[llvm-dev] greendragon build noisy due to mmap_stress.cc

[Dmitry Vyukov via llvm-dev]

On Fri, Jan 22, 2016 at 4:11 PM, Kuba Brecka <jbrecka at apple.com> wrote:
> Hm, I tried to reproduce this as well, but unsuccessfully.  From the crash
> report:  EXC_I386_GPFLT means we’re dereferencing a non-canonical pointer,
> in this case “0x00486000000025df”.  This happens at wrap_OSSpinLockLock+17,
> which is just after the prologue and just after calling cur_thread().  So
> I’d say it happens when we’re dereferencing the pointer returned by
> cur_thread().  On OS X, we’re doing this trick where we store the
> ThreadState pointer in the shadow memory.  Could it be that something
> actually read/wrote the memory that is backed by the same place as the
> shadow memory?
>
> Does “0x00486000000025df” like a reasonable content of a shadow cell?



Yes, it looks like a reasonable shadow:

// Shadow (from most significant bit):
//   freed           : 1
//   tid             : kTidBits
//   is_atomic       : 1
//   is_read         : 1
//   size_log        : 2
//   addr0           : 3
//   epoch           : kClkBits