[Lldb-commits] [lldb] [LLDB][ELF] Fix section unification to not just use names. (PR #90099)

[Pavel Labath via lldb-commits]

================
@@ -1854,6 +1854,49 @@ class VMAddressProvider {
 };
 }
 
+namespace {
+  // We have to do this because ELF doesn't have section IDs, and also
+  // doesn't require section names to be unique.  (We use the section index
+  // for section IDs, but that isn't guaranteed to be the same in separate
+  // debug images.)
+  SectionSP FindMatchingSection(const SectionList &section_list,
+                                SectionSP section) {
+    SectionSP sect_sp;
+
+    addr_t vm_addr = section->GetFileAddress();
+    ConstString name = section->GetName();
+    offset_t file_size = section->GetFileSize();
+    offset_t byte_size = section->GetByteSize();
+    SectionType type = section->GetType();
+    bool thread_specific = section->IsThreadSpecific();
+    uint32_t permissions = section->GetPermissions();
+    uint32_t alignment = section->GetLog2Align();
+
+    for (auto sect_iter = section_list.begin();
+         sect_iter != section_list.end();
+         ++sect_iter) {
+      if ((*sect_iter)->GetName() == name
+          && (*sect_iter)->GetType() == type
+          && (*sect_iter)->IsThreadSpecific() == thread_specific
+          && (*sect_iter)->GetPermissions() == permissions
+          && (*sect_iter)->GetFileSize() == file_size
+          && (*sect_iter)->GetByteSize() == byte_size
+          && (*sect_iter)->GetFileAddress() == vm_addr
+          && (*sect_iter)->GetLog2Align() == alignment) {
----------------
labath wrote:

Am I correct in understanding that this code is used when unifying the sections of a separate debug file with a stripped file? If so, then I believe this comparison is too strict. An object file produced by `objcopy --only-keep-debug` will only have placeholder sections instead of the sections that contained actual code. That means (at least) their file size and file offset will be different from that in the original file.

I think it would be sufficient to use the file address (called virtual address in ELF), possibly confirmed by section name, as the unification key.

https://github.com/llvm/llvm-project/pull/90099