197 questions
1
vote
0
answers
76
views
dlsym Not using the symbols loaded by handle, but those already known instead [closed]
I have a project written in C++ which consists in a main application which loads a few plugins. The overview of the problem is as follows:
The plugins, which are shared objects (.so), load without any ...
- 361
2
votes
1
answer
89
views
dlsym interception with AddressSanitizer causes a DEADLYSIGNAL
I'm trying to intercept dlsym calls using LD_PRELOAD. To debug the library, I am building it with AddressSanitizer. The resulting behavior is inconsistent, however: sometimes it works as expected, but ...
- 33
1
vote
1
answer
71
views
Is there a standard for creating shared libraries with 'conditional' or 'soft' dependencies on other shared libraries?
I'm writing an application fooapp which can use one of several other, existing libraries for some part of its functionality. For the sake of discussion, let's say that its saving the program output. ...
- 137k
1
vote
1
answer
155
views
Is there a compiler flag which allows a shared library to call a function coming from the shared library which opened it?
Below is a minimal reproducible example, where the goal is to call b_util() from a(). My question is whether it's possible to do this without explicitly passing a b_util() function pointer to a.c.
I ...
- 672
2
votes
1
answer
106
views
How to call a function dynamically in executable file itself?
I was trying call a function dynamically in an executable file itself.
The target function test_func was coded with the main function in the same source file. Here is the sample code:
#include <...
- 128
3
votes
1
answer
81
views
How to override php_network_connect_socket_to_host in PHP with LD_PRELOAD and dlsym?
I am trying to override "php_network_connect_socket_to_host" and cannot do it, although I am able to override "connect".
Here is the source code of wrapper.c:
#define _GNU_SOURCE 1
...
- 33
1
vote
1
answer
135
views
When is late enough to use dlsym to find functions in another shared library?
Say I have an application foo that is linked against bar.so. I have another library, buzz.so that the application does not directly link, but that I use when I run the application with LD_PRELOAD like ...
- 22.3k
0
votes
0
answers
90
views
Identifying which global variable is allocated by which shared library
Assume there are shared libraries lib1, lib2, etc. each declaring and using one of its own global variable g_lib1, g_lib2, etc. I have the addresses of g_lib1, g_lib2, etc., as well as the names of ...
- 11
0
votes
0
answers
213
views
Calling JNI_CreateJavaVM just hangs
Just trying debug what wrong with harness code, which was compiled with command:
┌──(kali㉿kali)-[~/…/experimment/research/PoCs/android-afl-qemu]
└─$ export CC=/home/kali/Android/Sdk/ndk/22.1.7171670/...
- 25
4
votes
1
answer
132
views
Man page workaround for dlsym() still error prone?
I was reading the man page to dlopen(), and I stumbled on this block of code:
cosine = (double (*)(double)) dlsym(handle, "cos");
/* According to the ISO C standard, casting ...
0
votes
1
answer
93
views
Casting a dlsym'd function pointer to to same function signature but changed parameter definition
Let's say I have a struct defined in MyType.h
struct MyType {
int x;
int y;
};
And I build a lib myLib.so which exposes a function that takes the above type as a parameter.
#include "...
- 45
0
votes
1
answer
255
views
How to isolate the runtime of a dynamic loaded library (dlopen)
Take for instance an application that needs to load several other shared libraries. Each with the same interface. How can I prevent that a crash in any of the loaded shared libraries to not crash the ...
1
vote
2
answers
84
views
What are the scoping rules for subsequent calls to dlopen?
Suppose I have an executable that dlopens libfirst.so with RTLD_LOCAL which then dlopens libsecond.so with RTLD_GLOBAL. Should the symbols from libsecond.so now be directly available (i.e., without ...
- 2,023
0
votes
1
answer
174
views
Using dlopen and dlsym with a third party c++ library
Newbie question. Suppose there is a third party library ClassLibrary.so, which contains the class definition of a ClassTest and I don't have access to the source of ClassLibrary.so. Can I use ...
- 41
2
votes
3
answers
928
views
Conflicting C linkage declaration of two functions in different C++ namespaces
In C++ code, I would like to be able to include two headers for two different versions of a shared C library that I load at runtime (with dlopen/dlsym on linux, GetProcAddress on windows).
For one ...
- 442
2
votes
0
answers
54
views
What does DlsymWeak::initialize do in rust?
I have a program that calls libc::memchr many times. When profiling my code I see that
the function using the most time is DlsymWeak::initialize. initialize seem to be called by memchr, which is ...
- 1,948
1
vote
1
answer
158
views
dlsym causing segfault when dynamically loading shm_open
I am trying to figure out to load the function shm_open dynamically at runtime and have hit a wall.
My current code is as such:
CMakeLists.txt
project(dlsysm_stack_overflow_example)
...
