    js_of_ocaml-tyxml
+    js_of_ocaml-toplevel
+    js_of_ocaml-toplevel.common
+    js_of_ocaml-ppx.as-lib
+    js_of_ocaml.deriving))))
+
 (rule
  (targets toplevel.js)
  ;; Embedding the cmis as JS string literals overflows OCaml's 16 MB
@@ -244,6 +272,7 @@
    --toplevel
    --disable
    shortvar
+   %{read-strings:cmi_include_dirs.txt}
    %{read-strings:javascript_runtime_files.txt}
    %{dep:toplevel.bc}
    -o
@@ -296,6 +325,7 @@
    compile
    --toplevel
    --effects=cps
+   %{read-strings:cmi_include_dirs.txt}
    --file
    %{dep:examples.ml}
    --export
diff --git a/toplevel/test/dune b/toplevel/test/dune
index 6e70b03a15..c6ec5c769b 100644
--- a/toplevel/test/dune
+++ b/toplevel/test/dune
@@ -29,6 +29,24 @@
  (action
   (run jsoo_mkcmis -o %{target} stdlib)))
 
+(rule
+ (target cmi_include_dirs.txt)
+ (deps
+  (package js_of_ocaml)
+  (package js_of_ocaml-toplevel))
+ (action
+  (with-stdout-to
+   %{target}
+   (run
+    ocamlfind
+    query
+    -format
+    "-I\n%d"
+    -r
+    js_of_ocaml-toplevel
+    js_of_ocaml-toplevel.common
+    re))))
+
 (rule
  (targets test_toplevel1.js)
  (action
@@ -41,6 +59,7 @@
    shortvar
    -w
    no-missing-effects-backend
+   %{read-strings:cmi_include_dirs.txt}
    %{dep:test_toplevel1.bc}
    -o
    %{targets})))

From 4ba8962163d0a410bf316ea901a94f0a9e427c34 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Thu, 7 May 2026 10:09:17 +0200
Subject: [PATCH 05/14] Tests: declare wc.ml as a dep of the basic-io test

Under dune 3.23 sandboxing, wc.ml needs to be brought into the
sandbox. Inline the dep with %{dep:wc.ml} on the command line.
---
 compiler/tests-ocaml/basic-io/dune | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/tests-ocaml/basic-io/dune b/compiler/tests-ocaml/basic-io/dune
index 0dda8c0246..f9b55cf681 100644
--- a/compiler/tests-ocaml/basic-io/dune
+++ b/compiler/tests-ocaml/basic-io/dune
@@ -2,4 +2,4 @@
  (names wc)
  (modes js wasm)
  (action
-  (run node %{test} wc.ml)))
+  (run node %{test} %{dep:wc.ml})))

From 58fc72fa2a07838f668659b2288c3177ea952ca8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Tue, 5 May 2026 18:59:56 +0200
Subject: [PATCH 06/14] Switch to dune 3.23.1

It uses `js_of_ocaml --build-config` to manage config details.
---
 VERSION                            | 2 +-
 dune-project                       | 3 ++-
 js_of_ocaml-compiler.opam          | 2 +-
 js_of_ocaml-lwt.opam               | 2 +-
 js_of_ocaml-ppx.opam               | 2 +-
 js_of_ocaml-ppx_deriving_json.opam | 2 +-
 js_of_ocaml-toplevel.opam          | 2 +-
 js_of_ocaml-tyxml.opam             | 2 +-
 js_of_ocaml.opam                   | 2 +-
 wasm_of_ocaml-compiler.opam        | 2 +-
 10 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/VERSION b/VERSION
index 91e4a9f262..ed2ca09d46 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-6.3.2
+6.4.0~alpha~dev
diff --git a/dune-project b/dune-project
index f9f1ce7f50..c094ea3dfd 100644
--- a/dune-project
+++ b/dune-project
@@ -1,4 +1,4 @@
-(lang dune 3.20)
+(lang dune 3.23)
 (using menhir 3.0)
 (using directory-targets 0.1)
 (using oxcaml 0.1)
@@ -19,6 +19,7 @@
  (description
   "Js_of_ocaml is a compiler from OCaml bytecode to JavaScript. It makes it possible to run pure OCaml programs in JavaScript environment like browsers and Node.js")
  (depends
+  (dune (>= 3.23.1))
   (ocaml (and (>= 4.13) (< 5.6)))
   (num :with-test)
   (ppx_expect (and (>= v0.16.1) :with-test))
diff --git a/js_of_ocaml-compiler.opam b/js_of_ocaml-compiler.opam
index 1c7e4f20eb..fe452fa50a 100644
--- a/js_of_ocaml-compiler.opam
+++ b/js_of_ocaml-compiler.opam
@@ -12,7 +12,7 @@ homepage: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 doc: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
 depends: [
-  "dune" {>= "3.20"}
+  "dune" {>= "3.23.1"}
   "ocaml" {>= "4.13" & < "5.6"}
   "num" {with-test}
   "ppx_expect" {>= "v0.16.1" & with-test}
diff --git a/js_of_ocaml-lwt.opam b/js_of_ocaml-lwt.opam
index f40e8cdfa3..8f1a92c410 100644
--- a/js_of_ocaml-lwt.opam
+++ b/js_of_ocaml-lwt.opam
@@ -12,7 +12,7 @@ homepage: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 doc: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
 depends: [
-  "dune" {>= "3.20"}
+  "dune" {>= "3.23"}
   "ocaml" {>= "4.13"}
   "js_of_ocaml" {= version}
   "js_of_ocaml-ppx" {= version}
diff --git a/js_of_ocaml-ppx.opam b/js_of_ocaml-ppx.opam
index dcbe53e82a..67211b0906 100644
--- a/js_of_ocaml-ppx.opam
+++ b/js_of_ocaml-ppx.opam
@@ -12,7 +12,7 @@ homepage: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 doc: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
 depends: [
-  "dune" {>= "3.20"}
+  "dune" {>= "3.23"}
   "ocaml" {>= "4.13"}
   "js_of_ocaml" {= version}
   "ppxlib" {>= "0.33"}
diff --git a/js_of_ocaml-ppx_deriving_json.opam b/js_of_ocaml-ppx_deriving_json.opam
index dcbe53e82a..67211b0906 100644
--- a/js_of_ocaml-ppx_deriving_json.opam
+++ b/js_of_ocaml-ppx_deriving_json.opam
@@ -12,7 +12,7 @@ homepage: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 doc: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
 depends: [
-  "dune" {>= "3.20"}
+  "dune" {>= "3.23"}
   "ocaml" {>= "4.13"}
   "js_of_ocaml" {= version}
   "ppxlib" {>= "0.33"}
diff --git a/js_of_ocaml-toplevel.opam b/js_of_ocaml-toplevel.opam
index ba4ff91426..d015eb6da9 100644
--- a/js_of_ocaml-toplevel.opam
+++ b/js_of_ocaml-toplevel.opam
@@ -12,7 +12,7 @@ homepage: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 doc: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
 depends: [
-  "dune" {>= "3.20"}
+  "dune" {>= "3.23"}
   "ocaml" {>= "4.13"}
   "js_of_ocaml-compiler" {= version}
   "ocamlfind" {>= "1.5.1"}
diff --git a/js_of_ocaml-tyxml.opam b/js_of_ocaml-tyxml.opam
index 2ce14c0b6b..3d44b79d35 100644
--- a/js_of_ocaml-tyxml.opam
+++ b/js_of_ocaml-tyxml.opam
@@ -12,7 +12,7 @@ homepage: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 doc: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
 depends: [
-  "dune" {>= "3.20"}
+  "dune" {>= "3.23"}
   "ocaml" {>= "4.13"}
   "js_of_ocaml" {= version}
   "js_of_ocaml-ppx" {= version}
diff --git a/js_of_ocaml.opam b/js_of_ocaml.opam
index 4158595584..5b91479de1 100644
--- a/js_of_ocaml.opam
+++ b/js_of_ocaml.opam
@@ -12,7 +12,7 @@ homepage: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 doc: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
 depends: [
-  "dune" {>= "3.20"}
+  "dune" {>= "3.23"}
   "ocaml" {>= "4.13"}
   "js_of_ocaml-compiler" {= version}
   "num" {with-test}
diff --git a/wasm_of_ocaml-compiler.opam b/wasm_of_ocaml-compiler.opam
index 2577bd563f..56582758a2 100644
--- a/wasm_of_ocaml-compiler.opam
+++ b/wasm_of_ocaml-compiler.opam
@@ -12,7 +12,7 @@ homepage: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 doc: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
 depends: [
-  "dune" {>= "3.20"}
+  "dune" {>= "3.23"}
   "ocaml" {>= "4.14"}
   "js_of_ocaml" {= version}
   "num" {with-test}

