[LLDB][ELF] Load both, .symtab and .dynsym sections

Summary:
This change ensures that the .dynsym section will be parsed even when there's already is a .symtab.

It is motivated because of minidebuginfo (https://sourceware.org/gdb/current/onlinedocs/gdb/MiniDebugInfo.html#MiniDebugInfo).

There it says:

    Keep all the function symbols not already in the dynamic symbol table.

That means the .symtab embedded inside the .gnu_debugdata does NOT contain the symbols from .dynsym. But in order to put a breakpoint on all symbols we need to load both. I hope this makes sense.

My other patch D66791 implements support for minidebuginfo, that's why I need this change.

Reviewers: labath, espindola, alexshap

Subscribers: JDevlieghere, emaste, arichardson, MaskRay, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D67390

llvm-svn: 371599

1 files changed, 18 insertions, 8 deletions

diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
index e507f0e4d74..20e26f033d1 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -2647,21 +2647,31 @@ Symtab *ObjectFileELF::GetSymtab() {
     // smaller version of the symtab that only contains global symbols. The
     // information found in the dynsym is therefore also found in the symtab,
     // while the reverse is not necessarily true.
+    // One exception to the above rule is when we have minidebuginfo embedded
+    // into a compressed .gnu_debugdata section. This section contains a .symtab
+    // from which all symbols already contained in the .dynsym are stripped.
     Section *symtab =
         section_list->FindSectionByType(eSectionTypeELFSymbolTable, true).get();
-    if (!symtab) {
-      // The symtab section is non-allocable and can be stripped, so if it
-      // doesn't exist then use the dynsym section which should always be
-      // there.
-      symtab =
-          section_list->FindSectionByType(eSectionTypeELFDynamicSymbols, true)
-              .get();
-    }
     if (symtab) {
       m_symtab_up.reset(new Symtab(symtab->GetObjectFile()));
       symbol_id += ParseSymbolTable(m_symtab_up.get(), symbol_id, symtab);
     }
 
+    // The symtab section is non-allocable and can be stripped, while the dynsym
+    // section which should always be always be there. If both exist we load
+    // both to support the minidebuginfo case. Otherwise we just load the dynsym
+    // section.
+    Section *dynsym =
+        section_list->FindSectionByType(eSectionTypeELFDynamicSymbols, true)
+            .get();
+    if (dynsym) {
+      if (!m_symtab_up) {
+        auto sec = symtab ? symtab : dynsym;
+        m_symtab_up.reset(new Symtab(sec->GetObjectFile()));
+      }
+      symbol_id += ParseSymbolTable(m_symtab_up.get(), symbol_id, dynsym);
+    }
+
     // DT_JMPREL
     //      If present, this entry's d_ptr member holds the address of
     //      relocation