- 13
0
votes
1
answer
548
views
How do I get a function name in the symbol table to point to a different function?
On MacOS Ventura, obtaining a handle to the dynamic loader using dlopen(NULL, 0) returns a handle containing the entire executable's symbol table. Using this handle, one can obtain pointers to symbol ...
- 49
2
votes
1
answer
78
views
A complicated situation while using dlsym casting
In our code there is a function defined as:
a.h
extern int (*get_prof_action(void))(void);
a.c
static int (*ProfAction)(void) = NULL;
int (*get_prof_action(void))(void)
{
return ProfAction;
}
...
- 67
2
votes
1
answer
235
views
dlsym how do I pass the implicit "this" pointer in nonstatic member function?
I want to call a function with dlsym and it is a member function of an object, I have the pointer, but it is not working. The function lives in the main executable, and I am loading it from a shared ...
-1
votes
1
answer
657
views
Why calling dlopen sometimes breaks my application by damaging class variables content?
I am trying to load library with dlopen().
But call to this dlopen() function sometimes (not always) damages my class variables and then app goes to segmentation fault.
Below is not precise code (...
- 123
2
votes
1
answer
357
views
What is the C++ way of interpreting the void* returned by dlsym as a pointer-to-function?
Assume a dynamic library exports a function, e.g. of type void(), named foo. A client code could then make use of it like in the following snippet (assuming foo is exposed via extern "C" ...
- 30.3k
3
votes
1
answer
445
views
How to handle different behaviour for dlsym() in OSX and Linux (generic)
I recently added some dynamic plugin behavior in an OSX program which works as designed. However, trying the same on Linux (generic) fails as dlsym() library call fails to resolve symbol in the same ...
- 397
0
votes
1
answer
234
views
return address of dlsym and Address of Function Pointer assigned
void* l = dlsym(lib,"_ZN11Environment9LibLogger14log_processingEiNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEjS6_z");
*(void **)&log_fcn = l;
std::cout<<"Address&...
3
votes
0
answers
218
views
Is it possible to define a symbol dynamically such that it will be found by dlsym?
I want to simulate loading symbols from a shared library for testing purposes.
Is there a way to define a symbol at runtime programmatically such that dlsym will find it?
For example:
...
- 5,819
0
votes
1
answer
911
views
(solved) C++ Load one Shared Object with dependencies and access their functions
OS Linux Ubuntu 18.04, gcc 7.4.0
A program should load one SO which is dependent on other SOs. All exported functions of all SOs should be called by the program.
I found serveral related questions ...
- 203
1
vote
1
answer
878
views
Error while importing pynput - dlsym(0x7f90f7d0c310, PyObjCObject_New): symbol not found
I installed pynput module (version 1.7.4) using this command: pip3 install pynput
I tried to import the module in my Jupyter-lab, which always ended up a failure. The error message looks like this:
...
- 31
1
vote
1
answer
348
views
Hooking functions located in the executable (not in shared libraries)
Let's say I have a function foo in ./elf.
I want to hook it with foo_hook which is located in my shared object.
foo is not exported from ./elf.
LD_PRELOAD is useful for hooking functions in shared ...
- 11
2
votes
1
answer
296
views
Wrap clone syscall using LD_PRELOAD
Variatic functions such as printf can be wrapped using dlsym because it has a va_list version vprintf.
So,
int printf(const char *format, ...); //is equivalent to
int vprintf(const char *format, ...
- 41
3
votes
2
answers
1k
views
dlsym() + RTLD_NEXT doesn't work as expected on Ubuntu 20.04
I'm faced a strange runtime behavior on Ubuntu 20.04 (gcc v 9.3.0) when using dlsym() call.
Please, see below a simple example:
file test.cpp:
#include <iostream>
#include <dlfcn.h>
#...
- 505
0
votes
1
answer
361
views
When a C application uses a shared library, is it possible to retrieve the bss and data sections of that shared library
Application written in C, and runs on Ubuntu 18.04.
This application links with couple of shared libraries, lets say shared_lib1_external.so,
and shared_lib1_internal.so.
I have this unique scenario ...
- 19
-1
votes
3
answers
161
views
Line number of the caller of a preloaded library function
Let's say I have a program (program.c) that uses rand function in standard C library.
1 #include <stdlib.h>
2 int main(){
3 int rand_number = rand();
4 }
I also have a shared library (...
- 380
0
votes
0
answers
17
views
Calling dlsym from a function other than _start crashes [duplicate]
I have this assembly program that works fine:
SECTION .text
EXTERN dlopen ; loads a dynamic library
EXTERN dlsym ; retrieves the address for a symbol in the dynamic library
global _start ; "...
- 4,159
0
votes
1
answer
369
views
dlsym crash when called from assembler
I have a small program in assembler that loads an .so file using dlopen, and then tries to load a function pointer using dlsym. Calling dlopen seems to be fine but it crashes when I call dlsym.