From d546b3688962bce086a5687619f2c5fb42244fae Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Thu, 21 May 2026 21:03:54 +0200
Subject: [PATCH 07/14] CI: drop dune version constraint from
 oxcaml-dune-patches

oxcaml-dune-patches pins dune <= 3.21, but the project requires
dune >= 3.23. opam re-checks dependency constraints on every install,
so a one-shot --ignore-constraints-on=dune flag isn't enough.

Re-pin the package with the dune version constraint stripped, so
subsequent installs let dune resolve to 3.23.x normally.
---
 .github/workflows/js_of_ocaml.yml   | 13 +++++++++++++
 .github/workflows/wasm_of_ocaml.yml | 13 +++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/.github/workflows/js_of_ocaml.yml b/.github/workflows/js_of_ocaml.yml
index 640fa0f95c..589ef2efb3 100644
--- a/.github/workflows/js_of_ocaml.yml
+++ b/.github/workflows/js_of_ocaml.yml
@@ -168,6 +168,19 @@ jobs:
           opam pin add opam-core -n 2.5.1+ox
         if: ${{ endsWith(matrix.ocaml-compiler, '+ox') }}
 
+      # oxcaml-dune-patches pins dune <= 3.21, but the project requires
+      # dune >= 3.23. Re-pin the package with the dune version constraint
+      # stripped — opam re-checks dependency constraints on every install,
+      # so a one-shot --ignore-constraints-on flag isn't enough.
+      - name: Drop dune version constraint from oxcaml-dune-patches (OxCaml)
+        if: ${{ endsWith(matrix.ocaml-compiler, '+ox') }}
+        run: |
+          DIR=$(mktemp -d)
+          opam show --raw oxcaml-dune-patches \
+            | perl -0777 -pe 's/"dune"\s+\{build & \([^)]+\)\}/"dune" {build}/' \
+            > "$DIR/oxcaml-dune-patches.opam"
+          opam pin add oxcaml-dune-patches "$DIR" -k path -n -y
+
       - run: opam install . --deps-only --with-test
         # Install the test dependencies
         if: ${{ !matrix.skip-test }}
diff --git a/.github/workflows/wasm_of_ocaml.yml b/.github/workflows/wasm_of_ocaml.yml
index 3d879d9ca4..08dae5c1cc 100644
--- a/.github/workflows/wasm_of_ocaml.yml
+++ b/.github/workflows/wasm_of_ocaml.yml
@@ -141,6 +141,19 @@ jobs:
           opam pin add sedlex -n 3.6+ox
         if: ${{ endsWith(matrix.ocaml-compiler, '+ox') }}
 
+      # oxcaml-dune-patches pins dune <= 3.21, but the project requires
+      # dune >= 3.23. Re-pin the package with the dune version constraint
+      # stripped — opam re-checks dependency constraints on every install,
+      # so a one-shot --ignore-constraints-on flag isn't enough.
+      - name: Drop dune version constraint from oxcaml-dune-patches (OxCaml)
+        if: ${{ endsWith(matrix.ocaml-compiler, '+ox') }}
+        run: |
+          DIR=$(mktemp -d)
+          opam show --raw oxcaml-dune-patches \
+            | perl -0777 -pe 's/"dune"\s+\{build & \([^)]+\)\}/"dune" {build}/' \
+            > "$DIR/oxcaml-dune-patches.opam"
+          opam pin add oxcaml-dune-patches "$DIR" -k path -n -y
+
       # Add some packaged to the opam invariant;
       # opam makes wrong choices otherwise
       - name: Hold some packages

From efa6a27d7906621de73d1c2079f8ef44b824e044 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Fri, 16 Jan 2026 15:50:00 +0100
Subject: [PATCH 08/14] Update nodejs options

---
 tools/node_wrapper.ml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/node_wrapper.ml b/tools/node_wrapper.ml
index 0a3826fd7c..5f6bffb7cf 100644
--- a/tools/node_wrapper.ml
+++ b/tools/node_wrapper.ml
@@ -1,4 +1,4 @@
-let extra_args_for_wasoo = [ "--stack-size=10000" ]
+let extra_args_for_wasoo = [ "--experimental-wasm-wasmfx"; "--stack-size=10000" ]
 
 let extra_args_for_jsoo = []
 

From bfa8859b659b52cc43fa69cd861fddc11e88c839 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Thu, 19 Feb 2026 13:27:51 +0100
Subject: [PATCH 09/14] Update Wasm linker to support stack switching
 instructions

---
 compiler/lib-wasm/link.ml      | 15 ++++++-
 compiler/lib-wasm/wasm_link.ml | 71 +++++++++++++++++++++++++++++-----
 2 files changed, 75 insertions(+), 11 deletions(-)

diff --git a/compiler/lib-wasm/link.ml b/compiler/lib-wasm/link.ml
index 6df7065435..f2753de927 100644
--- a/compiler/lib-wasm/link.ml
+++ b/compiler/lib-wasm/link.ml
@@ -193,7 +193,20 @@ module Wasm_binary = struct
 
   let reftype' i ch =
     match i with
-    | 0x6a | 0x6b | 0x6c | 0x6d | 0x6e | 0x6f | 0x70 | 0x71 | 0x72 | 0x73 -> ()
+    | 0x68
+    | 0x69
+    | 0x6a
+    | 0x6b
+    | 0x6c
+    | 0x6d
+    | 0x6e
+    | 0x6f
+    | 0x70
+    | 0x71
+    | 0x72
+    | 0x73
+    | 0x74
+    | 0x75 -> ()
     | 0x63 | 0x64 -> heaptype ch
     | _ ->
         Format.eprintf "Unknown reftype %x@." i;
diff --git a/compiler/lib-wasm/wasm_link.ml b/compiler/lib-wasm/wasm_link.ml
index 8502268a11..02fa54e1ca 100644
--- a/compiler/lib-wasm/wasm_link.ml
+++ b/compiler/lib-wasm/wasm_link.ml
@@ -23,6 +23,10 @@ type heaptype =
   | Nofunc
   | Extern
   | Noextern
+  | Exn
+  | Noexn
+  | Cont
+  | Nocont
   | Any
   | Eq
   | I31
@@ -66,6 +70,7 @@ type comptype =
       }
   | Struct of fieldtype array
   | Array of fieldtype
+  | Cont of int
 
 type subtype =
   { final : bool
@@ -164,6 +169,8 @@ module Write = struct
 
   let heaptype st ch typ =
     match (typ : heaptype) with
+    | Nocont -> byte ch 0x75
+    | Noexn -> byte ch 0x74
     | Nofunc -> byte ch 0x73
     | Noextern -> byte ch 0x72
     | None_ -> byte ch 0x71
@@ -174,6 +181,8 @@ module Write = struct
     | I31 -> byte ch 0x6C
     | Struct -> byte ch 0x6B
     | Array -> byte ch 0x6A
+    | Exn -> byte ch 0x69
+    | Cont -> byte ch 0x68
     | Type idx -> sint ch (typeidx st idx)
 
