[LLDB] Fix debuginfo ELF files overwriting Unified Section List (#166635)

Recently I've been deep diving ELF cores in LLDB, aspiring to move LLDB
closer to GDB in capability. One issue I encountered was a system lib
losing it's unwind plan when loading the debuginfo. The reason for this
was the debuginfo has the eh_frame section stripped and the main
executable did not.

The root cause of this was this line in
[ObjectFileElf](https://github.com/llvm/llvm-project/blob/163933e9e7099f352ff8df1973f9a9c3d7def6c5/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp#L1972)
```
  // For eTypeDebugInfo files, the Symbol Vendor will take care of updating the
  // unified section list.
  if (GetType() != eTypeDebugInfo)
    unified_section_list = *m_sections_up;
```

This would always be executed because CalculateType can never return an
eTypeDebugInfo
```
ObjectFile::Type ObjectFileELF::CalculateType() {
  switch (m_header.e_type) {
  case llvm::ELF::ET_NONE:
    // 0 - No file type
    return eTypeUnknown;

  case llvm::ELF::ET_REL:
    // 1 - Relocatable file
    return eTypeObjectFile;

  case llvm::ELF::ET_EXEC:
    // 2 - Executable file
    return eTypeExecutable;

  case llvm::ELF::ET_DYN:
    // 3 - Shared object file
    return eTypeSharedLibrary;

  case ET_CORE:
    // 4 - Core file
    return eTypeCoreFile;

  default:
    break;
  }
  return eTypeUnknown;
}
```

This makes sense as there isn't a explicit sh_type to denote that this
file is a debuginfo. After some discussion with @clayborg and
@GeorgeHuyubo we settled on joining the exciting unified section list
with whatever new sections were being added. Adding each new unique
section, or taking the section with the maximum file size. We picked
this strategy to pick the section with the most information. In most
scenarios, LHS should be SHT_NOBITS and RHS would be SHT_PROGBITS.

Here is a diagram documenting the existing vs proposed new way.
<img width="1666" height="1093" alt="image"
src="https://github.com/user-attachments/assets/73ba9620-c737-439e-9934-ac350d88a3b5"
/>

7 files changed, 475 insertions, 0 deletions

diff --git a/lldb/test/API/python_api/unified_section_list/Makefile b/lldb/test/API/python_api/unified_section_list/Makefile
new file mode 100644
index 0000000..431e716
--- /dev/null
+++ b/lldb/test/API/python_api/unified_section_list/Makefile
@@ -0,0 +1,5 @@
+CXX_SOURCES := main.cpp
+
+SPLIT_DEBUG_SYMBOLS := YES
+
+include Makefile.rules
diff --git a/lldb/test/API/python_api/unified_section_list/TestModuleUnifiedSectionList.py b/lldb/test/API/python_api/unified_section_list/TestModuleUnifiedSectionList.py
new file mode 100644
index 0000000..93b23d0
--- /dev/null
+++ b/lldb/test/API/python_api/unified_section_list/TestModuleUnifiedSectionList.py
@@ -0,0 +1,285 @@
+"""
+Test Unified Section List merging.
+"""
+
+import os
+import shutil
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+from lldbsuite.test.lldbutil import symbol_type_to_str
+
+
+class ModuleUnifiedSectionList(TestBase):
+    @skipUnlessPlatform(["linux", "freebsd", "netbsd"])
+    def test_unified_section_list(self):
+        self.build()
+        exe = self.getBuildArtifact("a.out")
+        debug_info = self.getBuildArtifact("a.out.debug")
+        new_dir = os.path.join(os.path.dirname(debug_info), "new_dir")
+        os.mkdir(new_dir)
+        renamed_debug_info = os.path.join(new_dir, "renamed.debug")
+        os.rename(debug_info, renamed_debug_info)
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+        self.assertGreater(target.GetNumModules(), 0)
+
+        main_exe_module = target.GetModuleAtIndex(0)
+        eh_frame = main_exe_module.FindSection(".eh_frame")
+        self.assertTrue(eh_frame.IsValid())
+        self.assertGreater(eh_frame.size, 0)
+
+        # Should be stripped in main executable.
