[Lldb-commits] [PATCH] D81810: LLDB step-instruction gets stuck on jump to self

[Sebastian Österlund via Phabricator via lldb-commits]

sirmc created this revision.
sirmc added a reviewer: LLDB.
sirmc added a project: LLDB.
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sirmc edited the summary of this revision.

When executing `thread step-inst `/ `si` on an instruction that returns to the same PC, LLDB currently keeps stepping indefinitely.

I couldn't find the exact semantics for the step-instruction, but  https://lldb.llvm.org/use/map.html suggests the behavior to be equivalent to GDB's `si`. GDB steps exactly one instruction, without the assumption that the program counter has to change.

Reproduce with the following code:

  int main()
  {
    while(1){};
    return 0;
  }

When compiled with `clang -g a.c`, the above example generates an instruction (X86-64 jmpq) that jumps to the address of itself. When reaching the line with the loop, a `si` will never stop/break in this case, since the assumption is that the PC needs to change for the stepping to be finished.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D81810

Files:
  lldb/source/Target/ThreadPlanStepInstruction.cpp


Index: lldb/source/Target/ThreadPlanStepInstruction.cpp
===================================================================
--- lldb/source/Target/ThreadPlanStepInstruction.cpp
+++ lldb/source/Target/ThreadPlanStepInstruction.cpp
@@ -217,19 +217,16 @@
       }
     }
   } else {
-    lldb::addr_t pc_addr = thread.GetRegisterContext()->GetPC(0);
-    if (pc_addr != m_instruction_addr) {
-      if (--m_iteration_count <= 0) {
-        SetPlanComplete();
-        return true;
-      } else {
-        // We are still stepping, reset the start pc, and in case we've stepped
-        // in or out, reset the current stack id.
-        SetUpState();
-        return false;
-      }
-    } else
+    if (--m_iteration_count <= 0) {
+      SetPlanComplete();
+      return true;
+    } else {
+      // We are still stepping, reset the start pc, and in case we've stepped
+      // in or out, reset the current stack id.
+      SetUpState();
       return false;
+    }
+    return false;
   }
 }
 


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