[Lldb-commits] [PATCH] D134842: Improve dynamic loader support in DynamicLoaderPOSIXDYLD when using core files.

[Greg Clayton via Phabricator via lldb-commits]

clayborg created this revision.
clayborg added reviewers: labath, JDevlieghere, yinghuitan.
Herald added a project: All.
clayborg requested review of this revision.
Herald added a project: LLDB.
Herald added a subscriber: lldb-commits.

Prior to this fix, no shared libraries would be loaded for a core file, even if they exist on the current machine. The issue was the DYLDRendezvous would read a DYLDRendezvous::Rendezvous from memory of the process in DYLDRendezvous::Resolve() which would read some ld.so structures as they existed in the middle of a process' lifetime. In core files we see, the DYLDRendezvous::Rendezvous::state would be set to eAdd for running processes. When ProcessELFCore.cpp would load the core file, it would call DynamicLoaderPOSIXDYLD::DidAttach(), which would call the above Rendezvous functions. The issue came when during the DidAttach function it call DYLDRendezvous::GetAction() which would return eNoAction if the DYLDRendezvous::m_current.state was read from memory as eAdd. This caused no shared libraries to be loaded for any ELF core files. We now detect if we have a core file and after reading the DYLDRendezvous::m_current.state from memory we set it to eConsistent, which causes DYLDRendezvous::GetAction() to return the correct action of eTakeSnapshot and shared libraries get loaded.

We also improve the DynamicLoaderPOSIXDYLD class to not try and set any breakpoints to catch shared library loads/unloads when we have a core file, which saves a bit of time.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D134842

Files:
  lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.cpp
  lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.h
  lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp
  lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.h


Index: lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.h
===================================================================
--- lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.h
+++ lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.h
@@ -91,6 +91,9 @@
   std::map<lldb::ModuleWP, lldb::addr_t, std::owner_less<lldb::ModuleWP>>
       m_loaded_modules;
 
+  /// Returns true if the process is for a core file.
+  bool IsCoreFile() const;
+
   /// If possible sets a breakpoint on a function called by the runtime
   /// linker each time a module is loaded or unloaded.
   bool SetRendezvousBreakpoint();
Index: lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp
===================================================================
--- lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp
+++ lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp
@@ -213,6 +213,10 @@
 void DynamicLoaderPOSIXDYLD::ProbeEntry() {
   Log *log = GetLog(LLDBLog::DynamicLoader);
 
+  // If we have a core file, we don't need any breakpoints.
+  if (IsCoreFile())
+    return;
+
   const addr_t entry = GetEntryPoint();
   if (entry == LLDB_INVALID_ADDRESS) {
     LLDB_LOGF(
@@ -297,6 +301,11 @@
 
 bool DynamicLoaderPOSIXDYLD::SetRendezvousBreakpoint() {
   Log *log = GetLog(LLDBLog::DynamicLoader);
+
+  // If we have a core file, we don't need any breakpoints.
+  if (IsCoreFile())
+    return false;
+
   if (m_dyld_bid != LLDB_INVALID_BREAK_ID) {
     LLDB_LOG(log,
              "Rendezvous breakpoint breakpoint id {0} for pid {1}"
@@ -829,3 +838,7 @@
 
   return module_sp->GetFileSpec().GetPath() == "[vdso]";
 }
+
+bool DynamicLoaderPOSIXDYLD::IsCoreFile() const {
+  return !m_process->IsLiveDebugSession();
+}
Index: lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.h
===================================================================
--- lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.h
+++ lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.h
@@ -267,6 +267,8 @@
 
   bool FindMetadata(const char *name, PThreadField field, uint32_t &value);
 
+  bool IsCoreFile() const;
+
   enum RendezvousAction {
     eNoAction,
     eTakeSnapshot,
Index: lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.cpp
===================================================================
--- lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.cpp
+++ lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.cpp
@@ -171,6 +171,15 @@
   if (!(cursor = ReadPointer(cursor + padding, &info.ldbase)))
     return false;
 
+  // If we have a core file, we will read the current rendezvous state
+  // from the core file's memory which will indicate there is nothing
+  // to do, but we need it to load all of the shared libraries. If we
+  // don't change this, then "info.state" will be set to eAdd and the
+  // m_previous.state will be eConsistent and GetAction() will return
+  // eNoAction when we need it to return eTakeSnapshot.
+  if (IsCoreFile())
+    info.state = eConsistent;
+
   // The rendezvous was successfully read.  Update our internal state.
   m_rendezvous_addr = info_addr;
   m_previous = m_current;
@@ -664,3 +673,7 @@
     LLDB_LOGF(log, "      Prev : %" PRIx64, I->prev);
   }
 }
+
+bool DYLDRendezvous::IsCoreFile() const {
+  return !m_process->IsLiveDebugSession();
+}


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