+        debug_info_section = main_exe_module.FindSection(".debug_info")
+        self.assertFalse(debug_info_section.IsValid())
+
+        ci = self.dbg.GetCommandInterpreter()
+        res = lldb.SBCommandReturnObject()
+        ci.HandleCommand(f"target symbols add {renamed_debug_info}", res)
+        self.assertTrue(res.Succeeded())
+
+        # Should be stripped in .debuginfo but be present in main executable.
+        main_exe_module = target.GetModuleAtIndex(0)
+        eh_frame = main_exe_module.FindSection(".eh_frame")
+        self.assertTrue(eh_frame.IsValid())
+        self.assertGreater(eh_frame.size, 0)
+
+        # Should be unified and both sections should have contents.
+        debug_info_section = main_exe_module.FindSection(".debug_info")
+        self.assertTrue(debug_info_section.IsValid())
+        self.assertGreater(debug_info_section.file_size, 0)
+
+    def test_unified_section_list_overwrite_larger_section(self):
+        """
+        Test the merging of an ELF file with another ELF File where all the new sections are bigger, validating we
+        overwrite .comment from SHT_NOBITS to the new SHT_PROGBITS section and the smaller .text with the larger
+        .text
+        """
+        exe = self.getBuildArtifact("a.out")
+        self.yaml2obj("main.yaml", exe)
+
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+        main_exe_module = target.GetModuleAtIndex(0)
+
+        # First we verify out .text section is the expected BEC0FFEE
+        text_before_merge = main_exe_module.FindSection(".text")
+        self.assertTrue(text_before_merge.IsValid())
+        error = lldb.SBError()
+        section_content = text_before_merge.data.ReadRawData(
+            error, 0, text_before_merge.data.size
+        )
+        self.assertTrue(error.Success())
+        self.assertEqual(section_content, bytes.fromhex("BEC0FFEE"))
+
+        # .comment in main.yaml should be SHT_NOBITS, and size 0
+        comment_before_merge = main_exe_module.FindSection(".comment")
+        self.assertTrue(comment_before_merge.IsValid())
+        self.assertEqual(comment_before_merge.data.size, 0)
+
+        # yamlize the main.largertext.yaml and force symbol loading
+        debug_info = self.getBuildArtifact("a.out.debug")
+        self.yaml2obj("main.largertext.yaml", debug_info)
+
+        ci = self.dbg.GetCommandInterpreter()
+        res = lldb.SBCommandReturnObject()
+        ci.HandleCommand(f"target symbols add {debug_info}", res)
+        self.assertTrue(res.Succeeded())
+
+        # verify we took the larger .text section
+        main_exe_module_after_merge = target.GetModuleAtIndex(0)
+        text_after_merge = main_exe_module_after_merge.FindSection(".text")
+        self.assertTrue(text_after_merge.IsValid())
+        self.assertGreater(text_after_merge.data.size, text_before_merge.data.size)
+        section_content_after_merge = text_after_merge.data.ReadRawData(
+            error, 0, text_after_merge.data.size
+        )
+        self.assertTrue(error.Success())
+        self.assertEqual(section_content_after_merge, bytes.fromhex("BEC0FFEEEEFF0CEB"))
+
+        # in main.largertext.yaml comment is not SHT_NOBITS, and so we should see
+        # the size > 0 and equal to BAADF00D
+        comment_after_merge = main_exe_module_after_merge.FindSection(".comment")
+        self.assertTrue(comment_after_merge.IsValid())
+        comment_content_after_merge = comment_after_merge.data.ReadRawData(
+            error, 0, comment_after_merge.data.size
+        )
+
+        self.assertTrue(error.Success())
+        self.assertEqual(comment_content_after_merge, bytes.fromhex("BAADF00D"))
+
+    def test_unified_section_list_overwrite_smaller_section(self):
+        """
+        Test the merging of an ELF file with another ELF File where all the existing sections are bigger, validating we don't
+        overwrite with the SHT_NOBITS for .comment or the smaller .text section.
