[lldb] Fix ELF core debugging

[splhack]

DynamicLoader does not use ProcessElfCore NT_FILE entries to get
UUID. Use GetModuleSpec to get UUID from Process.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Kazuki Sakamoto (splhack)

Changes

Addressing two issues on ELF core debugging

1. ProcessElfCore::FindBuidIdInCoreMemory reads wrong address for ELF header (fixed by @clayborg)
2. DynamicLoader does not use ProcessElfCore NT_FILE entries to get UUID. Add FindBuildId to get UUID from Process.

---

Full diff: https://github.com/llvm/llvm-project/pull/117070.diff

5 Files Affected:

• (modified) lldb/include/lldb/Target/Process.h (+2)
• (modified) lldb/source/Core/DynamicLoader.cpp (+4)
• (modified) lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp (+9-1)
• (modified) lldb/source/Plugins/Process/elf-core/ProcessElfCore.h (+3)
• (modified) lldb/source/Target/Process.cpp (+5)

diff --git a/lldb/include/lldb/Target/Process.h b/lldb/include/lldb/Target/Process.h
index b8c53a474ba6b9..2f0cf78f260c5a 100644
--- a/lldb/include/lldb/Target/Process.h
+++ b/lldb/include/lldb/Target/Process.h
@@ -1380,6 +1380,8 @@ class Process : public std::enable_shared_from_this<Process>,
 
   virtual bool GetProcessInfo(ProcessInstanceInfo &info);
 
+  virtual lldb_private::UUID FindBuildId(const llvm::StringRef path);
+
   /// Get the exit status for a process.
   ///
   /// \return
diff --git a/lldb/source/Core/DynamicLoader.cpp b/lldb/source/Core/DynamicLoader.cpp
index 68d6ab0850853f..cc396e92721123 100644
--- a/lldb/source/Core/DynamicLoader.cpp
+++ b/lldb/source/Core/DynamicLoader.cpp
@@ -157,6 +157,10 @@ DynamicLoader::GetSectionListFromModule(const ModuleSP module) const {
 ModuleSP DynamicLoader::FindModuleViaTarget(const FileSpec &file) {
   Target &target = m_process->GetTarget();
   ModuleSpec module_spec(file, target.GetArchitecture());
+  if (UUID uuid = m_process->FindBuildId(file.GetPath())) {
+    // Process may have the UUID for the module, e.g. ELF core.
+    module_spec.GetUUID().SetFromStringRef(uuid.GetAsString());
+  }
 
   if (ModuleSP module_sp = target.GetImages().FindFirstModule(module_spec))
     return module_sp;
diff --git a/lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp b/lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp
index 7955594bf5d94c..8ad6b83d77effe 100644
--- a/lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp
+++ b/lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp
@@ -281,6 +281,13 @@ void ProcessElfCore::UpdateBuildIdForNTFileEntries() {
   }
 }
 
+UUID ProcessElfCore::FindBuildId(const llvm::StringRef path) {
+  for (NT_FILE_Entry &entry : m_nt_file_entries)
+    if (path == entry.path)
+      return entry.uuid;
+  return UUID();
+}
+
 lldb_private::DynamicLoader *ProcessElfCore::GetDynamicLoader() {
   if (m_dyld_up.get() == nullptr)
     m_dyld_up.reset(DynamicLoader::FindPlugin(
@@ -1034,7 +1041,8 @@ UUID ProcessElfCore::FindBuidIdInCoreMemory(lldb::addr_t address) {
     std::vector<uint8_t> note_bytes;
     note_bytes.resize(program_header.p_memsz);
 
-    byte_read = ReadMemory(program_header.p_vaddr, note_bytes.data(),
+    const lldb::addr_t program_header_vaddr = program_header.p_vaddr + address;
+    byte_read = ReadMemory(program_header_vaddr, note_bytes.data(),
                            program_header.p_memsz, error);
     if (byte_read != program_header.p_memsz)
       continue;
diff --git a/lldb/source/Plugins/Process/elf-core/ProcessElfCore.h b/lldb/source/Plugins/Process/elf-core/ProcessElfCore.h
index 280c61ed376396..303f18249a976e 100644
--- a/lldb/source/Plugins/Process/elf-core/ProcessElfCore.h
+++ b/lldb/source/Plugins/Process/elf-core/ProcessElfCore.h
@@ -97,6 +97,9 @@ class ProcessElfCore : public lldb_private::PostMortemProcess {
 
   bool GetProcessInfo(lldb_private::ProcessInstanceInfo &info) override;
 
+  // Returns the gnu uuid from matched NT_FILE entry
+  lldb_private::UUID FindBuildId(const llvm::StringRef path) override;
+
 protected:
   void Clear();
 
diff --git a/lldb/source/Target/Process.cpp b/lldb/source/Target/Process.cpp
index 9125ceca74a003..d2921f623bbefc 100644
--- a/lldb/source/Target/Process.cpp
+++ b/lldb/source/Target/Process.cpp
@@ -6080,6 +6080,11 @@ bool Process::GetProcessInfo(ProcessInstanceInfo &info) {
   return platform_sp->GetProcessInfo(GetID(), info);
 }
 
+lldb_private::UUID Process::FindBuildId(const llvm::StringRef path) {
+  lldb_private::UUID invalid_uuid;
+  return invalid_uuid;
+}
+
 ThreadCollectionSP Process::GetHistoryThreads(lldb::addr_t addr) {
   ThreadCollectionSP threads;
 

[cs01]

Thank you! Are there any unit tests that can exercise this?

Or at least repro steps to generate a core with the elf headers in case any one wants to manually test.

[clayborg]

The reading of build IDs is tracked in this PR: #117028

[splhack]

The reading of build IDs is tracked in this PR: #117028

will rebase onto #117028

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[clayborg]

Change to:

module_spec.GetUUID() = entry.uuid;

[splhack]

updated

[vvereschaka]

Hi @splhack ,

looks like these changes break lldb-api::TestLoadUnload.py test on the LLDB remote-linux builders:

• https://lab.llvm.org/buildbot/#/builders/195/builds/1435
• https://lab.llvm.org/staging/#/builders/197/builds/663

[splhack]

@vvereschaka let me check

[splhack]

@clayborg most likely calling GetModuleSpec is the cause of these failures.
ProcessGDBRemote fetches modules from remote.
FindBuildId does not have the issue. What do you think?

looks like these changes break lldb-api::TestLoadUnload.py test on the LLDB remote-linux builders:

• https://lab.llvm.org/buildbot/#/builders/195/builds/1435
• https://lab.llvm.org/staging/#/builders/197/builds/663