start_block      2927 gc/os_dep.c        struct hblk * start_block;
start_block      2938 gc/os_dep.c        start_block = (struct hblk *)((word)addr & ~(GC_page_size - 1));
start_block      2941 gc/os_dep.c        for (h = start_block; h <= end_block; h++) {
start_block      2946 gc/os_dep.c        UNPROTECT(start_block,
start_block      2947 gc/os_dep.c        	      ((ptr_t)end_block - (ptr_t)start_block) + HBLKSIZE);