I want to know the exact difference between the dll and exe file.
I don't know why everybody is answering this question in context of .NET. The question was a general one and didn't mention .NET anywhere.
Well, the major differences are:
EXE
An exe always runs in its own address space i.e., It is a separate process.
The purpose of an EXE is to launch a separate application of its own.
DLL
A dll always needs a host exe to run. i.e., it can never run in its own address space.
The purpose of a DLL is to have a collection of methods/classes which can be re-used from some other application.
DLL is Microsoft's implementation of a shared library.
The file format of DLL and exe is essentially the same. Windows recognizes the difference between DLL and EXE through PE Header in the file. For details of PE Header, You can have a look at this Article on MSDN
EXE:
It's a executable file
When loading an executable, no export is called, but only the module entry point.
When a system launches new executable, a new process is created
The entry thread is called in context of main thread of that process.
DLL:
It's a Dynamic Link Library
There are multiple exported symbols.
The system loads a DLL into the context of an existing process.
For More Details: http://www.c-sharpcorner.com/Interviews/Answer/Answers.aspxQuestionId=1431&MajorCategoryId=1&MinorCategoryId=1
http://wiki.answers.com/Q/What_is_the_difference_between_an_EXE_and_a_DLL
Reference: http://www.dotnetspider.com/forum/34260-What-difference-between-dll-exe.aspx
The difference is that an EXE has an entry point, a "main" method that will run on execution.
The code within a DLL needs to be called from another application.
There are a few more differences regarding the structure you could mention.
Both DLL and EXE share the same file structure - Portable Executable, or PE. To differentiate between the two, one can look in the Characteristics member of IMAGE_FILE_HEADER inside IMAGE_NT_HEADERS. For a DLL, it has the IMAGE_FILE_DLL (0x2000) flag turned on. For a EXE it's the IMAGE_FILE_EXECUTABLE_IMAGE (0x2) flag.
PE files consist of some headers and a number of sections. There's usually a section for code, a section for data, a section listing imported functions and a section for resources. Some sections may contain more than one thing. The header also describes a list of data directories that are located in the sections. Those data directories are what enables Windows to find what it needs in the PE. But one type of data directory that an EXE will never have (unless you're building a frankenstein EXE) is the export directory. This is where DLL files have a list of functions they export and can be used by other EXE or DLL files. On the other side, each DLL and EXE has an import directory where it lists the functions and DLL files it requires to run.
Also in the PE headers (IMAGE_OPTIONAL_HEADER) is the ImageBase member. It specifies the virtual address at which the PE assumes it will be loaded. If it is loaded at another address, some pointers could point to the wrong memory. As EXE files are amongst the first to be loaded into their new address space, the Windows loader can assure a constant load address and that's usually 0x00400000. That luxury doesn't exist for a DLL. Two DLL files loaded into the same process can request the same address. This is why a DLL has another data directory called Base Relocation Directory that usually resides in its own section - .reloc. This directory contains a list of places in the DLL that need to be rebased/patched so they'll point to the right memory. Most EXE files don't have this directory, but some old compilers do generate them.
You can read more on this topic # MSDN.
This answer was a little more detailed than I thought but read it through.
DLL:
In most cases, a DLL file is a library. There are a couple of types of libraries, dynamic and static - read about the difference. DLL stands for dynamic link library which tells us that it's a part of the program but not the whole thing. It's made of reusable software components (library) which you could use for more than a single program. Bear in mind that it's always possible to use the library source code in many applications using copy-paste, but the idea of a DLL/Static Library is that you could update the code of a library and at the same time update all the applications using it - without compiling.
For example:
Imagine you're creating a Windows GUI component like a Button. In most cases you'd want to re-use the code you've written because it's a complex but a common component - You want many applications to use it but you don't want to give them the source code You can't copy-paste the code for the button in every program, so you decide you want to create a DL-Library (DLL).
This "button" library is required by EXEcutables to run, and without it they will not run because they don't know how to create the button, only how to talk to it.
Likewise, a DLL cannot be executed - run, because it's only a part of the program but doesn't have the information required to create a "process".
