From 2ec1c359d90f20472e5800b5d1d8441dd22c1c73 Mon Sep 17 00:00:00 2001
From: Luite Stegeman <stegeman@gmail.com>
Date: Tue, 31 Jan 2023 16:58:28 +0900
Subject: Fix marking async exceptions in the JS backend

Async exceptions are posted as a pair of the exception and
the thread object. This fixes the marking pass to correctly
follow the two elements of the pair.

Potentially fixes #22836

(cherry picked from commit 77a8234c5d284846e18c0a44ba5ee196059aaea6)
---
 rts/js/gc.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/rts/js/gc.js b/rts/js/gc.js
index 6c9934ed33..00def79daa 100644
--- a/rts/js/gc.js
+++ b/rts/js/gc.js
@@ -493,7 +493,8 @@ function h$follow(obj, sp) {
 		    }
                 }
 		for(i=0;i<c.excep.length;i++) {
-		    ADDW(c.excep[i]);
+		    ADDW(c.excep[i][0]); // the posting thread
+		    ADDW(c.excep[i][1]); // the exception
 		}
             } else if(c instanceof h$Transaction) {
                 // - the accessed TVar values don't need to be marked
-- 
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