Lookup symbol deeper

dlsym function doesn't seem to lookup symbol deep enough. This
patch includes a bfs version of collect dependencies. It
fixes test_dlsym_from_sofile_with_preload and
dlsym_with_dependencies.

Signed-off-by: Waldemar Kozaczuk <jwkozaczuk@gmail.com>
Signed-off-by: Zhiting Zhu <zhitingz@cs.utexas.edu>
Message-Id: <20200120011727.1736-1-zhitingz@cs.utexas.edu>

Author: photoszzt

core/elf.cc

@@ -27,6 +27,7 @@
 #include <sys/utsname.h>
 #include <osv/demangle.hh>
 #include <boost/version.hpp>
+#include <deque>
 
 #include "arch.hh"
 
@@ -950,6 +951,22 @@ Elf64_Sym* object::lookup_symbol(const char* name, bool self_lookup)
     return sym;
 }
 
+symbol_module object::lookup_symbol_deep(const char* name)
+{
+    symbol_module sym = { lookup_symbol(name, false), this };
+    if (!sym.symbol) {
+        auto deps = this->collect_dependencies_bfs();
+        for (auto&& _obj : deps) {
+            auto symbol = _obj->lookup_symbol(name, false);
+            if (symbol) {
+                sym = { symbol, _obj };
+                break;
+            }
+        }
+    }
+    return sym;
+}
+
 unsigned object::symtab_len()
 {
     if (dynamic_exists(DT_HASH)) {
@@ -1089,6 +1106,28 @@ void object::collect_dependencies(std::unordered_set<elf::object*>& ds)
     }
 }
 
+std::deque<elf::object*> object::collect_dependencies_bfs()
+{
+    std::unordered_set<object*> deps_set;
+    std::deque<object*> operate_queue;
+    std::deque<object*> deps;
+    operate_queue.push_back(this);
+    deps_set.insert(this);
+
+    while (!operate_queue.empty()) {
+        object* obj = operate_queue.front();
+        operate_queue.pop_front();
+        deps.push_back(obj);
+        for (auto&& d : obj->_needed) {
+            if (!deps_set.count(d.get())) {
+                deps_set.insert(d.get());
+                operate_queue.push_back(d.get());
+            }
+        }
+    }
+    return deps;
+}
+
 std::string object::soname()
 {
     return dynamic_exists(DT_SONAME) ? dynamic_str(DT_SONAME) : std::string();

include/osv/elf.hh

@@ -347,6 +347,7 @@ public:
     void* base() const;
     void* end() const;
     Elf64_Sym* lookup_symbol(const char* name, bool self_lookup);
+    symbol_module lookup_symbol_deep(const char* name);
     void load_segments();
     void process_headers();
     void unload_segments();
@@ -405,6 +406,7 @@ private:
     void relocate_pltgot();
     unsigned symtab_len();
     void collect_dependencies(std::unordered_set<elf::object*>& ds);
+    std::deque<elf::object*> collect_dependencies_bfs();
     void prepare_initial_tls(void* buffer, size_t size, std::vector<ptrdiff_t>& offsets);
     void prepare_local_tls(std::vector<ptrdiff_t>& offsets);
     void alloc_static_tls();

libc/dlfcn.cc

@@ -74,7 +74,7 @@ void* dlsym(void* handle, const char* name)
         abort();
     } else {
         auto obj = *reinterpret_cast<std::shared_ptr<elf::object>*>(handle);
-        sym = { obj->lookup_symbol(name, false), obj.get() };
+        sym = obj->lookup_symbol_deep(name);
     }
     if (!sym.obj || !sym.symbol) {
         dlerror_fmt("dlsym: symbol %s not found", name);

tests/tst-dlfcn.cc

@@ -13,7 +13,7 @@
 namespace utf = boost::unit_test;
 
 const bool rtld_next = false;
-const bool deep_lookup = false;
+const bool deep_lookup = true;
 
 static bool called = false;
 extern "C" void DlSymTestFunction()