- How to link and compile with .so file in Linux
- 3 Answers 3
- How Do so (Shared Object) Filenames Work in Linux
- What are Shared Objects (so) Files?
- How Shared Object Filenames Work
- Examples of Shared Object Filenames
- libcrypto.so.1.1
- libssl.so.1.1
- libX11.so.6
- libgtk-3.so.0
- How Shared Object Files are Found
- Benefits of Shared Objects
- Major vs. Minor Version Numbers
- Managing Shared Objects
- Conclusion
- Why are .so files executable? [duplicate]
- 2 Answers 2
- How to open the files with the extension («.so») [closed]
- 2 Answers 2
How to link and compile with .so file in Linux
I am having .c and .so file. I tried by using the following compilation: gcc main.c -ldl . In that .c file i linked to .so file through dlsym() . How to compile using .so file with .c.
3 Answers 3
If libdllname.so is not in the system directory then add its directory to the library path:
g++ -o prog prog.o -L/path/to/my/library/folder -ldllname This is based on your further comments. First guard the declarations of your header file.
#ifndef HEADER_PROTECT #define HEADER_PROTECT ---------- Here is the content of header #endif Next, check in your code, are you defining multiple definitions. Or are you re-defining the standard functions again? Can you please post your code to guide you better? Looks like you have re-defined Close_Comm(), can you check it? Error says that the definition is there in main.c also.
The following is the general way to compile shared object and link it. To compile shared objects.
-g : for debug information fPIC: for position independent code $gcc -fPIC -g myfile The following will create the shared object libmyfile.so $gcc -shared -o libymyfile.so myfile.o Now,In order to link it with your main.c. I assume that the libmyfile.so is in your current path, thus -L./ $gcc main.c -o main.out -L./ -lmyfile Now, you need to export the LD_LIBRARY_PATH on the bash; in order to execute the binary. $LD_LIBRARAY_PATH=$LD_LIBRARAY_PATH:./ $./main.out The dlsym is to load the symbol from the shared object at the run-time. If you want to load the shared object at run time, this can be used. The following is one of the example of dlsym Hack the standard function in library and call the native library function afterwards
How Do so (Shared Object) Filenames Work in Linux
Linux is an open-source operating system that provides users with a wide range of features and functions. One of essential aspects of Linux is use of shared objects (so) files. Shared objects are files that are used by Linux programs to share code and data between different processes. In this article, we will discuss how shared object filenames work in Linux and provide examples to illustrate concepts.
What are Shared Objects (so) Files?
Shared objects are a type of file that contains code and data that can be shared between multiple processes in Linux. They are similar to dynamic link libraries (DLLs) in Windows systems. When a Linux program needs to use a shared object, it loads it into memory and uses code and data contained in file.
Shared objects are used to reduce size of executable files and reduce amount of memory needed to run a program. They also provide a way to share code and data between different programs, allowing for more efficient and modular programming.
How Shared Object Filenames Work
Shared object filenames in Linux follow a specific naming convention that is used to identify file and its contents. filename consists of several parts, each of which provides information about file.
The naming convention for shared object filenames is as follows −
The parts of filename are −
- lib − This is a prefix that indicates that file is a shared library.
- − This is name of library. It is typically a short, descriptive name that identifies purpose of library.
- .so − This is a suffix that indicates that file is a shared object.
- − This is a number that indicates major version of library. A change in major version number indicates a significant change in API or ABI of library.
- − This is a number that indicates minor version of library. A change in minor version number indicates a small change in API or ABI of library.
Examples of Shared Object Filenames
Let’s take a look at some examples of shared object filenames to see how they work.
libcrypto.so.1.1
This filename indicates that file is a shared library called «crypto». major version number is 1, and minor version number is 1. This indicates that this is first major version of library and that there have been some minor changes to API or ABI.
libssl.so.1.1
This filename indicates that file is a shared library called «ssl». major version number is 1, and minor version number is 1. This indicates that this is first major version of library and that there have been some minor changes to API or ABI.
libX11.so.6
This filename indicates that file is a shared library called «X11». major version number is 6, and minor version number is 0. This indicates that this is sixth major version of library and that there have been no minor changes to API or ABI.
libgtk-3.so.0
This filename indicates that file is a shared library called «gtk-3». major version number is 0, and minor version number is 0. This indicates that this is first major version of library and that there have been no minor changes to API or ABI.
How Shared Object Files are Found
Shared objects are searched for and loaded by dynamic linker at runtime. dynamic linker is responsible for resolving symbols and linking shared objects with rest of program.
The dynamic linker searches for shared objects in several directories, including −
- /lib
- /usr
- /usr/local/lib
- Directories listed in LD_LIBRARY_PATH environment variable
When a program is compiled, it includes a list of shared object dependencies that it requires to run. When program is executed, dynamic linker searches for these dependencies in directories listed above. If it finds required shared objects, it loads them into memory and links them with program.
If required shared objects are not found, program will fail to run, and an error message will be displayed. To resolve this issue, you can install missing shared objects or add directory containing missing shared objects to LD_LIBRARY_PATH environment variable.
