[lldb][ElfCore] Improve main executable detection in core files

[GeorgeHuyubo]

This change improves how LLDB's ProcessElfCore plugin identifies the main executable when loading ELF core files. Previously, the code would simply use the first entry in the NT_FILE section, which is not guaranteed to be the main executable, also the first entry might not have a valid UUID.

1. Storing executable name: Extract the executable name from the ELF NT_PRPSINFO note and store it in m_executable_name

2. Preferential matching: When selecting the main executable from NT_FILE entries, prefer entries whose path ends with the stored executable name

3. UUID-based lookup: Call FindModuleUUID() helper function to properly match modules by path and retrieve a valid UUID

[llvmbot]

@llvm/pr-subscribers-clang-format

@llvm/pr-subscribers-lldb

Author: None (GeorgeHuyubo)

Changes

This change improves how LLDB's ProcessElfCore plugin identifies the main executable when loading ELF core files. Previously, the code would simply use the first entry in the NT_FILE section, which is not guaranteed to be the main executable, also the first entry might not have a valid UUID.

1. Storing executable name: Extract the executable name from the ELF NT_PRPSINFO note and store it in m_executable_name

2. Preferential matching: When selecting the main executable from NT_FILE entries, prefer entries whose path ends with the stored executable name

3. UUID-based lookup: Call FindModuleUUID() helper function to properly match modules by path and retrieve a valid UUID

---

Full diff: https://github.com/llvm/llvm-project/pull/157170.diff

2 Files Affected:

• (modified) lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp (+13-3)
• (modified) lldb/source/Plugins/Process/elf-core/ProcessElfCore.h (+3)

diff --git a/lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp b/lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp
index 88eeddf178788..e88daebebfa7e 100644
--- a/lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp
+++ b/lldb/source/Plugins/Process/elf-core/ProcessElfCore.cpp
@@ -257,12 +257,21 @@ Status ProcessElfCore::DoLoadCore() {
   // the main executable using data we found in the core file notes.
   lldb::ModuleSP exe_module_sp = GetTarget().GetExecutableModule();
   if (!exe_module_sp) {
-    // The first entry in the NT_FILE might be our executable
     if (!m_nt_file_entries.empty()) {
+      // The first entry in the NT_FILE might be our executable
+      llvm::StringRef executable_path = m_nt_file_entries[0].path;
+      // Prefer the NT_FILE entry matching m_executable_name as main executable.
+      for (const NT_FILE_Entry &file_entry : m_nt_file_entries)
+        if (llvm::StringRef(file_entry.path)
+                .ends_with("/" + m_executable_name)) {
+          executable_path = file_entry.path;
+          break;
+        }
+
       ModuleSpec exe_module_spec;
       exe_module_spec.GetArchitecture() = arch;
-      exe_module_spec.GetUUID() = m_nt_file_entries[0].uuid;
-      exe_module_spec.GetFileSpec().SetFile(m_nt_file_entries[0].path,
+      exe_module_spec.GetUUID() = FindModuleUUID(executable_path);
+      exe_module_spec.GetFileSpec().SetFile(executable_path,
                                             FileSpec::Style::native);
       if (exe_module_spec.GetFileSpec()) {
         exe_module_sp =
@@ -935,6 +944,7 @@ llvm::Error ProcessElfCore::parseLinuxNotes(llvm::ArrayRef<CoreNote> notes) {
         return status.ToError();
       thread_data.name.assign (prpsinfo.pr_fname, strnlen (prpsinfo.pr_fname, sizeof (prpsinfo.pr_fname)));
       SetID(prpsinfo.pr_pid);
+      m_executable_name = prpsinfo.pr_fname;
       break;
     }
     case ELF::NT_SIGINFO: {
diff --git a/lldb/source/Plugins/Process/elf-core/ProcessElfCore.h b/lldb/source/Plugins/Process/elf-core/ProcessElfCore.h
index a91c04a277f60..601c8c4ed1b92 100644
--- a/lldb/source/Plugins/Process/elf-core/ProcessElfCore.h
+++ b/lldb/source/Plugins/Process/elf-core/ProcessElfCore.h
@@ -152,6 +152,9 @@ class ProcessElfCore : public lldb_private::PostMortemProcess {
   // NT_FILE entries found from the NOTE segment
   std::vector<NT_FILE_Entry> m_nt_file_entries;
 
+  // Executable name found from the ELF PRPSINFO
+  std::string m_executable_name;
+
   // Parse thread(s) data structures(prstatus, prpsinfo) from given NOTE segment
   llvm::Error ParseThreadContextsFromNoteSegment(
       const elf::ELFProgramHeader &segment_header,

[dmpots]

Can we get a test case for this?

[GeorgeHuyubo]

Can we get a test case for this?

@dmpots I think this file historically lack a good way of testing changes due to difficulties in hand craft a ELF core file using YAML. The ELF support yaml2obj doesn't allow content to be supplied for a program header. It expects section headers to contain data and ELF core files don't have section headers. So it would take some modifications to the ELF obj2yaml and yaml2obj to support this. It would be great if we can add this support at some point if anyone has expertise in the yaml layer as it would be easy to create a core file, reduce it using a different tool, and then obj2yaml it for a test.

[dmpots]

Can we get a test case for this?

I think this file historically lack a good way of testing changes due to difficulties in hand craft a ELF core file using YAML.

I see, thanks for the context. Sounds like something we need to fix, but beyond the scope of this PR.

[dmpots]

LGTM