[Lldb-commits] [PATCH] D143232: Return an error when the CFA resolves to no known register, instead of segfaulting

[Jason Molenda via Phabricator via lldb-commits]

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I'm working on a bug report where lldb crashes while trying to read the register that is used to calculate the canonical frame address for the first frame in a stack trace.  I haven't figured out how they're getting in this state yet, but I want to add a check for a failure to find a register in this case, and declare the stack frame as invalid to handle the error.  I also added an assert so we can catch it early in debug builds if it ever comes up here.

I think returning no valid stack frame for this thread is going to be a better failure mode than having the debugger crash out from under them, ending the debug session.  It's still a pretty bad failure, but hopefully we can collect some logging with this if it comes up again.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D143232

Files:
  lldb/source/Target/RegisterContextUnwind.cpp


Index: lldb/source/Target/RegisterContextUnwind.cpp
===================================================================
--- lldb/source/Target/RegisterContextUnwind.cpp
+++ lldb/source/Target/RegisterContextUnwind.cpp
@@ -37,6 +37,8 @@
 #include "lldb/Utility/RegisterValue.h"
 #include "lldb/Utility/VASPrintf.h"
 #include "lldb/lldb-private.h"
+
+#include <cassert>
 #include <memory>
 
 using namespace lldb;
@@ -289,6 +291,13 @@
   } else
     ReadFrameAddress(row_register_kind, active_row->GetAFAValue(), m_afa);
 
+  if (m_cfa == LLDB_INVALID_ADDRESS && m_afa == LLDB_INVALID_ADDRESS) {
+    UnwindLogMsg(
+        "could not read CFA or AFA values for first frame, not valid.");
+    m_frame_type = eNotAValidFrame;
+    return;
+  }
+
   UnwindLogMsg("initialized frame current pc is 0x%" PRIx64 " cfa is 0x%" PRIx64
                " afa is 0x%" PRIx64 " using %s UnwindPlan",
                (uint64_t)m_current_pc.GetLoadAddress(exe_ctx.GetTargetPtr()),
@@ -2116,6 +2125,14 @@
   }
 
   const RegisterInfo *reg_info = GetRegisterInfoAtIndex(lldb_regnum);
+  assert(reg_info);
+  if (!reg_info) {
+    UnwindLogMsg(
+        "Could not find RegisterInfo definition for lldb register number %d",
+        lldb_regnum);
+    return false;
+  }
+
   RegisterValue reg_value;
   // if this is frame 0 (currently executing frame), get the requested reg
   // contents from the actual thread registers


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