   let reftype st ch { nullable; typ } =
@@ -219,6 +228,9 @@ module Write = struct
         byte ch 1;
         uint ch (typeidx st supertype));
     match typ with
+    | Cont idx ->
+        byte ch 0x5D;
+        sint ch (typeidx st idx)
     | Array field_type ->
         byte ch 0x5E;
         fieldtype st ch field_type
@@ -571,7 +583,9 @@ module Read = struct
   let heaptype st ch =
     let i = sint ch in
     match i + 128 with
-    | 0X73 -> Nofunc
+    | 0x75 -> Nocont
+    | 0x74 -> Noexn
+    | 0x73 -> Nofunc
     | 0x72 -> Noextern
     | 0x71 -> None_
     | 0x70 -> Func
@@ -581,6 +595,8 @@ module Read = struct
     | 0x6C -> I31
     | 0x6B -> Struct
     | 0x6A -> Array
+    | 0x69 -> Exn
+    | 0x68 -> Cont
     | _ ->
         if i < 0 then failwith (Printf.sprintf "Unknown heaptype %x@." i);
         let i =
@@ -598,7 +614,9 @@ module Read = struct
 
   let reftype' st i ch =
     match i with
-    | 0X73 -> nullable Nofunc
+    | 0x75 -> nullable Nocont
+    | 0x74 -> nullable Noexn
+    | 0x73 -> nullable Nofunc
     | 0x72 -> nullable Noextern
     | 0x71 -> nullable None_
     | 0x70 -> nullable Func
@@ -608,6 +626,8 @@ module Read = struct
     | 0x6C -> nullable I31
     | 0x6B -> nullable Struct
     | 0x6A -> nullable Array
+    | 0x69 -> nullable Exn
+    | 0x68 -> nullable Cont
     | 0x63 -> nullable (heaptype st ch)
     | 0x64 -> { nullable = false; typ = heaptype st ch }
     | _ -> failwith (Printf.sprintf "Unknown reftype %x@." i)
@@ -654,6 +674,14 @@ module Read = struct
 
   let comptype st i ch =
     match i with
+    | 0x5D ->
+        let i = sint ch in
+        let i =
+          if i >= st.type_index_count
+          then lnot (i - st.type_index_count)
+          else st.type_mapping.(i)
+        in
+        Cont i
     | 0x5E -> Array (fieldtype st ch)
     | 0x5F -> Struct (vec (fieldtype st) ch)
     | 0x60 ->
@@ -1260,6 +1288,13 @@ module Scan = struct
       | 0xD1 (* ref.is_null *) | 0xD3 (* ref.eq *) | 0xD4 (* ref.as_non_null *) ->
           pos + 1 |> instructions
       | 0xD2 (* ref.func *) -> pos + 1 |> funcidx |> instructions
+      | 0xE0 (* cont.new *) -> pos + 1 |> typeidx |> instructions
+      | 0xE1 (* cont.bind *) -> pos + 1 |> typeidx |> typeidx |> instructions
+      | 0xE2 (* suspend *) -> pos + 1 |> tagidx |> instructions
+      | 0xE3 (* resume *) -> pos + 1 |> typeidx |> vector on_clause |> instructions
+      | 0xE4 (* resume_throw *) ->
+          pos + 1 |> typeidx |> tagidx |> vector on_clause |> instructions
+      | 0xE5 (* switch *) -> pos + 1 |> typeidx |> tagidx |> instructions
       | 0xFB -> pos + 1 |> gc_instruction
       | 0xFC -> (
           if debug then Format.eprintf "  %d@." (get (pos + 1));
@@ -1393,7 +1428,12 @@ module Scan = struct
       match get pos with
       | 0 (* catch *) | 1 (* catch_ref *) -> pos + 1 |> tagidx |> labelidx
       | 2 (* catch_all *) | 3 (* catch_all_ref *) -> pos + 1 |> labelidx
-      | c -> failwith (Printf.sprintf "bad catch 0x02%d@." c)
+      | c -> failwith (Printf.sprintf "bad catch 0x%02x@." c)
+    and on_clause pos =
+      match get pos with
+      | 0 (* on *) -> pos + 1 |> tagidx |> labelidx
+      | 1 (* on .. switch *) -> pos + 1 |> tagidx
+      | c -> failwith (Printf.sprintf "bad on clause 0x%02x@." c)
     and block_end pos =
       if debug then Format.eprintf "0x%02X (@%d) block end@." (get pos) pos;
       match get pos with
@@ -1552,6 +1592,10 @@ let heap_subtype (subtyping_info : subtype array) (ty : heaptype) (ty' : heaptyp
   | Nofunc, Nofunc
   | (Extern | Noextern), Extern
   | Noextern, Noextern
+  | (Exn | Noexn), Exn
+  | Noexn, Noexn
+  | (Cont | Nocont), Cont
+  | Nocont, Nocont
   | (Any | Eq | I31 | Struct | Array | None_), Any
   | (Eq | I31 | Struct | Array | None_), Eq
   | (I31 | None_), I31
@@ -1561,27 +1605,35 @@ let heap_subtype (subtyping_info : subtype array) (ty : heaptype) (ty' : heaptyp
   | Type i, (Any | Eq) -> (
       match subtyping_info.(i).typ with
       | Struct _ | Array _ -> true
-      | Func _ -> false)
+      | Func _ | Cont _ -> false)
   | Type i, Struct -> (
       match subtyping_info.(i).typ with
       | Struct _ -> true
-      | Array _ | Func _ -> false)
+      | Array _ | Func _ | Cont _ -> false)
   | Type i, Array -> (
       match subtyping_info.(i).typ with
       | Array _ -> true
-      | Struct _ | Func _ -> false)
+      | Struct _ | Func _ | Cont _ -> false)
   | Type i, Func -> (
       match subtyping_info.(i).typ with
       | Func _ -> true
-      | Struct _ | Array _ -> false)
+      | Struct _ | Array _ | Cont _ -> false)
+  | Type i, Cont -> (
+      match subtyping_info.(i).typ with
+      | Cont _ -> true
+      | Struct _ | Array _ | Func _ -> false)
   | None_, Type i -> (
       match subtyping_info.(i).typ with
       | Struct _ | Array _ -> true
-      | Func _ -> false)
+      | Func _ | Cont _ -> false)
   | Nofunc, Type i -> (
       match subtyping_info.(i).typ with
       | Func _ -> true
-      | Struct _ | Array _ -> false)
+      | Struct _ | Array _ | Cont _ -> false)
+  | Nocont, Type i -> (
+      match subtyping_info.(i).typ with
+      | Cont _ -> true
+      | Struct _ | Array _ | Func _ -> false)
   | Type i, Type i' -> subtype subtyping_info i i'
   | _ -> false
 
@@ -2465,7 +2517,6 @@ let f files ~output_file =
 (*
 LATER
 - testsuite : import/export matching, source maps, multiple start functions, ...
-- missing instructions ==> typed continuations (?)
 - check features?
 
 MAYBE

From 1373b35255276fadf103d988e03036ceb5e9aa5d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Sun, 24 Mar 2024 12:57:09 +0100
Subject: [PATCH 10/14] Effects based on Stack Switching proposal