+        """
+        exe = self.getBuildArtifact("a.out")
+        self.yaml2obj("main.largertext.yaml", exe)
+
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+        main_exe_module = target.GetModuleAtIndex(0)
+
+        # Same as above test but inverse, verify our larger .text section
+        # is the expected BEC0FFEE palindrome
+        text_before_merge = main_exe_module.FindSection(".text")
+        self.assertTrue(text_before_merge.IsValid())
+        error = lldb.SBError()
+        section_content = text_before_merge.data.ReadRawData(
+            error, 0, text_before_merge.data.size
+        )
+        self.assertTrue(error.Success())
+        self.assertEqual(section_content, bytes.fromhex("BEC0FFEEEEFF0CEB"))
+
+        # Comment is SHT_PROGBITS on the larger yaml and should remain
+        # the same after merge.
+        comment_before_merge = main_exe_module.FindSection(".comment")
+        self.assertTrue(comment_before_merge.IsValid())
+        comment_content = comment_before_merge.data.ReadRawData(
+            error, 0, comment_before_merge.data.size
+        )
+
+        self.assertTrue(error.Success())
+        self.assertEqual(comment_content, bytes.fromhex("BAADF00D"))
+
+        debug_info = self.getBuildArtifact("a.out.debug")
+        self.yaml2obj("main.yaml", debug_info)
+
+        ci = self.dbg.GetCommandInterpreter()
+        res = lldb.SBCommandReturnObject()
+        ci.HandleCommand(f"target symbols add {debug_info}", res)
+        self.assertTrue(res.Succeeded())
+
+        # Verify we didn't replace the sections after merge.s
+        main_exe_module_after_merge = target.GetModuleAtIndex(0)
+        text_after_merge = main_exe_module_after_merge.FindSection(".text")
+        self.assertTrue(text_after_merge.IsValid())
+        self.assertEqual(text_after_merge.data.size, text_before_merge.data.size)
+        section_content_after_merge = text_after_merge.data.ReadRawData(
+            error, 0, text_after_merge.data.size
+        )
+        self.assertTrue(error.Success())
+        self.assertEqual(section_content_after_merge, bytes.fromhex("BEC0FFEEEEFF0CEB"))
+
+        comment_after_merge = main_exe_module_after_merge.FindSection(".comment")
+        self.assertTrue(comment_after_merge.IsValid())
+        comment_content_after_merge = comment_after_merge.data.ReadRawData(
+            error, 0, comment_after_merge.data.size
+        )
+
+        self.assertTrue(error.Success())
+        self.assertEqual(comment_content_after_merge, bytes.fromhex("BAADF00D"))
+
+    def test_unified_section_list_overwrite_mixed_merge(self):
+        """
+        Test the merging of an ELF file with another ELF File where the lhs has a larger .comment section
+        and the RHS has a larger .text section.
+        """
+        exe = self.getBuildArtifact("a.out")
+        self.yaml2obj("main.largercomment.yaml", exe)
+
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+        main_exe_module = target.GetModuleAtIndex(0)
+
+        # Verify we have the expected smaller BEC0FFEE
+        text_before_merge = main_exe_module.FindSection(".text")
+        self.assertTrue(text_before_merge.IsValid())
+        error = lldb.SBError()
+        section_content = text_before_merge.data.ReadRawData(
+            error, 0, text_before_merge.data.size
+        )
+        self.assertTrue(error.Success())
+        self.assertEqual(section_content, bytes.fromhex("BEC0FFEE"))
+
+        # Verify we have the larger palindromic comment
+        comment_before_merge = main_exe_module.FindSection(".comment")
+        self.assertTrue(comment_before_merge.IsValid())
+        comment_content = comment_before_merge.data.ReadRawData(
+            error, 0, comment_before_merge.data.size
+        )
+
+        self.assertTrue(error.Success())
+        self.assertEqual(comment_content, bytes.fromhex("BAADF00DF00DBAAD"))
+
+        debug_info = self.getBuildArtifact("a.out.debug")
+        self.yaml2obj("main.largertext.yaml", debug_info)
+
+        ci = self.dbg.GetCommandInterpreter()
+        res = lldb.SBCommandReturnObject()
+        ci.HandleCommand(f"target symbols add {debug_info}", res)
+        self.assertTrue(res.Succeeded())
+
+        # Verify we replaced .text
+        main_exe_module_after_merge = target.GetModuleAtIndex(0)
+        text_after_merge = main_exe_module_after_merge.FindSection(".text")
+        self.assertTrue(text_after_merge.IsValid())
+        section_content_after_merge = text_after_merge.data.ReadRawData(
+            error, 0, text_after_merge.data.size
+        )
+        self.assertTrue(error.Success())
+        self.assertEqual(section_content_after_merge, bytes.fromhex("BEC0FFEEEEFF0CEB"))
+
+        # Verify .comment is still the same.
