[Lldb-commits] [PATCH] D16772: Fix single stepping over the IT instruction

[Tamas Berghammer via lldb-commits]

tberghammer created this revision.
tberghammer added reviewers: omjavaid, clayborg.
tberghammer added a subscriber: lldb-commits.
Herald added a subscriber: aemerson.

Fix single stepping over the IT instruction

The ARM instruction emulator had 2 bugs related to the handling of the
IT instruction causing an error in single stepping:
* We haven't initialized the IT mask from the CPSR so if the last
  instruction of the IT block is a branch and the condition is false
  then the emulator evaluated the branch what resulted in an incorrect
  pc for the next instruction.
* The ITSTATE was advanced before the execution of each instruction. As
  a result the emulator was using the condition of following instruction
  in every case. The ITSTATE should be edvanced after the execution of
  an instruction except after an IT instruction.

http://reviews.llvm.org/D16772

Files:
  source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp

Index: source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp
===================================================================
--- source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp
+++ source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp
@@ -13062,6 +13062,15 @@
                 m_opcode_mode = eModeARM;
                 m_opcode.SetOpcode32 (MemARead(read_inst_context, pc, 4, 0, &success), GetByteOrder());
             }
+
+            if (!m_ignore_conditions)
+            {
+                // If we are not ignoreing the conditions then init the it session from the current
+                // value of cpsr.
+                uint32_t it = (Bits32(m_opcode_cpsr, 15, 10) << 2) | Bits32(m_opcode_cpsr, 26, 25);
+                if (it != 0)
+                    m_it_session.InitIT(it);
+            }
         }
     }
     if (!success)
@@ -13572,10 +13581,6 @@
 bool
 EmulateInstructionARM::EvaluateInstruction (uint32_t evaluate_options)
 {
-    // Advance the ITSTATE bits to their values for the next instruction.
-    if (m_opcode_mode == eModeThumb && m_it_session.InITBlock())
-        m_it_session.ITAdvance();
-
     ARMOpcode *opcode_data = NULL;
    
     if (m_opcode_mode == eModeThumb)
@@ -13614,7 +13619,13 @@
     success = (this->*opcode_data->callback) (m_opcode.GetOpcode32(), opcode_data->encoding);  
     if (!success)
         return false;
-        
+
+    // Advance the ITSTATE bits to their values for the next instruction if we haven't just executed
+    // an IT instruction what initialized it.
+    if (m_opcode_mode == eModeThumb && m_it_session.InITBlock() &&
+        opcode_data->callback != &EmulateInstructionARM::EmulateIT)
+        m_it_session.ITAdvance();
+
     if (auto_advance_pc)
     {
         uint32_t after_pc_value = ReadRegisterUnsigned (eRegisterKindDWARF, dwarf_pc, 0, &success);


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