From 859ad934bc3b92125043c3e599492aecd3586992 Mon Sep 17 00:00:00 2001
From: Mike Pall <mike>
Date: Sat, 11 Jul 2026 14:37:49 +0200
Subject: x64: Fix callback result handling.

Reported by Matt Gerassimoff.
---
 src/lj_ccallback.c | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'src/lj_ccallback.c')

diff --git a/src/lj_ccallback.c b/src/lj_ccallback.c
index 3ddb7ca5c..2fa8e7ce0 100644
--- a/src/lj_ccallback.c
+++ b/src/lj_ccallback.c
@@ -519,6 +519,10 @@ static void callback_conv_result(CTState *cts, lua_State *L, TValue *o)
 #if LJ_TARGET_X86
     if (ctype_isfp(ctr->info))
       cts->cb.gpr[2] = ctr->size == sizeof(float) ? 1 : 2;
+#elif LJ_TARGET_X64
+    /* Always zero-extend results to 64 bits. */
+    if (ctr->size <= 4 && ctype_isinteger_or_bool(ctr->info))
+      *(uint64_t *)dp = (uint64_t)*(uint32_t *)dp;
 #endif
   }
 }
-- 
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