[asan] Add AsanThread::Restart() to support thread restart

[waltl]

Summary

Thread restart is a feature on RTEMS where a thread may resume at an
arbitrary function entry point, but the stack and TLS state are reset.
Use AsanThread::Restart() to do the corresponding bookeeping.

[kcc]

compiler-rt/lib/asan/asan_thread.cc

118 ↗

(On Diff #145283)

add a comment explaining why we need Restart

[waltl]

Address CR comments.

[vitalybuka]

Who is going to call Restart() ?

[waltl]

It's called by __sanitizer_thread_start_hook() defined in asan_rtems.cc (See https://reviews.llvm.org/D46468), which in turn will be call by RTEMS, in the code that starts/restarts a thread.

[alekseyshl]

compiler-rt/lib/asan/asan_thread.cc

120 ↗

(On Diff #145475)

withbut -> without

124 ↗

(On Diff #145475)

Since this feature is very much RTEMS specific, maybe it's better to be kept in asan_rtems.cc? Stack bounds are exposed via thread->GetStackBounds().

[waltl]

Address CR comments

[waltl]

compiler-rt/lib/asan/asan_thread.cc

124 ↗

(On Diff #145475)

The problem is thread->GetStackBounds() is private. I moved the definition of AsanThread::Restart() to asan_rtems.cc, but I still need the declaration in asan_thread.h. Let me know what you think.

[alekseyshl]

Ah, right, it is private. Use stack_top() and stack_bottom() then, they are public.

[waltl]

In D46466#1103420, @alekseyshl wrote:

Ah, right, it is private. Use stack_top() and stack_bottom() then, they are public.

Right. Sorry I missed that. Done, and that makes this patch obsolete.

compiler-rt/lib/asan/asan_thread.h

public:
   void DeleteFakeStack(int tid) {
     if (!fake_stack_) return;
     FakeStack *t = fake_stack_;
     fake_stack_ = nullptr;
     SetTLSFakeStack(nullptr);
     t->Destroy(tid);
   }
 
+  // Used to support thread restart on RTEMS.
+  void Restart();
+
   void StartSwitchFiber(FakeStack **fake_stack_save, uptr bottom, uptr size);
   void FinishSwitchFiber(FakeStack *fake_stack_save, uptr *bottom_old,
                          uptr *size_old);
 
   bool has_fake_stack() {
     return !atomic_load(&stack_switching_, memory_order_relaxed) &&
            (reinterpret_cast<uptr>(fake_stack_) > 1);
   }