Android dynamic_cast not work when dynamic loading from shared libraries

Issue

I am experiencing dynamic_cast issue when porting vsomeip to Android.

In order to simplify the case, I created a rather simple test app/lib structure as below:

It contains a lib and an app:

• libbase_1.so: implement class Final which inherrit from Base_1 and Base_2, provides get() to return std::shared<Base_1>

• test_app: dynamic loading libbase_1.so (by dl_open), get std::shared<Base>, and dynamic cast to std::shared<Base_2>.

The dynamic cast works well on x86 and other arm platforms(e.g.: use linaro toolchain); but failed to work on Android, it always get nullptr.

The environemt of the AOSP is:

• NDK Version: R18
• Build sytem: AOSP
• Host OS: Ubuntu 18.04
• Compiler: Clang++ (9.0.3)
• TARGET_ARCH: armv8a

I have followed some reference below but all do not work:

• Android NDK + Two Shared Libraries + RTTI + Dynamic cast = Impossible
• https://android.googlesource.com/platform/ndk/+/master/docs/user/common_problems.md#rtti_exceptions-not-working-across-library-boundaries
• https://github.com/android/ndk/issues/533#issuecomment-335977747

Does anyone have idea? Thanks a lot~~

---

The complete runnable src can be downloaded from: https://drive.google.com/file/d/1YNsZVPVIn7_y247byBfl6JaTVtjR6tYn/view?usp=sharing

And also pastes here:

//Android.bp: can be build directly by mm

libbase_1_srcs = [
   "src_1.cpp",
   "src_2.cpp",
   "src_3.cpp",
   "lib_1.cpp",
]

main_srcs = [
   "main.cpp",
   "src_1.cpp",
   "src_2.cpp",
]

cc_defaults {
    name: "test_cast_defaults",
    cppflags: [
   "-std=c++11",
   "-frtti",
    ]
}

cc_library_shared {
    name: "libbase_1",
    vendor: true,
    srcs: libbase_1_srcs,
    defaults: [
        "test_cast_defaults"
    ],
    rtti: true,
}

cc_binary {
    name: "test_cast",
    srcs: main_srcs,
    vendor: true,
    defaults: [
        "test_cast_defaults"
    ],
    shared_libs: [
    ],
    rtti: true,
}

//CMakeLists.txt: test for X86 or others

cmake_minimum_required(VERSION 3.1)
set(project_name "test_cast")
project(${project_name})

add_library(base_1 SHARED lib_1.cpp src_1.cpp src_2.cpp src_3.cpp)
target_include_directories(base_1 PUBLIC ${${project_name}_SOURCE_DIR}/)

add_executable(test_cast main.cpp src_1.cpp src_2.cpp)
target_include_directories(test_cast PUBLIC ${${project_name}_SOURCE_DIR}/)
target_link_libraries(test_cast PUBLIC dl)

//main.cpp

#include <dlfcn.h>
#include <iostream>
#include "lib_1.h"
#include <memory>

#define libname "libbase_1.so"
#define funcname "get_plugin"

int main(void)
{
    void *handle = dlopen(libname, RTLD_LAZY | RTLD_GLOBAL);
    void *func;
    if (handle == nullptr) {
        std::cout << "Can not find: " << libname << std::endl;
        return -1;
    }
    func = dlsym(handle, funcname);
    const char *dlsym_error = dlerror();
    if (dlsym_error) {
        std::cout << "dlsym err: " << dlsym_error <<std::endl;
        return -1;
    }

    plugin_init_func func_get = reinterpret_cast<plugin_init_func>(func);
    get_plugin_func func_create = (*func_get)();

    auto base_1 = (*func_create)();
    auto base_2 = std::dynamic_pointer_cast<Base_2>(base_1);

    if (base_2) {
        std::cout << "dl: dynamic cast success!" << std::endl;
    } else {
        std::cout << "dl: dynamic cast failed!" << std::endl;
    }
    return 0;
}

//lib_1.cpp

#include "lib_1.h"

get_plugin_func get_plugin(void)
{
    return Final::get;
}

//lib_1.h

#ifndef __LIB_1_H__
#define __LIB_1_H__
#include "header_3.h"
typedef std::shared_ptr<Base_1> (*get_plugin_func)();
typedef get_plugin_func (*plugin_init_func)();
extern "C" {
    get_plugin_func get_plugin(void);
};
#endif

//header_1.h

#ifndef __HEADER_1__
#define __HEADER_1__
class Base_1 {
public:
    virtual ~Base_1();
};
#endif

//header_2.h

#ifndef __HEADER_2__
#define __HEADER_2__
class Base_2 {
public:
    virtual ~Base_2();
};
#endif

//header_3.h

#ifndef __HEADER_3__
#define __HEADER_3__
#include "header_1.h"
#include "header_2.h"
#include <iostream>
#include <memory>
class Final : public Base_2,
              public Base_1 {
public:
    static std::shared_ptr<Base_1> get(void) {
        std::shared_ptr<Base_1> base_1 = std::make_shared<Final>();
        auto base_2 = std::dynamic_pointer_cast<Base_2>(base_1);
        if (base_2) {
            std::cout << "in lib: dynamic cast success!" << std::endl;
        } else {
            std::cout << "in lib: dynamic cast failed!" << std::endl;
        }
        return base_1;
    }
    ~Final();
};
#endif

//src_1.cpp

#include <header_1.h>
#include <iostream>
Base_1::~Base_1()
{
    std::cout << "in: " << __func__ << std::endl;
}

//src_2.cpp

#include "header_2.h"
#include <iostream>
Base_2::~Base_2()
{
    std::cout << "in: " << __func__ << std::endl;
}

//src_3.cpp

#include "header_3.h"
#include <iostream>
Final::~Final() {
    std::cout << "in: " << __func__ << std::endl;
}

---

Succcess Run(X86):

in lib: dynamic cast success!
dl: dynamic cast success!
in: ~Final
in: ~Base_1
in: ~Base_2

Failure Run(Android):

in lib: dynamic cast success!
dl: dynamic cast failed!
in: ~Final
in: ~Base_1
in: ~Base_2

Solution

I had the same issue when I used CommonAPI via vsomeip with clang compiler and only workaround helped me to fix it. More details here: https://github.com/nkh-lab/genivi-capi-someip-examples/blob/ndk/CMakeLists.txt

The problem is that we have the same typeinfo for vsomeip_v3::configuration_plugin in libvsomeip3.so and libvsomeip3-cfg.so and dynamic_pointer_cast uses the wrong one (for example first entry in typeinfo table). So, we need to change the loading order of mentioned libraries and after that dynamic_pointer_cast will use correct one.

Also answered in GENIVI/vsomeip/issues

Answered By - Mykola Khyliuk