Recognize BSS-only DATA segments as sections that need to be slid/loaded at addresses

[jasonmolenda]

Summary

ObjectFileMachO::SetLoadAddress() takes a slide or base load address and applies the correct address difference to each section in the Target. It only makes these changes to "loadable" sections and one of the heuristics incorrectly disqualified a DATA segment that has no on-disk content, e.g. a BSS-only DATA segment. A DATA segment is allowed to have no file size; this is a small patch to SectionIsLoadable to recognize that. And add a quick test case.

[JDevlieghere]

LGTM

lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp

Section *ObjectFileMachO::GetMachHeaderSection() {
 
   return nullptr;
 }
 
 bool ObjectFileMachO::SectionIsLoadable(const Section *section) {
   if (!section)
     return false;
   const bool is_dsym = (m_header.filetype == MH_DSYM);
-  if (section->GetFileSize() == 0 && !is_dsym)
+  if (section->GetFileSize() == 0 && !is_dsym &&
+      section->GetName() != GetSegmentNameDATA())
     return false;
   if (section->IsThreadSpecific())
     return false;
   if (GetModule().get() != section->GetModule().get())
     return false;
   // Be careful with __LINKEDIT and __DWARF segments
   if (section->GetName() == GetSegmentNameLINKEDIT() ||
       section->GetName() == GetSegmentNameDWARF()) {

lldb/test/API/macosx/bss-only-data-section-sliding/Makefile

+C_SOURCES := main.c
+
+include Makefile.rules

lldb/test/API/macosx/bss-only-data-section-sliding/TestBSSOnlyDataSectionSliding.py

+"""Test that we a BSS-data only DATA segment is slid with other segments."""
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestBSSOnlyDataSectionSliding(TestBase):
+    @skipUnlessDarwin
+    def test_with_python_api(self):
+        """Test that we get thread names when interrupting a process."""
+        self.build()
+        exe = self.getBuildArtifact("a.out")
+
+        target = self.dbg.CreateTarget(exe, "", "", False, lldb.SBError())
+        self.assertTrue(target, VALID_TARGET)
+
+        module = target.modules[0]
+        self.assertTrue(module.IsValid())
+        data_sect = module.section["__DATA"]
+        self.assertTrue(data_sect.IsValid())
+
+        target.SetModuleLoadAddress(module, 0x170000000)
+        self.assertEqual(
+            data_sect.GetFileAddress() + 0x170000000, data_sect.GetLoadAddress(target)
+        )

lldb/test/API/macosx/bss-only-data-section-sliding/main.c

+int glob = 0;
+int main() { return glob; }