---
 compiler/bin-wasm_of_ocaml/cmd_arg.ml   |  20 +-
 compiler/bin-wasm_of_ocaml/compile.ml   |   1 +
 compiler/bin-wasm_of_ocaml/link_wasm.ml |  36 +++-
 compiler/lib-wasm/binaryen.ml           |   5 +
 compiler/lib-wasm/generate.ml           |   2 +-
 compiler/lib-wasm/link.ml               |   2 +-
 compiler/lib/build_info.ml              |   4 +-
 compiler/lib/config.ml                  |   3 +-
 compiler/lib/config.mli                 |   1 +
 compiler/lib/driver.ml                  |   8 +-
 compiler/lib/effects.ml                 |   2 +-
 compiler/lib/generate.ml                |   8 +-
 compiler/lib/generate_closure.ml        |   2 +-
 compiler/lib/inline.ml                  |   2 +-
 compiler/lib/js_output.ml               |   2 +-
 compiler/lib/linker.ml                  |   4 +-
 compiler/lib/partial_cps_analysis.ml    |   2 +-
 compiler/lib/specialize_js.ml           |   2 +-
 compiler/lib/unit_info.ml               |   2 +-
 runtime/wasm/effect-native.wat          | 254 ++++++++++++++++++++++++
 runtime/wasm/effect.wat                 |   2 +-
 runtime/wasm/stdlib.wat                 |  10 +
 22 files changed, 339 insertions(+), 35 deletions(-)
 create mode 100644 runtime/wasm/effect-native.wat

diff --git a/compiler/bin-wasm_of_ocaml/cmd_arg.ml b/compiler/bin-wasm_of_ocaml/cmd_arg.ml
index e6c8602f6b..15df070b82 100644
--- a/compiler/bin-wasm_of_ocaml/cmd_arg.ml
+++ b/compiler/bin-wasm_of_ocaml/cmd_arg.ml
@@ -38,7 +38,7 @@ let trim_trailing_dir_sep s =
 
 let normalize_include_dirs dirs = List.map dirs ~f:trim_trailing_dir_sep
 
-let normalize_effects (effects : [ `Disabled | `Cps | `Jspi ] option) common :
+let normalize_effects (effects : [ `Disabled | `Cps | `Jspi | `Native ] option) common :
     Config.effects_backend =
   match effects with
   | None ->
@@ -47,7 +47,7 @@ let normalize_effects (effects : [ `Disabled | `Cps | `Jspi ] option) common :
       if List.mem ~eq:String.equal "effects" common.Jsoo_cmdline.Arg.optim.enable
       then `Cps
       else `Jspi
-  | Some ((`Disabled | `Cps | `Jspi) as e) -> e
+  | Some ((`Disabled | `Cps | `Jspi | `Native) as e) -> e
 
 type t =
   { common : Jsoo_cmdline.Arg.t
@@ -182,11 +182,15 @@ let options () =
   let effects =
     let doc =
       "Select an implementation of effect handlers. [$(docv)] should be one of $(b,jspi) \
-       (the default), $(b,cps), or $(b,disabled)."
+       (the default), $(b,cps), $(b,native) or $(b,disabled)."
     in
     Arg.(
       value
-      & opt (some (enum [ "jspi", `Jspi; "cps", `Cps; "disabled", `Disabled ])) None
+      & opt
+          (some
+             (enum
+                [ "jspi", `Jspi; "cps", `Cps; "native", `Native; "disabled", `Disabled ]))
+          None
       & info [ "effects" ] ~docv:"KIND" ~doc)
   in
   let build_t
@@ -330,11 +334,15 @@ let options_runtime_only () =
   let effects =
     let doc =
       "Select an implementation of effect handlers. [$(docv)] should be one of $(b,jspi) \
-       (the default), $(b,cps), or $(b,disabled)."
+       (the default), $(b,cps), $(b,native) or $(b,disabled)."
     in
     Arg.(
       value
-      & opt (some (enum [ "jspi", `Jspi; "cps", `Cps; "disabled", `Disabled ])) None
+      & opt
+          (some
+             (enum
+                [ "jspi", `Jspi; "cps", `Cps; "native", `Native; "disabled", `Disabled ]))
+          None
       & info [ "effects" ] ~docv:"KIND" ~doc)
   in
   let build_config = Jsoo_cmdline.Arg.build_config in
diff --git a/compiler/bin-wasm_of_ocaml/compile.ml b/compiler/bin-wasm_of_ocaml/compile.ml
index 73d6df565b..5a3b3e1702 100644
--- a/compiler/bin-wasm_of_ocaml/compile.ml
+++ b/compiler/bin-wasm_of_ocaml/compile.ml
@@ -83,6 +83,7 @@ let preprocessor_variables () =
         (match Config.effects () with
         | `Disabled | `Jspi -> "jspi"
         | `Cps -> "cps"
+        | `Native -> "native"
         | `Double_translation -> assert false) )
   ]
 
diff --git a/compiler/bin-wasm_of_ocaml/link_wasm.ml b/compiler/bin-wasm_of_ocaml/link_wasm.ml
index 07032da073..47e185b2f2 100644
--- a/compiler/bin-wasm_of_ocaml/link_wasm.ml
+++ b/compiler/bin-wasm_of_ocaml/link_wasm.ml
@@ -32,6 +32,7 @@ type options =
   ; variables : Preprocess.variables
   ; allowed_imports : string list option
   ; binaryen_options : binaryen_options
+  ; effects_backend : Js_of_ocaml_compiler.Config.effects_backend
   }
 
 let options =
@@ -71,13 +72,30 @@ let options =
     let allowed_imports =
       if List.is_empty allowed_imports then None else Some (List.concat allowed_imports)
     in
-    `Ok
-      { input_modules
-      ; output_file
-      ; variables
-      ; allowed_imports
-      ; binaryen_options = { common; opt; merge }
-      }
+    let effects_backend =
+      match
+        List.find_map
+          ~f:(fun (k, v) -> if String.equal k "effects" then Some v else None)
+          variables.Preprocess.set
+      with
+      | Some "native" -> Ok (`Native : Js_of_ocaml_compiler.Config.effects_backend)
+      | Some "cps" -> Ok `Cps
+      | Some "jspi" | None -> Ok `Jspi
+      | Some "double-translation" -> Ok `Double_translation
+      | Some "disabled" -> Ok `Disabled
+      | Some other -> Error other
+    in
+    match effects_backend with
+    | Ok effects_backend ->
+        `Ok
+          { input_modules
+          ; output_file
+          ; variables
+          ; allowed_imports
+          ; binaryen_options = { common; opt; merge }
+          ; effects_backend
+          }
+    | Error other -> `Error (false, Printf.sprintf "unknown effects backend %s" other)
   in
   let t =
     Term.(
@@ -98,7 +116,11 @@ let link
     ; variables
     ; allowed_imports
     ; binaryen_options = { common; merge; opt }
+    ; effects_backend
     } =
+  (* So that the --enable-stack-switching option is passed to Binaryen
+     tools for native effects. *)
+  Js_of_ocaml_compiler.Config.set_effects_backend effects_backend;
   let inputs =
     List.map
       ~f:(fun (module_name, file) -> { Wat_preprocess.module_name; file; source = File })
diff --git a/compiler/lib-wasm/binaryen.ml b/compiler/lib-wasm/binaryen.ml
index 1089330ef2..0420f95aa9 100644
--- a/compiler/lib-wasm/binaryen.ml
+++ b/compiler/lib-wasm/binaryen.ml
@@ -40,6 +40,11 @@ let common_options () =
     ; "--enable-strings"
     ]
   in
+  let l =
+    match Config.effects () with
+    | `Native -> "--enable-stack-switching" :: l
+    | `Disabled | `Jspi | `Cps | `Double_translation -> l
+  in
   let l = if Config.Flag.pretty () then "-g" :: l else l in
   let l = if times () then "--no-validation" :: l else l in
   l
diff --git a/compiler/lib-wasm/generate.ml b/compiler/lib-wasm/generate.ml
index 024ce84c0c..7844c78027 100644
--- a/compiler/lib-wasm/generate.ml
+++ b/compiler/lib-wasm/generate.ml
@@ -26,7 +26,7 @@ let times = Debug.find "times"
 let effects_cps () =
   match Config.effects () with
   | `Cps -> true
-  | `Disabled | `Jspi -> false
+  | `Disabled | `Jspi | `Native -> false
   | `Double_translation -> assert false
 
 module Generate (Target : Target_sig.S) = struct
diff --git a/compiler/lib-wasm/link.ml b/compiler/lib-wasm/link.ml
index f2753de927..04661f1940 100644
--- a/compiler/lib-wasm/link.ml
+++ b/compiler/lib-wasm/link.ml
@@ -563,7 +563,7 @@ let build_runtime_arguments
   let props =
     match Config.effects () with
     | `Disabled -> ("disable_effects", Javascript.EBool true) :: props
-    | `Jspi | `Cps -> props
+    | `Jspi | `Cps | `Native -> props
     | `Double_translation -> assert false
   in
   let props =
diff --git a/compiler/lib/build_info.ml b/compiler/lib/build_info.ml
index eba95dfd9e..7ce27c1831 100644
--- a/compiler/lib/build_info.ml
+++ b/compiler/lib/build_info.ml
@@ -41,12 +41,14 @@ let string_of_effects_backend : Config.effects_backend -> string = function
   | `Cps -> "cps"
   | `Double_translation -> "double-translation"
   | `Jspi -> "jspi"
+  | `Native -> "native"
 
