[libunwind] 71fbd6e - Exit unwinding early when at the top of the stack and additional info won't be found.

[Sterling Augustine via cfe-commits]

Author: Sterling Augustine
Date: 2020-04-02T10:52:25-07:00
New Revision: 71fbd6e40632f437049215904c28ad9d63cff4bc

URL: https://github.com/llvm/llvm-project/commit/71fbd6e40632f437049215904c28ad9d63cff4bc
DIFF: https://github.com/llvm/llvm-project/commit/71fbd6e40632f437049215904c28ad9d63cff4bc.diff

LOG: Exit unwinding early when at the top of the stack and additional info won't be found.

Summary:
This patch follows libgcc's lead: When the return-address register is
zero, there won't be additional stack frames to examine, or gather
information about. Exit before spending time looking for something
known not to be found.

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77099

Added: 
    

Modified: 
    libunwind/src/UnwindCursor.hpp

Removed: 
    


################################################################################
diff  --git a/libunwind/src/UnwindCursor.hpp b/libunwind/src/UnwindCursor.hpp
index e7fb70cc5718..32d71c2c1ed3 100644
--- a/libunwind/src/UnwindCursor.hpp
+++ b/libunwind/src/UnwindCursor.hpp
@@ -1848,6 +1848,12 @@ void UnwindCursor<A, R>::setInfoBasedOnIPRegister(bool isReturnAddress) {
   pc &= (pint_t)~0x1;
 #endif
 
+  // Exit early if at the top of the stack.
+  if (pc == 0) {
+    _unwindInfoMissing = true;
+    return;
+  }
+
   // If the last line of a function is a "throw" the compiler sometimes
   // emits no instructions after the call to __cxa_throw.  This means
   // the return address is actually the start of the next function.