Support looking up absolute symbols

[aprantl]

Summary

The Swift stdlib uses absolute symbols in the dylib to communicate feature flags to the process. LLDB's expression evaluator needs to be able to find them. This wires up absolute symbols so they show up in the symtab lookup command, which is also all that's needed for them to be visible to the expression evaluator JIT.

rdar://85093828

[JDevlieghere]

LGTM

lldb/source/Symbol/Symbol.cpp

void Symbol::Clear() {
   m_contains_linker_annotations = false;
   m_is_weak = false;
   m_type = eSymbolTypeInvalid;
   m_flags = 0;
   m_addr_range.Clear();
 }
 
 bool Symbol::ValueIsAddress() const {
-  return m_addr_range.GetBaseAddress().GetSection().get() != nullptr;
+  return m_addr_range.GetBaseAddress().GetSection().get() != nullptr ||
+         m_type == eSymbolTypeAbsolute;
 }
 
 ConstString Symbol::GetDisplayName() const {
   return GetMangled().GetDisplayDemangledName();
 }
 
 ConstString Symbol::GetReExportedSymbolName() const {
   if (m_type == eSymbolTypeReExported) {

lldb/source/Symbol/Symtab.cpp

if (temp_symbol_indexes_size > 0) {
       for (unsigned i = 0; i < temp_symbol_indexes_size; i++) {
         SymbolContext sym_ctx;
         sym_ctx.symbol = SymbolAtIndex(temp_symbol_indexes[i]);
         if (sym_ctx.symbol) {
           switch (sym_ctx.symbol->GetType()) {
           case eSymbolTypeCode:
           case eSymbolTypeResolver:
           case eSymbolTypeReExported:
+          case eSymbolTypeAbsolute:
             symbol_indexes.push_back(temp_symbol_indexes[i]);
             break;
           default:
             break;
           }
         }
       }
     }

lldb/test/Shell/SymbolFile/absolute-symbol.s

+# RUN: %clang %s -g -c -o %t.o
+# RUN: %lldb -b -o 'target modules lookup -s absolute_symbol' %t.o | FileCheck %s
+# CHECK: 1 symbols match 'absolute_symbol'
+# CHECK:   Address: 0x0000000012345678 (0x0000000012345678)
+# CHECK:   Summary: 0x0000000012345678
+.globl absolute_symbol
+absolute_symbol = 0x12345678