Enabling --enable-gc-assertions under gcc 4.6.2 in Mac OS X 10.7 causes all tests to fail. The reason is the assertion in GC_add_roots_inner that tests whether the address is on an word size 8 byte boundary. But the linker generated address "start" can fail that test, and it's added in GC_dyld_image_add. The value was 0x100122a44.