Benefits of Shared Objects
Shared objects provide several benefits over static libraries, including −
- Reduced memory usage − Shared objects are loaded into memory only when they are needed, reducing amount of memory needed to run a program.
- Dynamic linking − Shared objects allow programs to link with libraries at runtime, enabling them to adapt to changes in environment and load libraries only when they are required.
- Code reusability − Shared objects allow developers to reuse code across different programs, reducing development time and improving code maintainability.
- Faster program startup − Shared objects are loaded only when they are needed, reducing program startup time and improving program performance.
Major vs. Minor Version Numbers
The major and minor version numbers in shared object filenames provide information about compatibility of library with other programs. A change in major version number indicates a significant change in API or ABI of library. Programs that use old version of library may not be compatible with new version.
A change in minor version number indicates a small change in API or ABI of library. Programs that use old version of library should still be compatible with new version, but may not be able to take advantage of new features or improvements in library.
Managing Shared Objects
Managing shared objects in Linux can be challenging, particularly when dealing with dependencies between libraries. Here are some tips for managing shared objects in Linux −
- Use package managers − Most Linux distributions come with package managers that allow you to install and manage shared objects and their dependencies. Using a package manager can help ensure that your system is up-to-date and that you have all necessary dependencies.
- Avoid modifying system directories − Modifying system directories such as /lib and /usr can cause issues with dynamic linker and may break other programs. Instead, install shared objects in directories such as /usr/local/lib or in your home directory.
- Use symbolic links − If you have multiple versions of a shared object, you can use symbolic links to point to current version. This can help ensure that programs that depend on shared object can still find it even if version number changes.
- Check LD_LIBRARY_PATH − If you are experiencing issues with missing shared objects, check LD_LIBRARY_PATH environment variable to ensure that it includes directories containing required shared objects.
Conclusion
Shared objects are an essential part of Linux operating system. They allow programs to share code and data between processes, reducing size of executable files and amount of memory needed to run a program. Shared object filenames in Linux follow a specific naming convention that provides information about file’s contents, including name of library, major and minor version numbers, and file type. dynamic linker searches for shared objects at runtime in several directories, including /lib, /usr, and directories listed in LD_LIBRARY_PATH environment variable. Understanding how shared object filenames work is crucial for developing and running Linux programs efficiently.
Why are .so files executable? [duplicate]
Why do the .so files in /lib have permission 755 and not 644 in Linux? That seems strange According to http://www.gossamer-threads.com/lists/gentoo/user/231943, it seems for old glibc. On my embedded system /lib/libc.so.6 it works even permission is 644.
2 Answers 2
I suspect it’s probably just for historical reasons.
BlueBomber’s answer is probably historically correct, but it’s not actually necessary for shared objects to be executable.
On my Ubuntu system, they aren’t. Of the 30 /lib/*.so* and 600 /usr/lib/*.so* files, only one has execute permissions, and that’s probably just a glitch.
Execute permission permits a file to be executed via one of the exec*() functions; shared object files contain executable code, but they’re not executed in that way.
On the other hand, on a CentOS 5.7 system I have access to, those files are executable; the same is true on a SPARC Solaris 9 system. (It would be interesting to try turning off executable permissions on some of those files to see if it breaks anything, but I’m not able to do so.)
(What Linux distribution are you using?)
This answer to this question shows an example (HP-UX) of a system where the execute bit is actually required. That doesn’t appear to be the case on Linux, where some distributions set the execute bit (probably out of historical inertia) and others don’t. Or maybe some Linuxes actually require it.
Another data point: On my Ubuntu system, I just tried creating my own shared object file. The generated «libfoo.so» file was created with execute permissions, but if I manually chmod -x it, the program that uses it still works.
In any case, setting execute permission on *.so files is Mostly Harmless (and certainly less annoying that, say, setting execute permission on source files).
As fwyzard points out in a comment, some *.so files can actually be executed. For example, on my current system, executing /lib/x86_64-linux-gnu/libc-2.27.so prints version information for the GNU C library. /lib/x86_64-linux-gnu/libpthread-2.27.so behaves similarly.
How to open the files with the extension («.so») [closed]
How to open the files with the extension («.so») like libphpcpp.so and («ELF») format file in editor for editing?
probably with Hex Editor like Bless but if you change the files that are not meant to be changed, then things can happen
2 Answers 2
.so files are «Shared Libraries» (https://en.wikipedia.org/wiki/Library_(computing)#Shared_libraries), they are binary-files meant to be dynamically linked to an executable and as such are unusable on their own.
A Library is a collection of related functions and reusable resources to be used by software applications. Shared-libraries are linked at runtime (dynamic linking) as opposed to compile-time hence their name.
If you want to open a shared-library file, you would open it like any other binary file — with a hex-editor (also called a binary-editor). There are several hex-editors in the standard repositories such as GHex (https://packages.ubuntu.com/xenial/ghex) or Bless (https://packages.ubuntu.com/xenial/bless). The same can be done for ELF executables.
You can install either of them with the following command(s):
But bear in mind though, shared-objects (.so files) are binary files and therefore aren’t meant to be edited manually; you might be able to edit a few strings or values with a hex-editor but you won’t be able to do much since they are unusable on their own.