 let effects_backend_of_string = function
   | "disabled" -> `Disabled
   | "cps" -> `Cps
   | "double-translation" -> `Double_translation
   | "jspi" -> `Jspi
+  | "native" -> `Native
   | _ -> invalid_arg "effects_backend_of_string"
 
 type config_key =
@@ -73,7 +75,7 @@ let config_keys target =
         ( [ "disabled"; "cps"; "double-translation" ]
         , fun () -> string_of_effects_backend (Config.effects ()) )
     | `Wasm ->
-        ( [ "disabled"; "cps"; "jspi" ]
+        ( [ "disabled"; "cps"; "jspi"; "native" ]
         , fun () -> string_of_effects_backend (Config.effects ()) )
   in
   [ Enum_key
diff --git a/compiler/lib/config.ml b/compiler/lib/config.ml
index 69db92887d..e95dd673ce 100644
--- a/compiler/lib/config.ml
+++ b/compiler/lib/config.ml
@@ -236,6 +236,7 @@ type effects_backend =
   | `Cps
   | `Double_translation
   | `Jspi
+  | `Native
   ]
 
 let effects_ : [< `None | effects_backend ] ref = ref `None
@@ -243,7 +244,7 @@ let effects_ : [< `None | effects_backend ] ref = ref `None
 let effects () =
   match !effects_ with
   | `None -> failwith "effects was not set"
-  | (`Jspi | `Cps | `Disabled | `Double_translation) as b -> b
+  | (`Jspi | `Cps | `Native | `Disabled | `Double_translation) as b -> b
 
 let set_effects_backend (backend : effects_backend) =
   effects_ := (backend :> [ `None | effects_backend ])
diff --git a/compiler/lib/config.mli b/compiler/lib/config.mli
index 2a540f68bc..d9f0fe2a4b 100644
--- a/compiler/lib/config.mli
+++ b/compiler/lib/config.mli
@@ -128,6 +128,7 @@ type effects_backend =
   | `Cps
   | `Double_translation
   | `Jspi
+  | `Native
   ]
 
 val effects : unit -> effects_backend
diff --git a/compiler/lib/driver.ml b/compiler/lib/driver.ml
index 5573acae27..bb712eee16 100644
--- a/compiler/lib/driver.ml
+++ b/compiler/lib/driver.ml
@@ -178,7 +178,7 @@ let effects_and_exact_calls
         | `JavaScript -> Lambda_lifting.f p
       in
       p, trampolined_calls, in_cps, None, shapes
-  | `Disabled | `Jspi ->
+  | `Disabled | `Jspi | `Native ->
       let p =
         Specialize.f
           ~shape:(fun f ->
@@ -719,9 +719,9 @@ let optimize ~shapes ~profile ~keep_flow_data p =
     +> map_fst5
          (match Config.target (), Config.effects () with
          | `JavaScript, `Disabled -> Generate_closure.f
-         | `JavaScript, (`Cps | `Double_translation) | `Wasm, (`Disabled | `Jspi | `Cps)
-           -> Fun.id
-         | `JavaScript, `Jspi | `Wasm, `Double_translation -> assert false)
+         | `JavaScript, (`Cps | `Double_translation)
+         | `Wasm, (`Disabled | `Jspi | `Cps | `Native) -> Fun.id
+         | `JavaScript, (`Jspi | `Native) | `Wasm, `Double_translation -> assert false)
     +> map_fst5 deadcode'
   in
   if times () then Format.eprintf "Start Optimizing...@.";
diff --git a/compiler/lib/effects.ml b/compiler/lib/effects.ml
index 30d8765fca..c6e7c928ae 100644
--- a/compiler/lib/effects.ml
+++ b/compiler/lib/effects.ml
@@ -40,7 +40,7 @@ let debug = Debug.find "effects"
 
 let double_translate () =
   match Config.effects () with
-  | `Disabled | `Jspi -> assert false
+  | `Disabled | `Jspi | `Native -> assert false
   | `Cps -> false
   | `Double_translation -> true
 
diff --git a/compiler/lib/generate.ml b/compiler/lib/generate.ml
index fb540469b7..151a4c0ff5 100644
--- a/compiler/lib/generate.ml
+++ b/compiler/lib/generate.ml
@@ -28,7 +28,7 @@ let cps_transform () =
   match Config.effects () with
   | `Cps | `Double_translation -> true
   | `Disabled -> false
-  | `Jspi -> assert false
+  | `Jspi | `Native -> assert false
 
 open Code
 module J = Javascript
@@ -1092,7 +1092,7 @@ let apply_fun_raw =
             (* Effects enabled, CPS version, not single-version *)
             J.EDot (f, J.ANormal, cps_field)
         | `Cps | `Double_translation | `Disabled -> f
-        | `Jspi -> assert false
+        | `Jspi | `Native -> assert false
       in
       (* We skip the arity check when we know that we have the right
          number of parameters, since this test is expensive. *)
@@ -1119,7 +1119,7 @@ let apply_fun_raw =
                  (match Config.effects () with
                  | `Double_translation when cps -> "caml_call_gen_cps"
                  | `Double_translation | `Cps | `Disabled -> "caml_call_gen"
-                 | `Jspi -> assert false))
+                 | `Jspi | `Native -> assert false))
               [ f; J.array params ]
               J.N )
     in
@@ -1135,7 +1135,7 @@ let apply_fun_raw =
                 [ apply ~cps:false f (fst (List.take (n - 1) params)) ]
                 J.N )
       | `Double_translation | `Cps | `Disabled -> apply ~cps f params
-      | `Jspi -> assert false
+      | `Jspi | `Native -> assert false
     in
     if trampolined
     then (
diff --git a/compiler/lib/generate_closure.ml b/compiler/lib/generate_closure.ml
index 659a5a6479..34bc2b775f 100644
--- a/compiler/lib/generate_closure.ml
+++ b/compiler/lib/generate_closure.ml
@@ -337,7 +337,7 @@ let f p : Code.program =
 let f p =
   assert (
     match Config.effects () with
-    | `Disabled | `Jspi -> true
+    | `Disabled | `Jspi | `Native -> true
     | `Cps | `Double_translation -> false);
   let open Config.Param in
   match tailcall_optim () with
diff --git a/compiler/lib/inline.ml b/compiler/lib/inline.ml
index 6da3837a9f..f7546a58e8 100644
--- a/compiler/lib/inline.ml
+++ b/compiler/lib/inline.ml
@@ -454,7 +454,7 @@ and should_inline ~context info args =
         || (not (Lazy.force !(context.has_closures)))
            && Option.equal Var.equal info.enclosing_function context.enclosing_function
     | `Wasm, _ | `JavaScript, `Double_translation -> true
-    | `JavaScript, `Jspi -> assert false)
+    | `JavaScript, (`Jspi | `Native) -> assert false)
   && (functor_like ~context info
      || (context.live_vars.(Var.idx info.f) = 1
         &&
diff --git a/compiler/lib/js_output.ml b/compiler/lib/js_output.ml
index 47b7d44f51..3b33f9c80a 100644
--- a/compiler/lib/js_output.ml
+++ b/compiler/lib/js_output.ml
@@ -2229,7 +2229,7 @@ let program ?(accept_unnamed_var = false) ?(source_map = false) f p =
   PP.set_needed_space_function f need_space;
   (match Config.effects () with
   | `Cps | `Double_translation -> PP.set_adjust_indentation_function f (fun n -> n mod 40)
-  | `Disabled | `Jspi | (exception Failure _) -> ());
+  | `Disabled | `Jspi | `Native | (exception Failure _) -> ());
   PP.start_group f 0;
   O.program f p;
   PP.end_group f;
diff --git a/compiler/lib/linker.ml b/compiler/lib/linker.ml
index 1fbc0f90ed..d17823cb60 100644
--- a/compiler/lib/linker.ml
+++ b/compiler/lib/linker.ml
@@ -205,13 +205,13 @@ module Fragment = struct
       ; ( "effects"
         , fun () ->
             match Config.effects () with
-            | `Disabled | `Jspi -> false
+            | `Disabled | `Jspi | `Native -> false
             | `Cps | `Double_translation -> true )
       ; ( "doubletranslate"
         , fun () ->
             match Config.effects () with
             | `Double_translation -> true
-            | `Jspi | `Cps | `Disabled -> false )
+            | `Jspi | `Cps | `Native | `Disabled -> false )
       ; ( "wasm"
         , fun () ->
             match Config.target () with
diff --git a/compiler/lib/partial_cps_analysis.ml b/compiler/lib/partial_cps_analysis.ml
index 262711ad31..657df406af 100644
--- a/compiler/lib/partial_cps_analysis.ml
+++ b/compiler/lib/partial_cps_analysis.ml
@@ -24,7 +24,7 @@ let times = Debug.find "times"
 