EXE:
An executable is the program. It knows how to create a process and how to talk to the DLL. It needs the DLL to create a button, and without it the application doesn't run - ERROR.
hope this helps....
Both DLL and EXE are Portable Executable(PE) Formats
A Dynamic-link library (DLL) is a library and therefore can not be executed directly. If you try to run it you will get an error about a missing entry point. It needs an entry point (main function) to get executed, that entry point can be any application or exe. DLL binding occurs at run-time. That is why its called "Dynamic Link" library.
An Executable (EXE) is a program that can be executed. It has its own entry point. A flag inside the PE header indicates which type of file it is (irrelevant of file extension). The PE header has a field where the entry point for the program resides. In DLLs it isn't used (or at least not as an entry point).
There are many software available to check header information. The only difference causing both to work differently is the bit in header as shown in below diagram.
EXE file has only single main entry means it is isolated application, when a system launches exe, a new process is created while DLLs have many entry points so when application use it no new process started, DLL can be reused and versioned. DLL reduces storage space as different programs can use the same dll.
Dll v/s Exe
1)DLL file is a dynamic link library which can be used in exe files and
other dll files.
EXE file is a executable file which runs in a separate
process which is managed by OS.
2)DLLs are not directly executable . They are separate files containing functions that can be called by programs and other DLLs to perform computations and functions.
An EXE is a program that can be executed . Ex :Windows program
3)Reusability
DLL: They can be reused for some other application. As long as the coder knows the names and parameters of the functions and procedures in the DLL file .
EXE: Only for specific purpose .
4)A DLL would share the same process and memory space of the calling application while an
EXE creates its separate process and memory space.
5)Uses
DLL: You want many applications to use it but you don't want to give them the source code You can't copy-paste the code for the button in every program, so you decide you want to create a DL-Library (DLL).
EXE: When we work with project templates like Windows Forms Applications, Console Applications, WPF Applications and Windows Services they generate an exe assembly when compiled.
6)Similarities :
Both DLL and EXE are binary files have a complex nested structure defined by the Portable Executable format, and they are not intended to be editable by users.
Two things: the extension and the header flag stored in the file.
Both files are PE files. Both contain the exact same layout. A DLL is a library and therefore can not be executed. If you try to run it you'll get an error about a missing entry point. An EXE is a program that can be executed. It has an entry point. A flag inside the PE header indicates which file type it is (irrelevant of file extension). The PE header has a field where the entry point for the program resides. In DLLs it isn't used (or at least not as an entry point).
One minor difference is that in most cases DLLs have an export section where symbols are exported. EXEs should never have an export section since they aren't libraries but nothing prevents that from happening. The Win32 loader doesn't care either way.
Other than that they are identical. So, in summary, EXEs are executable programs while DLLs are libraries loaded into a process and contain some sort of useful functionality like security, database access or something.
The .exe is the program. The .dll is a library that a .exe (or another .dll) may call into.
What sakthivignesh says can be true in that one .exe can use another as if it were a library, and this is done (for example) with some COM components. In this case, the "slave" .exe is a separate program (strictly speaking, a separate process - perhaps running on a separate machine), but one that accepts and handles requests from other programs/components/whatever.
However, if you just pick a random .exe and .dll from a folder in your Program Files, odds are that COM isn't relevant - they are just a program and its dynamically-linked libraries.
Using Win32 APIs, a program can load and use a DLL using the LoadLibrary and GetProcAddress API functions, IIRC. There were similar functions in Win16.
COM is in many ways an evolution of the DLL idea, originally concieved as the basis for OLE2, whereas .NET is the descendant of COM. DLLs have been around since Windows 1, IIRC. They were originally a way of sharing binary code (particularly system APIs) between multiple running programs in order to minimise memory use.
An EXE is visible to the system as a regular Win32 executable. Its entry
point refers to a small loader which initializes the .NET runtime and tells
it to load and execute the assembly contained in the EXE.