+        comment_after_merge = main_exe_module_after_merge.FindSection(".comment")
+        self.assertTrue(comment_after_merge.IsValid())
+        comment_content_after_merge = comment_after_merge.data.ReadRawData(
+            error, 0, comment_after_merge.data.size
+        )
+
+        self.assertTrue(error.Success())
+        self.assertEqual(comment_content_after_merge, bytes.fromhex("BAADF00DF00DBAAD"))
+
+    def test_unified_section_list_overwrite_equal_size(self):
+        """
+        Test the merging of an ELF file with an ELF file with sections of the same size with different values
+        .text
+        """
+        exe = self.getBuildArtifact("a.out")
+        self.yaml2obj("main.yaml", exe)
+
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+        main_exe_module = target.GetModuleAtIndex(0)
+
+        # First we verify out .text section is the expected BEC0FFEE
+        text_before_merge = main_exe_module.FindSection(".text")
+        self.assertTrue(text_before_merge.IsValid())
+        error = lldb.SBError()
+        section_content = text_before_merge.data.ReadRawData(
+            error, 0, text_before_merge.data.size
+        )
+        self.assertTrue(error.Success())
+        self.assertEqual(section_content, bytes.fromhex("BEC0FFEE"))
+
+        # .comment in main.yaml should be SHT_NOBITS, and size 0
+        comment_before_merge = main_exe_module.FindSection(".comment")
+        self.assertTrue(comment_before_merge.IsValid())
+        self.assertEqual(comment_before_merge.data.size, 0)
+
+        # yamlize the main with the .text reversed from BEC0FFEE
+        # to EEFF0CEB. We should still keep our .text with BEC0FFEE
+        debug_info = self.getBuildArtifact("a.out.debug")
+        self.yaml2obj("main.reversedtext.yaml", debug_info)
+
+        ci = self.dbg.GetCommandInterpreter()
+        res = lldb.SBCommandReturnObject()
+        ci.HandleCommand(f"target symbols add {debug_info}", res)
+        self.assertTrue(res.Succeeded())
+
+        # verify .text did not change
+        main_exe_module_after_merge = target.GetModuleAtIndex(0)
+        text_after_merge = main_exe_module_after_merge.FindSection(".text")
+        self.assertTrue(text_after_merge.IsValid())
+        section_content_after_merge = text_after_merge.data.ReadRawData(
+            error, 0, text_after_merge.data.size
+        )
+        self.assertTrue(error.Success())
+        self.assertEqual(section_content_after_merge, bytes.fromhex("BEC0FFEE"))
+
+        # verify comment did not change
+        comment_afer_merge = main_exe_module_after_merge.FindSection(".comment")
+        self.assertTrue(comment_afer_merge.IsValid())
+        self.assertEqual(comment_afer_merge.data.size, 0)
diff --git a/lldb/test/API/python_api/unified_section_list/main.cpp b/lldb/test/API/python_api/unified_section_list/main.cpp
new file mode 100644
index 0000000..45fd52e
--- /dev/null
+++ b/lldb/test/API/python_api/unified_section_list/main.cpp
@@ -0,0 +1,3 @@
+#include <stdio.h>
+
+int main() { printf("Hello World\n"); }
diff --git a/lldb/test/API/python_api/unified_section_list/main.largercomment.yaml b/lldb/test/API/python_api/unified_section_list/main.largercomment.yaml
new file mode 100644
index 0000000..f786006
--- /dev/null
+++ b/lldb/test/API/python_api/unified_section_list/main.largercomment.yaml
@@ -0,0 +1,46 @@
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+  Entry:           0x1040
+ProgramHeaders:
+  - Type:            PT_PHDR
+    Flags:           [ PF_R ]
+    VAddr:           0x40
+    Align:           0x8
+    Offset:          0x40
+  - Type:            PT_LOAD
+    Flags:           [ PF_R ]
+    FirstSec:        .text
+    LastSec:         .fini
+    Align:           0x1000
+    Offset:          0x0
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x1040
+    AddressAlign:    0x10
+    Content:         BEC0FFEE
+  - Name:            .fini
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x1140
+    AddressAlign:    0x4
+    Content:         DEADBEEF
+  - Name:            .comment
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x3140
+    AddressAlign:    0x4
+    Content:         BAADF00DF00DBAAD
+Symbols:
+  - Name:            main
+    Type:            STT_FUNC
+    Section:         .text
+    Binding:         STB_GLOBAL
+    Value:           0x1130
+    Size:            0xF
+...
