diff -r 52462bc541a3 rpython/translator/c/gc.py
--- a/rpython/translator/c/gc.py	Wed May 08 15:23:23 2019 +0200
+++ b/rpython/translator/c/gc.py	Fri May 10 09:17:44 2019 +0300
@@ -461,10 +461,10 @@
         raise Exception("gc_pop_roots should be removed by postprocess_graph")

     def OP_GC_ENTER_ROOTS_FRAME(self, funcgen, op):
-        return '%s += sizeof(pypy_ss_t);' % (funcgen.gcpol_ss,)
+        return '(char*)(%s) += sizeof(pypy_ss_t);' % (funcgen.gcpol_ss,)

     def OP_GC_LEAVE_ROOTS_FRAME(self, funcgen, op):
-        return '%s -= sizeof(pypy_ss_t);' % (funcgen.gcpol_ss,)
+        return '(char*)(%s) -= sizeof(pypy_ss_t);' % (funcgen.gcpol_ss,)

     def OP_GC_SAVE_ROOT(self, funcgen, op):
         num = op.args[0].value