I had a look at armv6m yesterday evening, parts of my code run fine in gdb, the code crashes in the init of a procedure when trying to prepare the access to contents of a set. The address of the set seems to get calculated totally wrong ending up in a memory access at the end of the chip's address range. Not sure if this is related to your problem, I will try to boil down the example to a bare minimum to see where the generated code differs between armv7m and armv6m.