[Lldb-commits] [lldb] [lldb] [ObjectFileMachO] LLVM_COV is not mapped into firmware memory (PR #86359)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Jason Molenda (jasonmolenda)

<details>
<summary>Changes</summary>

It is possible to gather code coverage in a firmware environment, where the __LLVM_COV segment will not be mapped in memory but does exist in the binary, see
https://llvm.org/devmtg/2020-09/slides/PhippsAlan_EmbeddedCodeCoverage_LLVM_Conf_Talk_final.pdf

The __LLVM_COV segment in the binary happens to be at the same address as the __DATA segment, so if lldb treats this segment as loaded, it shadows the __DATA segment and address->symbol resolution can fail.

For these non-userland code cases, we need to mark __LLVM_COV as not a loadable segment.

rdar://124475661

---
Full diff: https://github.com/llvm/llvm-project/pull/86359.diff


2 Files Affected:

- (modified) lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp (+12) 
- (modified) lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.h (+1) 


``````````diff
diff --git a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
index bcf3a3274cf3a0..1caf93659956b4 100644
--- a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
+++ b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
@@ -905,6 +905,11 @@ ConstString ObjectFileMachO::GetSegmentNameDWARF() {
   return g_section_name;
 }
 
+ConstString ObjectFileMachO::GetSegmentNameLLVM_COV() {
+  static ConstString g_section_name("__LLVM_COV");
+  return g_section_name;
+}
+
 ConstString ObjectFileMachO::GetSectionNameEHFrame() {
   static ConstString g_section_name_eh_frame("__eh_frame");
   return g_section_name_eh_frame;
@@ -6145,6 +6150,13 @@ bool ObjectFileMachO::SectionIsLoadable(const Section *section) {
     return false;
   if (GetModule().get() != section->GetModule().get())
     return false;
+  // firmware style binaries with llvm gcov segment do
+  // not have that segment mapped into memory.
+  if (section->GetName() == GetSegmentNameLLVM_COV()) {
+    const Strata strata = GetStrata();
+    if (strata == eStrataKernel || strata == eStrataRawImage)
+      return false;
+  }
   // Be careful with __LINKEDIT and __DWARF segments
   if (section->GetName() == GetSegmentNameLINKEDIT() ||
       section->GetName() == GetSegmentNameDWARF()) {
diff --git a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.h b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.h
index 0a47f3a7dd1861..55bc688126eb36 100644
--- a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.h
+++ b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.h
@@ -271,6 +271,7 @@ class ObjectFileMachO : public lldb_private::ObjectFile {
   static lldb_private::ConstString GetSegmentNameOBJC();
   static lldb_private::ConstString GetSegmentNameLINKEDIT();
   static lldb_private::ConstString GetSegmentNameDWARF();
+  static lldb_private::ConstString GetSegmentNameLLVM_COV();
   static lldb_private::ConstString GetSectionNameEHFrame();
 
   llvm::MachO::dysymtab_command m_dysymtab;

``````````

</details>


https://github.com/llvm/llvm-project/pull/86359