elf: fix symbol resolution order to use load order

This fixes an issue where a symbol exists in multiple objects; when just
one is loaded it is resolved to one of the modules, but after the second is
loaded, it resolves to the second.  To the program this appears as if the
address or contents of a static variable has changed.

In our case this was triggered by both statically and dynamically linking
a library.

core/elf.cc

@@ -560,6 +560,9 @@ namespace elf {
     void program::set_object(std::string name, elf_object* obj)
     {
         _files[name] = obj;
+        if (std::find(_modules.begin(), _modules.end(), obj) == _modules.end()) {
+            _modules.push_back(obj);
+        }
     }
 
     elf_object* program::add_object(std::string name)
@@ -572,6 +575,7 @@ namespace elf {
             auto ef = new elf_file(*this, f, name);
             ef->set_base(_next_alloc);
             _files[name] = ef;
+            _modules.push_back(ef);
             ef->load_segments();
             _next_alloc = ef->end();
             add_debugger_obj(ef);
@@ -589,6 +593,7 @@ namespace elf {
         auto ef = _files[name];
 
 	_files.erase(name);
+	_modules.erase(std::find(_modules.begin(), _modules.end(), ef));
 	ef->unload_segments();
 	delete ef;
     }
@@ -606,10 +611,9 @@ namespace elf {
 
     symbol_module program::lookup(const char* name)
     {
-        // FIXME: correct lookup order?
-        for (auto name_module : _files) {
-            if (auto sym = name_module.second->lookup_symbol(name)) {
-                return symbol_module(sym, name_module.second);
+        for (auto module : _modules) {
+            if (auto sym = module->lookup_symbol(name)) {
+                return symbol_module(sym, module);
             }
         }
         return symbol_module(nullptr, nullptr);
@@ -630,10 +634,7 @@ namespace elf {
     void program::with_modules(std::function<void (std::vector<elf_object*>&)> f)
     {
         // FIXME: locking?
-        std::vector<elf_object*> tmp;
-        for (auto& name_module : _files) {
-            tmp.push_back(name_module.second);
-        }
+        std::vector<elf_object*> tmp = _modules;
         f(tmp);
     }
 

include/elf.hh

@@ -342,6 +342,7 @@ namespace elf {
         void* _next_alloc;
         std::unique_ptr<elf_object> _core;
         std::map<std::string, elf_object*> _files;
+        std::vector<elf_object*> _modules; // in priority order
         // debugger interface
         static elf_object* s_objs[100];
     };