 let double_translate () =
   match Config.effects () with
-  | `Disabled | `Jspi -> assert false
+  | `Disabled | `Jspi | `Native -> assert false
   | `Cps -> false
   | `Double_translation -> true
 
diff --git a/compiler/lib/specialize_js.ml b/compiler/lib/specialize_js.ml
index 2d19410f84..ecbba2d1e5 100644
--- a/compiler/lib/specialize_js.ml
+++ b/compiler/lib/specialize_js.ml
@@ -553,7 +553,7 @@ let f_once_after p =
     match Config.target (), Config.effects () with
     | `JavaScript, `Disabled -> true
     | `JavaScript, (`Cps | `Double_translation) | `Wasm, _ -> false
-    | `JavaScript, `Jspi -> assert false
+    | `JavaScript, (`Jspi | `Native) -> assert false
   in
   let f = function
     | Let (x, Closure (l, (pc, []), _)) as i -> (
diff --git a/compiler/lib/unit_info.ml b/compiler/lib/unit_info.ml
index cd64c12a14..3ec1fa77c4 100644
--- a/compiler/lib/unit_info.ml
+++ b/compiler/lib/unit_info.ml
@@ -56,7 +56,7 @@ let of_cmo (cmo : Ocaml_compiler.Cmo_format.t) =
   let requires = Global_name.Compunit_set.diff requires provides in
   let effects_without_cps =
     (match Config.effects () with
-      | `Disabled | `Jspi -> true
+      | `Disabled | `Jspi | `Native -> true
       | `Cps | `Double_translation -> false)
     && List.exists (Cmo_format.primitives cmo) ~f:(function
       | "%resume" | "%reperform" | "%perform" | "%with_stack" | "%with_stack_bind" -> true
diff --git a/runtime/wasm/effect-native.wat b/runtime/wasm/effect-native.wat
new file mode 100644
index 0000000000..2c23675259
--- /dev/null
+++ b/runtime/wasm/effect-native.wat
@@ -0,0 +1,254 @@
+;; Wasm_of_ocaml runtime support
+;; http://www.ocsigen.org/js_of_ocaml/
+;;
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU Lesser General Public License as published by
+;; the Free Software Foundation, with linking exception;
+;; either version 2.1 of the License, or (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU Lesser General Public License for more details.
+;;
+;; You should have received a copy of the GNU Lesser General Public License
+;; along with this program; if not, write to the Free Software
+;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+(module
+(@if (= effects "native")
+(@then
+   (import "fail" "caml_raise_constant"
+      (func $caml_raise_constant (param (ref eq))))
+   (import "fail" "caml_raise_with_arg"
+      (func $caml_raise_with_arg (param $tag (ref eq)) (param $arg (ref eq))))
+   (import "obj" "caml_fresh_oo_id"
+     (func $caml_fresh_oo_id (param (ref eq)) (result (ref eq))))
+   (import "obj" "cont_tag" (global $cont_tag i32))
+   (import "obj" "object_tag" (global $object_tag i32))
+   (import "stdlib" "caml_named_value"
+      (func $caml_named_value (param (ref eq)) (result (ref null eq))))
+   (import "fail" "ocaml_exception" (tag $ocaml_exception (param (ref eq))))
+   (import "fail" "javascript_exception"
+      (tag $javascript_exception (param externref)))
+   (import "jslib" "caml_wrap_exception"
+      (func $caml_wrap_exception (param externref) (result (ref eq))))
+   (import "stdlib" "caml_main_wrapper"
+      (global $caml_main_wrapper (mut (ref null $wrapper_func))))
+   (import "effect" "effect_allowed" (global $effect_allowed (mut i32)))
+
+   (type $block (array (mut (ref eq))))
+   (type $bytes (array (mut i8)))
+   (type $function_1 (func (param (ref eq) (ref eq)) (result (ref eq))))
+   (type $closure (sub (struct (;(field i32);) (field (ref $function_1)))))
+   (type $function_3
+      (func (param (ref eq) (ref eq) (ref eq) (ref eq)) (result (ref eq))))
+   (type $closure_3
+      (sub $closure
+         (struct (field (ref $function_1)) (field (ref $function_3)))))
+
+   ;; Effect types
+
+   (tag $effect (param (ref eq)) (result (ref eq) (ref eq)))
+
+   (type $cont_function (func (param (ref eq) (ref eq)) (result (ref eq))))
+
+   (type $cont (cont $cont_function))
+
+   (type $generic_fiber
+      (sub
+         (struct
+            (field $value (mut (ref eq)))
+            (field $exn (mut (ref eq)))
+            (field $effect (mut (ref eq))))))
+
+   (type $fiber
+      (sub final $generic_fiber
+         (struct
+            (field $value (mut (ref eq)))
+            (field $exn (mut (ref eq)))
+            (field $effect (mut (ref eq)))
+            (field $cont (mut (ref $cont))))))
+
+   ;; Unhandled effects
+
+   (@string $effect_unhandled "Effect.Unhandled")
+
+   (func $raise_unhandled
+      (param $eff (ref eq)) (param (ref eq)) (result (ref eq))
+      (block $null
+         (call $caml_raise_with_arg
+            (br_on_null $null
+               (call $caml_named_value (global.get $effect_unhandled)))
+            (local.get $eff)))
+      (call $caml_raise_constant
+         (array.new_fixed $block 3 (ref.i31 (global.get $object_tag))
+            (global.get $effect_unhandled)
+            (call $caml_fresh_oo_id (ref.i31 (i32.const 0)))))
+      (ref.i31 (i32.const 0)))
+
+   (global $raise_unhandled (ref $closure)
+      (struct.new $closure (ref.func $raise_unhandled)))
+
+   (type $func (func (result (ref eq))))
+   (type $wrapper_func (func (param (ref $func))))
+   (type $func_closure (struct (field (ref $func))))
+
+   (func $wrapper_cont
+      (param $f (ref eq)) (param (ref eq)) (result (ref eq))
+      (return_call_ref $func
+         (local.get $f)
+         (struct.get $func_closure 0
+            (ref.cast (ref $func_closure) (local.get $f)))))
+
+   (func $unhandled_effect_wrapper (param $start (ref $func))
+      (local $cont (ref $cont))
+      (local $f (ref eq)) (local $v (ref eq))
+      (local $resume_res (tuple (ref eq) (ref $cont)))
+      (local.set $cont (cont.new $cont (ref.func $wrapper_cont)))
+      (local.set $f (struct.new $func_closure (local.get $start)))
+      (local.set $v (ref.i31 (i32.const 0)))
+      (loop $loop
+         (local.set $resume_res
+            (block $handle_effect (result (ref eq) (ref $cont))
+               (resume $cont (on $effect $handle_effect)
+                  (local.get $f) (local.get $v) (local.get $cont))
+               (return)))
+         (local.set $cont (tuple.extract 2 1 (local.get $resume_res)))
+         (local.set $v (tuple.extract 2 0 (local.get $resume_res)))
+         (local.set $f (global.get $raise_unhandled))
+         (br $loop)))
+
+   (func $init
+      (global.set $caml_main_wrapper (ref.func $unhandled_effect_wrapper)))
+
+   (start $init)
+
+   ;; Resume
+
+   (@string $already_resumed "Effect.Continuation_already_resumed")
+
+   (func $resume (export "%resume")
+      (param $vfiber (ref eq)) (param $f (ref eq)) (param $v (ref eq))
+      (param $tail (ref eq)) (result (ref eq))
+      (local $fiber (ref $fiber))
+      (local $res (ref eq))