A DLL is visible to the system as a Win32 DLL but most likely without any
entry points. The .NET runtime stores information about the contained
assembly in its own header.
dll is a collection of reusable
functions where as an .exe is an
executable which may call these
functions
An exe is an executible program whereas A DLL is a file that can be loaded and executed by programs dynamically.
● .exe and dll are the compiled version of c# code which are also called as
assemblies.
● .exe is a stand alone executable file, which means it can executed directly.
● .dll is a reusable component which cannot be executed directly and it requires
other programs to execute it.
For those looking a concise answer,
If an assembly is compiled as a class library and provides types for other assemblies to use, then it has the ifle extension .dll (dynamic link library), and it cannot be executed standalone.
Likewise, if an assembly is compiled as an application, then it has the file extension .exe (executable) and can be executed standalone. Before .NET Core 3.0, console apps were compiled to .dll fles and had to be executed by the dotnet run command or a host executable. - Source
Difference in DLL and EXE:
1) DLL is an In-Process Component which means running in the same memory space as the client process. EXE is an Out-Process Component which means it runs in its own separate memory space.
2) The DLL contains functions and procedures that other programs can use (promotes reuability) while EXE cannot be shared with other programs.
3) DLL cannot be directly executed as they're designed to be loaded and run by other programs. EXE is a program that is executed directly.
The major exact difference between DLL and EXE that DLL hasn't got an entry point and EXE does. If you are familiar with c++ you can see that build EXE has main() entry function and DLL doesn't :)
Related
When compiling visual studio c# applications PE and EXE files will generate.
So what main difference between PE and EXE file?
As i know PE file contains
PE/COFF Headers,
CLR Headers,
CLR Data,
Meta Data,
IL code,
.data,.text...
than what exe contains?.How PE differ from EXE?
Portable Executables (PE) are files that contain all the necessary information for the operating system to correctly load executable code (.exe, .dll, ...)
This may include dynamic library references for linking, resource management, TLS data, among other things.
Executables (.exe), however, are the files that denote the main execution point on a computer program, that is, speaking in C# terms, the file that contains the Main function or entry point.
.exe files are a subset of PE files, while PE files include .exe, .dll and .ocx files.
So, PEstands for Portable Executable which is the file format for executable binaries in Windows 32bits and 64bits environments.
In my understanding, the information inside the generated PEfile would consist in:
Headers
Metadadata
CLR Data segments
However, the IL Code would be inside the EXE file, since it is supposed to be platform independent and it will be compiled to native code when you run the application (Just-in time-compiler). The PEsection is also in charge of the initialisation of the CLR.
Keep in mind the PE section can be inside the executable file, which make more sense in most applications.
First off I am aware of
1. Is it possible to export a dll definition from my AppDomain?
2. Is it possible to save a dynamic assembly to disk?
3. How can I extract DLL file from memory dump?
but none of those seem to answer my question particularly.
Consider the following scenario: a C# application loads a DLL from a memory stream (so the DLL isn't directly exposed to the user). Is there a tool that explicitly allows dumping or exporting that particular DLL from memory to disk in its original form?
Note: I'd like someone to show me a full step-by-step procedure of extracting an intact DLL from the memory dump of a C# application.
WinDbg with managed debugging extensions is capable of this trick.
First, download WinDbg (google microsoft debugging tools for windows, they are not standalone download, but parts of other kits).
The next part is installing the psscor2 extension (from https://www.microsoft.com/en-us/download/details.aspx?id=1073) and extract it to the folder where WinDbg is located.
Next, run your program and attach WinDbg to it (its in the menu). Type the following commands:
.load psscor2
!SaveAllModules c:\modules\
Find the module you want and enjoy.
I'm loading dynamically a .NET assembly that depends on several bunches of native .dlls
located in various folders. But Windows finds those DLLs only if their folders are in the PATH environment variable when my application is started.
I would like to modify my PATH variable from my program to allow finding the necessary libraries.
According to
MSDN
"the search order is as follows: ...
The directories that are listed in the PATH environment variable."
Which instance of the PATH environment variable is used?
Every process has an instance.
I tried Environment.SetEnvironmentVariable("PATH", ...) but it did not help.
