[PATCH] D69893: libunwind: Evaluating DWARF operation DW_OP_pick is broken

[kamlesh kumar via Phabricator via cfe-commits]

kamleshbhalui created this revision.
kamleshbhalui added a reviewer: phosek.
Herald added subscribers: libcxx-commits, ldionne, christof.
kamleshbhalui edited the summary of this revision.

reg is unsigned type and used here for getting array element from the end  by negating it.
negation of unsigned can result in large number and array access with that index will result in segmentation
 fault.
As a Fix we cast reg to int then negate it.
Fixes this. 
https://bugs.llvm.org/show_bug.cgi?id=43872


Repository:
  rUNW libunwind

https://reviews.llvm.org/D69893

Files:
  libunwind/src/DwarfInstructions.hpp


Index: libunwind/src/DwarfInstructions.hpp
===================================================================
--- libunwind/src/DwarfInstructions.hpp
+++ libunwind/src/DwarfInstructions.hpp
@@ -430,7 +430,7 @@
       // pick from
       reg = addressSpace.get8(p);
       p += 1;
-      value = sp[-reg];
+      value = sp[-(int)reg];
       *(++sp) = value;
       if (log)
         fprintf(stderr, "duplicate %d in stack\n", reg);


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