Fix gc_setmark size for strings (#20361)

Fix #20360

src/gc.c

@@ -607,7 +607,7 @@ static inline uint16_t gc_setmark_pool(jl_ptls_t ptls, jl_taggedvalue_t *o,
 }
 
 static inline uint16_t gc_setmark(jl_ptls_t ptls, jl_value_t *v,
-                                  int sz, uintptr_t tag)
+                                  size_t sz, uintptr_t tag)
 {
     assert(!gc_marked(tag));
     jl_taggedvalue_t *o = jl_astaggedvalue(v);

test/core.jl

@@ -4616,3 +4616,30 @@ end
 
 # issue #19963
 @test_nowarn ccall(:jl_free, Void, (Ptr{Void}, ), C_NULL)
+
+# Wrong string size on 64bits for large string.
+if Sys.WORD_SIZE == 64
+    @noinline function test_large_string20360(slot)
+        try
+            # Do no touch the string to avoid triggering OOM
+            slot[] = Base._string_n(2^32)
+            gc(false)
+        catch ex
+            # This can happen if there's a virtual address size limit
+            @test isa(ex, OutOfMemoryError)
+            @test_broken false
+        end
+        return
+    end
+    @noinline function tester20360()
+        gc()
+        # Makes sure the string is rooted during the `gc(false)`
+        # but is not before the last gc in this function.
+        slot = Ref{Any}()
+        test_large_string20360(slot)
+        slot[] = nothing
+        gc()
+        return
+    end
+    @test_nowarn tester20360()
+end