...
- 4,159
3
votes
2
answers
1k
views
Library interpositioning
I have been trying to intercept calls to malloc and free, following our textbook (CSAPP book).
I have followed their exact code, and nearly the same code that I found online and I keep getting a ...
- 47
2
votes
1
answer
1k
views
How in C to get the name of the shared library a symbol is loaded from programatically at runtime?
I load a symbol from a shared library like this:
void *sym = dlsym(RTLD_DEFAULT, "printf");
That will tell me whether the symbol printf exists in a loaded shared library, and if it does, ...
- 5,588
1
vote
1
answer
811
views
this dlsym call runs into a segfault (when caller .so is the same as target .so)
First, the problem:
Thread 2 "lexe.exe" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff2c89700 (LWP 17367)]
do_lookup_x (undef_name=undef_name@entry=0x7fffeb893ad9 &...
- 23.6k
1
vote
0
answers
817
views
Getting segmentation fault while using dlsym after dlmopen but with dlopen dlsym works fine
I am getting issues with dlmopen, but I have successfully used dlopen and dlsym in my cpp program (in linux)
void *lib_handle = dlopen(lib_path, RTLD_NOW);
After this I used dlsym to get the function
...
2
votes
0
answers
499
views
Any way to grab struct from DLL using dlsym (Dynamic Linking) without header file (.h)?
I have been looking everywhere for this question, but I cannot seem to get the answer for this.
So, every example I have been to is simply how to grab function pointers from SO file, which I have done....
- 48
2
votes
1
answer
1k
views
Loading a C++ class with polymorphism using dlsym()
I have a C++ program which I need to open a shared object (.so) and load a C++ class from it. I have seen this done on the internet and I have loaded many things using dlsym() in both C and C++, so I ...
- 444
0
votes
0
answers
180
views
How to modify symbol address in so
I have a liba.so.
the a.h is:
#pragma once
#include <functional>
extern "C" {
void set_loop_func(std::function<void()> fn);
int create_thread();
}
the a.cpp is:
#include &...
0
votes
0
answers
301
views
How to cover RTLD_DEEPBIND
I would like to dlopen() a dynamic library liba_new.so which was created by g++ ../include/a.cpp -fPIC -shared -o liba_new.so -std=c++11 -lpthread. But in the application loading it, i will hook the ...
1
vote
1
answer
607
views
Using dlsym() to stub malloc/free leads to segmentation fault
I started to dabble in unit testing C code (using check) and stubbing functions. I am trying to unit
test a small library of data structures that I wrote and wanted to test how it would react to OOM. ...
- 57
1
vote
2
answers
83
views
How can understand the *(void **)(&m_handle) = dlsym("./haldle_lib.so", "custom_func");
Just want to understand the following code:
Why we use option (1) other than option (2)? I don't know what's the use of (void**) here? really confused.
Class Handle{
private:
int unique_id;
...
- 151
0
votes
1
answer
321
views
How to use my c style func obtained by dlsym in my c++ program
SO basically i dont know hu use this funciton "createLib" i can't seem to be able to use it:
auto createLibFunc = dlsym(lib, symbol.c_str());
This works, i opened my dymacally loaded lib with dlopen, ...
1
vote
0
answers
583
views
Multiple dlopen and RTLD_NEXT
I have an executable (1) with two shared objects (2 and 3) opened using dlopen(..., RTLD_GLOBAL). All files include the symbol func().
If I use dlsym(RTLD_NEXT, ...) in 1 looking for the next func() ...
- 19
0
votes
1
answer
3k
views
Undefined symbol for dlsym in C++ [duplicate]
I have one C++ program which I want to load into my current running C++ program. Following are the snippet
File : a.cpp
#include<bits/stdc++.h>
using namespace std;
void abc() {
...
2
votes
2
answers
989
views
blocking call to `dlsym` (RTLD_NEXT)
I am trying to wrap function. To do that I thought about using dlsym to get the real function location in memory after having injected my dynamic library.
I am running on MacOS Mojave (10.14.6) with ...
- 53
2
votes
2
answers
2k
views
How to dynamically load and call a symbol which has a library-specific type as a function parameter
Suppose I have the following:
// lib1.h
struct S
{
int x;
};
void f(S* s); // defined in .cpp
and
// lib2.h
struct S
{
int x;
int y;
};
void f(S* s); // defined in .cpp
Resulting in ...
- 38.5k
7
votes
2
answers
3k
views
Calling dlsym() with a NULL handle doesn't return NULL, but rather returns a random function
My title may not be clear, so allow me to explain. I have a piece of code that goes like this:
void* pluginFile = dlopen(fileName, RTLD_LAZY);
auto function = dlsym(pluginFile, "ExpectedFunction");
...
- 599