+      (local $exn (ref eq))
+      (local $resume_res (tuple (ref eq) (ref $cont)))
+      (if (ref.eq (local.get $vfiber) (ref.i31 (i32.const 0)))
+         (then
+            (call $caml_raise_constant
+               (ref.as_non_null
+                  (call $caml_named_value (global.get $already_resumed))))))
+      (local.set $fiber (ref.cast (ref $fiber) (local.get $vfiber)))
+      (local.set $exn
+         (block $handle_exception (result (ref eq))
+            (local.set $resume_res
+               (block $handle_effect (result (ref eq) (ref $cont))
+                  (local.set $res
+                     (try (result (ref eq))
+                        (do
+                           (resume $cont
+                               (on $effect $handle_effect)
+                               (local.get $f) (local.get $v)
+                               (struct.get $fiber $cont (local.get $fiber))))
+                        (catch $javascript_exception
+                           (br $handle_exception
+                              (call $caml_wrap_exception (pop externref))))
+                        (catch $ocaml_exception
+                           (br $handle_exception (pop (ref eq))))))
+                  ;; handle return
+                  (return_call_ref $function_1 (local.get $res)
+                     (local.tee $f
+                        (struct.get $fiber $value (local.get $fiber)))
+                     (struct.get $closure 0
+                        (ref.cast (ref $closure) (local.get $f))))))
+            ;; handle effect
+            (struct.set $fiber $cont (local.get $fiber)
+               (tuple.extract 2 1 (local.get $resume_res)))
+            (return_call_ref $function_3
+               (tuple.extract 2 0 (local.get $resume_res))
+               (array.new_fixed $block 3 (ref.i31 (global.get $cont_tag))
+                  (local.get $fiber)
+                  (local.get $fiber))
+               (if (result (ref eq))
+                     (ref.eq (local.get $tail) (ref.i31 (i32.const 0)))
+                  (then (local.get $fiber))
+                  (else (local.get $tail)))
+               (local.tee $f
+                  (struct.get $fiber $effect (local.get $fiber)))
+               (struct.get $closure_3 1
+                  (ref.cast (ref $closure_3) (local.get $f))))))
+      ;; handle exception
+      (return_call_ref $function_1 (local.get $exn)
+         (local.tee $f
+            (struct.get $fiber $exn (local.get $fiber)))
+         (struct.get $closure 0 (ref.cast (ref $closure) (local.get $f)))))
+
+   ;; Perform
+
+   (func (export "%reperform")
+      (param $eff (ref eq)) (param $cont (ref eq)) (param $tail (ref eq))
+      (result (ref eq))
+      (local $res (tuple (ref eq) (ref eq)))
+      (local.set $res (suspend $effect (local.get $eff)))
+      (return_call $resume
+         (ref.as_non_null
+            (array.get $block
+               (ref.cast (ref $block) (local.get $cont))
+               (i32.const 1)))
+         (tuple.extract 2 0 (local.get $res))
+         (tuple.extract 2 1 (local.get $res))
+         (local.get $tail)))
+
+   (func (export "%perform") (param $eff (ref eq)) (result (ref eq))
+      (local $res (tuple (ref eq) (ref eq)))
+      (if (i32.eqz (global.get $effect_allowed))
+         (then
+            (return_call $raise_unhandled
+               (local.get $eff) (ref.i31 (i32.const 0)))))
+      (local.set $res (suspend $effect (local.get $eff)))
+      (return_call_ref $function_1 (tuple.extract 2 1 (local.get $res))
+         (tuple.extract 2 0 (local.get $res))
+         (struct.get $closure 0
+            (ref.cast (ref $closure) (tuple.extract 2 0 (local.get $res))))))
+
+   ;; Allocate a stack
+
+   (func $initial_cont
+      (param $f (ref eq)) (param $x (ref eq)) (result (ref eq))
+      (return_call_ref $function_1 (local.get $x)
+         (local.get $f)
+         (struct.get $closure 0 (ref.cast (ref $closure) (local.get $f)))))
+
+   (func (export "caml_alloc_stack")
+      (param $hv (ref eq)) (param $hx (ref eq)) (param $hf (ref eq))
+      (result (ref eq))
+      (struct.new $fiber
+         (local.get $hv) (local.get $hx) (local.get $hf)
+         (cont.new $cont (ref.func $initial_cont))))
+
+   (func (export "%with_stack")
+      (param $hv (ref eq)) (param $hx (ref eq)) (param $hf (ref eq))
+      (param $f (ref eq)) (param $v (ref eq))
+      (result (ref eq))
+      (return_call $resume
+         (struct.new $fiber
+            (local.get $hv) (local.get $hx) (local.get $hf)
+            (cont.new $cont (ref.func $initial_cont)))
+         (local.get $f) (local.get $v)
+         (ref.i31 (i32.const 0))))
+
+   (func (export "%with_stack_bind")
+      (param $hv (ref eq)) (param $hx (ref eq)) (param $hf (ref eq))
+      (param $dyn (ref eq)) (param $bind (ref eq))
+      (param $f (ref eq)) (param $v (ref eq))
+      (result (ref eq))
+      (return_call $resume
+         (struct.new $fiber
+            (local.get $hv) (local.get $hx) (local.get $hf)
+            (cont.new $cont (ref.func $initial_cont)))
+         (local.get $f) (local.get $v)
+         (ref.i31 (i32.const 0))))
+))
+)
diff --git a/runtime/wasm/effect.wat b/runtime/wasm/effect.wat
index 4cbcda2c10..f314f1c9d8 100644
--- a/runtime/wasm/effect.wat
+++ b/runtime/wasm/effect.wat
@@ -81,7 +81,7 @@
    (global $raise_unhandled (ref $closure)
       (struct.new $closure (ref.func $raise_unhandled)))
 
-   (global $effect_allowed (mut i32) (i32.const 1))
+   (global $effect_allowed (export "effect_allowed") (mut i32) (i32.const 1))
 
    (func $caml_continuation_use_noexc (export "caml_continuation_use_noexc")
       (param (ref eq)) (result (ref eq))
diff --git a/runtime/wasm/stdlib.wat b/runtime/wasm/stdlib.wat
index b0e7708d91..88ca67e8d5 100644
--- a/runtime/wasm/stdlib.wat
+++ b/runtime/wasm/stdlib.wat
@@ -455,11 +455,21 @@
       (global.set $uncaught_exception (local.get $exn))
       (call $caml_main (ref.func $reraise_exception)))
 
+   (type $wrapper_func (func (param (ref $func))))
+   (global $caml_main_wrapper (export "caml_main_wrapper")
+      (mut (ref null $wrapper_func))
+      (ref.null $wrapper_func))
+
    (func $caml_main (export "caml_main") (param $start (ref func))
       (local $exn (ref eq))
       (local $msg (ref eq))
       (try
          (do
+            (block $fallback
+               (call_ref $wrapper_func
+                  (ref.cast (ref $func) (local.get $start))
+                  (br_on_null $fallback (global.get $caml_main_wrapper)))
+               (return))
             (drop (call_ref $func (ref.cast (ref $func) (local.get $start)))))
          (catch $ocaml_exit)
          (catch $ocaml_exception

