Demos: Add "DynamicObjectDemo" to demo the dynamic loader

Author: https://github.com/itamar8910
Commit: https://github.com/SerenityOS/serenity/commit/09ccdc697b0
Pull-request: https://github.com/SerenityOS/serenity/pull/3738
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/awesomekling

Demos/CMakeLists.txt

@@ -1,4 +1,5 @@
 add_subdirectory(Cube)
+add_subdirectory(DynamicObject)
 add_subdirectory(DynamicLink)
 add_subdirectory(Eyes)
 add_subdirectory(Fire)

Demos/DynamicObject/CMakeLists.txt

@@ -0,0 +1,11 @@
+set(SOURCES
+    main.cpp
+    ../../Libraries/LibC/crt0_shared.cpp
+)
+
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -nostartfiles -pie -fpic")
+
+serenity_bin(DynamicObjectDemo)
+target_link_libraries(DynamicObjectDemo SampleLib LibCShared)
+
+add_subdirectory(SampleLib)

Demos/DynamicObject/SampleLib/CMakeLists.txt

@@ -0,0 +1,11 @@
+
+set(SOURCES
+    lib.cpp
+)
+
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -nostdlib -fpic") 
+
+add_library(SampleLib SHARED ${SOURCES})
+target_link_libraries(SampleLib LibCShared)
+#target_link_libraries(SampleLib)
+install(TARGETS SampleLib DESTINATION usr/lib)

Demos/DynamicObject/SampleLib/lib.cpp

@@ -0,0 +1,20 @@
+
+#include "../lib.h"
+
+int func();
+
+__thread int g_tls1 = 0;
+__thread int g_tls2 = 0;
+
+static void init_function() __attribute__((constructor));
+
+void init_function()
+{
+    g_tls1 = 1;
+    g_tls2 = 2;
+}
+
+int func()
+{
+    return 3;
+}

Demos/DynamicObject/main.cpp

@@ -0,0 +1,24 @@
+#include "lib.h"
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/internals.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+int main(int argc, char** argv, char** env)
+{
+    (void)argc;
+    (void)argv;
+    (void)env;
+
+    printf("Well Hello Friends!\n");
+    printf("trying to open /etc/fstab for writing..\n");
+    int rc = open("/etc/fstab", O_RDWR);
+    if (rc == -1) {
+        int _errno = errno;
+        perror("open failed");
+        printf("rc: %d, errno: %d\n", rc, _errno);
+        return func() + g_tls1 + g_tls2;
+    }
+}

Libraries/LibC/CMakeLists.txt

@@ -1,7 +1,7 @@
 set(LIBC_SOURCES
     arpa/inet.cpp
     assert.cpp
-    crt0.cpp
+    #crt0.cpp
     ctype.cpp
     cxxabi.cpp
     dirent.cpp
@@ -69,3 +69,6 @@ set(SOURCES ${LIBC_SOURCES} ${AK_SOURCES} ${ELF_SOURCES})
 serenity_libc(LibC c)
 target_link_libraries(LibC crt0)
 add_dependencies(LibC LibM)
+
+add_library(LibCShared SHARED ${SOURCES})
+install(TARGETS LibCShared DESTINATION usr/lib)

Libraries/LibC/crt0_shared.cpp

@@ -0,0 +1,30 @@
+#include <AK/Types.h>
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/internals.h>
+#include <unistd.h>
+
+extern "C" {
+
+int main(int, char**, char**);
+
+extern void __libc_init();
+extern void _init();
+extern char** environ;
+extern bool __environ_is_malloced;
+
+int _start(int argc, char** argv, char** env);
+int _start(int argc, char** argv, char** env)
+{
+    // asm("int3");
+    environ = env;
+    __environ_is_malloced = false;
+
+    __libc_init();
+    _init();
+
+    int status = main(argc, argv, environ);
+    return status;
+}
+}