[asan] Initialize fake stack during thread init

[waltl]

Summary

If detect-stack-use-after-return is on, initialize fake stack during
AsanThread::Init(), rather than lazily. This is required on Myriad.
From kcc: "There used to be a reason why this was done lazily, but I
don't remember if we still have that reason." Tested on x86.

[vitalybuka]

I'd guess the reason is that thread may run only non instrumented code and it will never use fake stack

[vitalybuka]

Also https://reviews.llvm.org/rL184934

compiler-rt/trunk/lib/asan/asan_thread.h

return !atomic_load(&stack_switching_, memory_order_relaxed) &&
            (reinterpret_cast<uptr>(fake_stack_) > 1);
   }
 
   FakeStack *fake_stack() {
     if (!__asan_option_detect_stack_use_after_return)
       return nullptr;
     if (atomic_load(&stack_switching_, memory_order_relaxed))
       return nullptr;
-    if (!has_fake_stack())
-      return AsyncSignalSafeLazyInitFakeStack();
     return fake_stack_;
   }
 
   // True is this thread is currently unwinding stack (i.e. collecting a stack
   // trace). Used to prevent deadlocks on platforms where libc unwinder calls
   // malloc internally. See PR17116 for more details.
   bool isUnwinding() const { return unwinding_; }
   void setUnwinding(bool b) { unwinding_ = b; }

compiler-rt/trunk/lib/asan/asan_thread.cc

if (atomic_compare_exchange_strong(
     return fake_stack_;
   }
   return nullptr;
 }
 
 void AsanThread::Init(const InitOptions *options) {
   next_stack_top_ = next_stack_bottom_ = 0;
   atomic_store(&stack_switching_, false, memory_order_release);
-  fake_stack_ = nullptr;  // Will be initialized lazily if needed.
   CHECK_EQ(this->stack_size(), 0U);
   SetThreadStackAndTls(options);
   CHECK_GT(this->stack_size(), 0U);
   CHECK(AddrIsInMem(stack_bottom_));
   CHECK(AddrIsInMem(stack_top_ - 1));
   ClearShadowForThreadStackAndTLS();
+  fake_stack_ = nullptr;
+  if (__asan_option_detect_stack_use_after_return)
+    AsyncSignalSafeLazyInitFakeStack();
   int local = 0;
   VReport(1, "T%d: stack [%p,%p) size 0x%zx; local=%p\n", tid(),
           (void *)stack_bottom_, (void *)stack_top_, stack_top_ - stack_bottom_,
           &local);
 }
 
 // Fuchsia doesn't use ThreadStart.
 // asan_fuchsia.c defines CreateMainThread and SetThreadStackAndTls.