diff --git a/lldb/test/API/python_api/unified_section_list/main.largertext.yaml b/lldb/test/API/python_api/unified_section_list/main.largertext.yaml
new file mode 100644
index 0000000..6450e67
--- /dev/null
+++ b/lldb/test/API/python_api/unified_section_list/main.largertext.yaml
@@ -0,0 +1,46 @@
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+  Entry:           0x1040
+ProgramHeaders:
+  - Type:            PT_PHDR
+    Flags:           [ PF_R ]
+    VAddr:           0x40
+    Align:           0x8
+    Offset:          0x40
+  - Type:            PT_LOAD
+    Flags:           [ PF_R ]
+    FirstSec:        .text
+    LastSec:         .fini
+    Align:           0x1000
+    Offset:          0x0
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x1040
+    AddressAlign:    0x10
+    Content:         BEC0FFEEEEFF0CEB
+  - Name:            .fini
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x1140
+    AddressAlign:    0x4
+    Content:         DEADBEEF
+  - Name:            .comment
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x3140
+    AddressAlign:    0x4
+    Content:         BAADF00D
+Symbols:
+  - Name:            main
+    Type:            STT_FUNC
+    Section:         .text
+    Binding:         STB_GLOBAL
+    Value:           0x1130
+    Size:            0xF
+...
diff --git a/lldb/test/API/python_api/unified_section_list/main.reversedtext.yaml b/lldb/test/API/python_api/unified_section_list/main.reversedtext.yaml
new file mode 100644
index 0000000..5720666
--- /dev/null
+++ b/lldb/test/API/python_api/unified_section_list/main.reversedtext.yaml
@@ -0,0 +1,45 @@
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+  Entry:           0x1040
+ProgramHeaders:
+  - Type:            PT_PHDR
+    Flags:           [ PF_R ]
+    VAddr:           0x40
+    Align:           0x8
+    Offset:          0x40
+  - Type:            PT_LOAD
+    Flags:           [ PF_R ]
+    FirstSec:        .text
+    LastSec:         .fini
+    Align:           0x1000
+    Offset:          0x0
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x1040
+    AddressAlign:    0x10
+    Content:         BEC0FFEE
+  - Name:            .fini
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x1140
+    AddressAlign:    0x4
+    Content:         DEADBEEF
+  - Name:            .comment
+    Type:            SHT_NOBITS
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x3140
+    AddressAlign:    0x4
+Symbols:
+  - Name:            main
+    Type:            STT_FUNC
+    Section:         .text
+    Binding:         STB_GLOBAL
+    Value:           0x1130
+    Size:            0xF
+...
diff --git a/lldb/test/API/python_api/unified_section_list/main.yaml b/lldb/test/API/python_api/unified_section_list/main.yaml
new file mode 100644
index 0000000..5720666
--- /dev/null
+++ b/lldb/test/API/python_api/unified_section_list/main.yaml
@@ -0,0 +1,45 @@
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+  Entry:           0x1040
+ProgramHeaders:
+  - Type:            PT_PHDR
+    Flags:           [ PF_R ]
+    VAddr:           0x40
+    Align:           0x8
+    Offset:          0x40
+  - Type:            PT_LOAD
+    Flags:           [ PF_R ]
+    FirstSec:        .text
+    LastSec:         .fini
+    Align:           0x1000
+    Offset:          0x0
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x1040
+    AddressAlign:    0x10
+    Content:         BEC0FFEE
+  - Name:            .fini
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x1140
+    AddressAlign:    0x4
+    Content:         DEADBEEF
+  - Name:            .comment
+    Type:            SHT_NOBITS
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x3140
+    AddressAlign:    0x4
+Symbols:
+  - Name:            main
+    Type:            STT_FUNC
+    Section:         .text
+    Binding:         STB_GLOBAL
+    Value:           0x1130
+    Size:            0xF
+...