Improve dynamic loader support in DynamicLoaderPOSIXDYLD when using core files.

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.

Differential Revision: https://reviews.llvm.org/D134842

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.cpp

@@ -190,6 +190,14 @@ bool DYLDRendezvous::IsValid() {
 }
 
 DYLDRendezvous::RendezvousAction DYLDRendezvous::GetAction() const {
+  // If we have a core file, we will read the current rendezvous state
+  // from the core file's memory into m_current which can be in an inconsistent
+  // state, so we can't rely on its state to determine what we should do. We
+  // always need it to load all of the shared libraries one time when we attach
+  // to a core file.
+  if (IsCoreFile())
+    return eTakeSnapshot;
+
   switch (m_current.state) {
 
   case eConsistent:
@@ -664,3 +672,7 @@ void DYLDRendezvous::DumpToLog(Log *log) const {
     LLDB_LOGF(log, "      Prev : %" PRIx64, I->prev);
   }
 }
+
+bool DYLDRendezvous::IsCoreFile() const {
+  return !m_process->IsLiveDebugSession();
+}

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.h

@@ -267,6 +267,8 @@ protected:
 
   bool FindMetadata(const char *name, PThreadField field, uint32_t &value);
 
+  bool IsCoreFile() const;
+
   enum RendezvousAction {
     eNoAction,
     eTakeSnapshot,

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp

@@ -213,6 +213,10 @@ void DynamicLoaderPOSIXDYLD::UnloadSections(const ModuleSP module) {
 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::EntryBreakpointHit(
 
 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 @@ bool DynamicLoaderPOSIXDYLD::AlwaysRelyOnEHUnwindInfo(
 
   return module_sp->GetFileSpec().GetPath() == "[vdso]";
 }
+
+bool DynamicLoaderPOSIXDYLD::IsCoreFile() const {
+  return !m_process->IsLiveDebugSession();
+}

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.h

@@ -91,6 +91,9 @@ protected:
   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();