[Lldb-commits] [lldb] r256847 - Fix for undefined behavior while updating PC value on arm-linux

[Omair Javaid via lldb-commits]

Author: omjavaid
Date: Tue Jan  5 10:56:13 2016
New Revision: 256847

URL: http://llvm.org/viewvc/llvm-project?rev=256847&view=rev
Log:
Fix for undefined behavior while updating PC value on arm-linux

Differential revision: http://reviews.llvm.org/D15877


Modified:
    lldb/trunk/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm.cpp

Modified: lldb/trunk/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm.cpp
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm.cpp?rev=256847&r1=256846&r2=256847&view=diff
==============================================================================
--- lldb/trunk/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm.cpp (original)
+++ lldb/trunk/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm.cpp Tue Jan  5 10:56:13 2016
@@ -973,7 +973,24 @@ NativeRegisterContextLinux_arm::DoWriteR
     if (error.Fail())
         return error;
 
-    m_gpr_arm[offset / sizeof(uint32_t)] = value.GetAsUInt32();
+    uint32_t reg_value = value.GetAsUInt32();
+    // As precaution for an undefined behavior encountered while setting PC we
+    // will clear thumb bit of new PC if we are already in thumb mode; that is
+    // CPSR thumb mode bit is set.
+    if (offset / sizeof(uint32_t) == gpr_pc_arm)
+    {
+        // Check if we are already in thumb mode and
+        // thumb bit of current PC is read out to be zero and
+        // thumb bit of next PC is read out to be one.
+        if ((m_gpr_arm[gpr_cpsr_arm] &  0x20) &&
+            !(m_gpr_arm[gpr_pc_arm] &  0x01) &&
+            (value.GetAsUInt32() & 0x01))
+        {
+            reg_value &= (~1ull);
+        }
+    }
+
+    m_gpr_arm[offset / sizeof(uint32_t)] = reg_value;
     return DoWriteGPR(m_gpr_arm, sizeof(m_gpr_arm));
 }