Don't allow chaos mode to choose a memory range that overlaps where l…

…ibrrpage.so will go.

With reasonably high frequency, chaos mode will map libdl.so into a range that overlaps where librrpage.so should go. This succeeds, because libdl is mapped in first. Later we'll map in librrpage.so with MAP_FIXED and stomp on libdl.so's data pages causing more chaos than we were hoping for.

src/AddressSpace.cc

@@ -2141,6 +2141,9 @@ static MemoryRange choose_global_exclusion_range() {
 remote_ptr<void> AddressSpace::chaos_mode_find_free_memory(RecordTask* t,
  size_t len) {
  static MemoryRange global_exclusion_range = choose_global_exclusion_range();
+ // NB: Above RR_PAGE_ADDR is probably not free anyways, but if it somehow is
+ // don't hand it out again.
+ static MemoryRange rrpage_so_range = MemoryRange(RR_PAGE_ADDR - page_size(), RR_PAGE_ADDR + page_size());
 
  int bits = random_addr_bits(t->arch());
  uint64_t addr_space_limit = uint64_t(1) << bits;
@@ -2194,6 +2197,9 @@ remote_ptr<void> AddressSpace::chaos_mode_find_free_memory(RecordTask* t,
  continue;
  }
  MemoryRange r(addr, ceil_page_size(len));
+ if (r.intersects(rrpage_so_range)) {
+ continue;
+ }
  if (r.intersects(global_exclusion_range)) {
  continue;
  }