From f3948bfe3f87ba6974fcc155227e86007e2004e0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Fri, 20 Feb 2026 19:15:08 +0100
Subject: [PATCH 11/14] Add dune profile for native effects

---
 compiler/tests-linkall/dune |  2 ++
 dune                        | 11 +++++++++++
 2 files changed, 13 insertions(+)

diff --git a/compiler/tests-linkall/dune b/compiler/tests-linkall/dune
index dbfe6e4c78..6132a16e81 100644
--- a/compiler/tests-linkall/dune
+++ b/compiler/tests-linkall/dune
@@ -13,6 +13,8 @@
 (test
  (name test)
  (modes byte js wasm)
+ (enabled_if
+  (<> %{profile} with-native-effects))
  (libraries dynlink)
  ;; It doesn't seem possible to create a pack-ed module with dune.
  ;; However, dynlink uses pack to embed a copy
diff --git a/dune b/dune
index 7c368168b7..3632c2121b 100644
--- a/dune
+++ b/dune
@@ -36,6 +36,17 @@
   (binaries
    (tools/node_wrapper.exe as node)
    (tools/node_wrapper.exe as node.exe)))
+ (with-native-effects
+  (js_of_ocaml
+   ;; Native effects is not supported in js
+   (enabled_if false))
+  (wasm_of_ocaml
+   (compilation_mode separate)
+   (flags
+    (:standard --effects native)))
+  (binaries
+   (tools/node_wrapper.exe as node)
+   (tools/node_wrapper.exe as node.exe)))
  (bench_no_debug
   (flags
    (:standard \ -g))

From 33088f4eb98108c8f5418858306dbbe217b0222d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Fri, 20 Feb 2026 19:15:15 +0100
Subject: [PATCH 12/14] Update CI

---
 .github/workflows/wasm_of_ocaml.yml | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/wasm_of_ocaml.yml b/.github/workflows/wasm_of_ocaml.yml
index 08dae5c1cc..311b4171eb 100644
--- a/.github/workflows/wasm_of_ocaml.yml
+++ b/.github/workflows/wasm_of_ocaml.yml
@@ -101,7 +101,7 @@ jobs:
       - name: Set-up Node.js
         uses: actions/setup-node@v6
         with:
-          node-version: latest
+          node-version: ${{ matrix.os == 'windows-latest' && 'latest' || 'v26.0.0-v8-canary20260216631fb6e5ef' }}
 
       - name: Set-up OCaml ${{ matrix.ocaml-compiler }}
         uses: ocaml/setup-ocaml@v3
@@ -205,6 +205,11 @@ jobs:
         working-directory: ./wasm_of_ocaml
         run: opam exec -- dune build @runtest-wasm --profile with-effects
 
+      - name: Run tests with native effects
+        if: ${{ matrix.ocaml-compiler >= '5.' && matrix.separate_compilation && matrix.os != 'windows-latest' }}
+        working-directory: ./wasm_of_ocaml
+        run: opam exec -- dune build @runtest-wasm --profile with-native-effects
+
       - name: Run Base tests
         if: matrix.all_jane_street_tests
         continue-on-error: ${{ matrix.os == 'windows-latest' }}

From 2380cc85efc1a8511f0262dc02354202e652d4c3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Sun, 24 Mar 2024 12:57:09 +0100
Subject: [PATCH 13/14] Document update: native effects

---
 manual/effects.wiki       | 13 +++++++++++++
 manual/options.wiki       |  1 +
 manual/wasm_overview.wiki |  8 +++++++-
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/manual/effects.wiki b/manual/effects.wiki
index 2bd6742489..ae36c19e69 100644
--- a/manual/effects.wiki
+++ b/manual/effects.wiki
@@ -21,6 +21,19 @@ Since CPS code is usually slower, this can avoid performance degradations. You c
 also ensure that some code runs in direct style using
 <<a_api subproject="js_of_ocaml-compiler"|val Jsoo_runtime.Effect.assume_no_perform>>.
 
+==@@id="wasm"@@ Wasm_of_ocaml
+
+Wasm_of_ocaml provides three effect handler implementations:
+
+* **{{{--effects=jspi}}}** (default) uses the JavaScript-Promise Integration extension.
+  It does not require any code transformation but requires a runtime that supports JSPI.
+* **{{{--effects=cps}}}** uses the same CPS transformation as js_of_ocaml.
+* **{{{--effects=native}}}** uses the
+  [[https://github.com/WebAssembly/stack-switching|WebAssembly Stack Switching proposal]]
+  (typed continuations). It provides the best performance but requires a runtime with
+  support for the WasmFX extension (currently available in V8/Node.js behind the
+  {{{--experimental-wasm-wasmfx}}} flag).
+
 ==@@id="dune"@@ Dune integration
 
 Dune is aware of the {{{--effects}}} option. You can add it to the
diff --git a/manual/options.wiki b/manual/options.wiki
index 78d8309662..3a0fd87c3d 100644
--- a/manual/options.wiki
+++ b/manual/options.wiki
@@ -45,6 +45,7 @@ For **js_of_ocaml** (default: {{{disabled}}}):
 For **wasm_of_ocaml** (default: {{{jspi}}}):
 * **{{{jspi}}}** - JavaScript-Promise Integration (default). Available in Chrome 137, Node.js 25, and higher. Use {{{cps}}} for other browsers. Performing effects is slower than with {{{cps}}}.
 * **{{{cps}}}** - CPS transformation for effect support
+* **{{{native}}}** - WebAssembly stack switching (wasm_of_ocaml only, requires WasmFX runtime support)
 * **{{{disabled}}}** - No effect handler support
 
 See <<a_manual chapter="effects"|Effect handlers>> for details.
diff --git a/manual/wasm_overview.wiki b/manual/wasm_overview.wiki
index 3424d75571..f8f9ae54a8 100644
--- a/manual/wasm_overview.wiki
+++ b/manual/wasm_overview.wiki
@@ -68,16 +68,22 @@ Compared to js_of_ocaml:
 
 === Effect handlers
 
-OCaml 5.x code using effect handlers can be compiled in two ways:
+OCaml 5.x code using effect handlers can be compiled in three ways:
 
 * **{{{--effects=cps}}}** - Uses the CPS transformation from js_of_ocaml
 * **{{{--effects=jspi}}}** (default) - Uses the [[https://github.com/WebAssembly/js-promise-integration|JavaScript-Promise Integration extension]]
+* **{{{--effects=native}}}** - Uses the [[https://github.com/WebAssembly/stack-switching|WebAssembly Stack Switching proposal]]
 
 The CPS transformation is not the default since the generated code is slower,
 larger, and less readable. However, the JSPI extension is currently only
 available in Chrome 137 and Node.js 25 (or higher), and performing effects
 is slower when using it. Use {{{--effects=cps}}} for other browsers.
 
+The native implementation is based on the WebAssembly typed continuations
+proposal (stack switching). It provides the best performance but requires a
+runtime with support for the WasmFX extension (currently available in
+V8/Node.js behind the {{{--experimental-wasm-wasmfx}}} flag).
+
 ==@@id="js-bindings"@@ Binding with JavaScript libraries
 
 Js_of_ocaml lets you bind code with JavaScript libraries by linking {{{.js}}} files.

From 747e3b617763b3146b8c515cce5fb75f84315728 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Vouillon?= <jerome.vouillon@gmail.com>
Date: Thu, 26 Feb 2026 14:29:32 +0100
Subject: [PATCH 14/14] Changes

---
 CHANGES.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGES.md b/CHANGES.md
index 41c4aeeb9b..068af7d303 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -14,6 +14,7 @@
 * Lib: add `Performance` module (#2221)
 * Put more values into global variables (#2211)
 * Runtime: intial support for quickjs-ng
+* Wasm_of_ocaml: alternative effect implementation based on the Stack Switching proposal (#2189)
 
 ## Bug fixes
 * Compiler: fix reference unboxing (#2210)