[Lldb-commits] [lldb] 42a9c0c - [lldb] Reland "Fix UB in half2float" to fix the ubsan bot.

[Raphael Isemann via lldb-commits]

Author: Raphael Isemann
Date: 2021-05-24T15:23:32+02:00
New Revision: 42a9c0c80c23fa0de3e3b00fef0dfa6d85e18e55

URL: https://github.com/llvm/llvm-project/commit/42a9c0c80c23fa0de3e3b00fef0dfa6d85e18e55
DIFF: https://github.com/llvm/llvm-project/commit/42a9c0c80c23fa0de3e3b00fef0dfa6d85e18e55.diff

LOG: [lldb] Reland "Fix UB in half2float" to fix the ubsan bot.

This relands part of the UB fix in 4b074b49be206306330076b9fa40632ef1960823.
The original commit also added some additional tests that uncovered some
other issues (see D102845). I landed all the passing tests in
48780527dd6820698f3537f5ebf76499030ee349 and this patch is now just fixing
the UB in half2float. See D102846 for a proposed rewrite of the function.

Original commit message:

  The added DumpDataExtractorTest uncovered that this is lshifting a negative
  integer which upsets ubsan and breaks the sanitizer bot. This patch just
  changes the variable we shift to be unsigned.

Added: 
    

Modified: 
    lldb/source/Core/DumpDataExtractor.cpp

Removed: 
    


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diff  --git a/lldb/source/Core/DumpDataExtractor.cpp b/lldb/source/Core/DumpDataExtractor.cpp
index ec44e3481c1e5..34c9353c9feaa 100644
--- a/lldb/source/Core/DumpDataExtractor.cpp
+++ b/lldb/source/Core/DumpDataExtractor.cpp
@@ -52,7 +52,9 @@ static float half2float(uint16_t half) {
     float f;
     uint32_t u;
   } u;
-  int32_t v = (int16_t)half;
+  // Sign extend to 4 byte.
+  int32_t sign_extended = static_cast<int16_t>(half);
+  uint32_t v = static_cast<uint32_t>(sign_extended);
 
   if (0 == (v & 0x7c00)) {
     u.u = v & 0x80007FFFU;