I also tried
SetDefaultDllDirectories()
together with
AddDllDirectory()
but these made no difference either.
The symptom is that when %PATH% contains the necessary folders when starting my .exe
(from a CMD prompt – it is a console application), ProcessMonitor shows that the native .dlls are probed in all the PATH folders, and are eventually found.
But when %PATH% does not contain the necessary folders at the time of starting, then the native .dlls are probed in the .exe folder and in SYSTEM32 only (although %PATH% contains far more),
regardless of the above-mentioned SetEnvironmentVariable()/SetDefaultDllDirectories()/AddDllDirectory() calls.
What is going here? What am I doing wrong? Why I cannot adjust the PATH for my process effectively?
Note: The AppDomain.AssemblyResolve event cannot help me because it's not fired when native .dlls
load other native .dlls.
That is because each process inherits its environment from the process that spawned it. And it didn't occur to the dit at Microsoft that something like PATH might change during the course of execution, so the CLR never refreshes the environment during process execution (and doesn't provide a means for the process to do so itself). See http://social.msdn.microsoft.com/Forums/vstudio/en-US/acf2d0f3-143e-4ba5-acdc-76a70a5c9830/environment-variables-refresh?forum=csharpgeneral for details.
Since the loader is resolving references to unmanaged DLLs via the normal Win32 way, you should probably look at P/Invoking these Win32 functions to alter the DLL search order used by the Win32 LoadLibrary() and LoadLibraryEx():
SetDllDirectory().
Adds a directory to the search path used to locate DLLs for the application.
AddDllDirectory().
Adds a directory to the process DLL search path.
SetDefaultDllDirectories().
Specifies a default set of directories to search when the calling process loads a DLL.
RemoveDllDirectory().
Removes a directory that was added to the process DLL search path by using AddDllDirectory.
See also DLL Search Order.
I'm using mkbundle and trying to create an embedded version of a little program IdaTester that uses Isis2. That system in turn uses features from Mono that depend on MonoPosixHelper
My problem is that mkbundle doesn't recognize the dependency and I end up with an executable that still needs to dynamically link against ~/bin/lib/libMonoPosixHelper.so, causing problems when I move this executable to a system where I don't have Mono installed. In effect, the bundle is missing one of the things it should be statically linked against.
My executable does work, but only if I make sure to run it only on machines that have the dynamic library in the "right place". This defeats the purpose of an embedded executable... I was hoping to be able to hand people this program as a kind of server they could put anywhere and launch as a binary, and obviously if they need to install the library for this to work, the server isn't exactly standalone!
I see how to force mkbundle to include any dll files the program depends upon, but MonoPosixHelper doesn't exist as a dll; this is a Linux-only library and exists only as a shared library. Does anyone know of a way to "force" the bundle to embed it statically?
In case this helps, my little compile script is as follows:
mcs -debug+ IdaTester.cs Isis.cs -r:System.dll -r:Microsoft.CSharp.dll -r:Mono.Posix.dll
mkbundle --static -o IdaTester IdaTester.exe --deps
I then run IdaTester; this works on platforms where the libMonoPosixHelper library can be found, but will fail at runtime when trying to dynamically load that library if running on a platform where libMonoPosixHelper hasn't been installed...
One needs to distribute libMonoPosixHelper.so with the application and change the dll map to make this work.
Background on the problem - Library is Loaded at Runtime
libMonoPosixHelper is not statically linked but searched for and loaded as a P/Invoke call, such as the example below:
[DllImport ("MonoPosixHelper")]
static extern int zipClose (ZipHandle handle, string globalComment);
That is, it is only requested at runtime, not compile time, and so cannot be linked in ahead of time.
Fixing it - Distributing libMonoPosixHelper.so
Four steps are required.
Copy libMonoPosixHelper to the directory you will be distributing the program with.
Update the DllMap config file to avoid a hard coded location.
Embed the config file with mkbundle
Add the path with libMonoPosixHelper.so to the LD_LIBRARY_PATH on the install machine.
To perform each:
1. Copy libMonoPosixHelper to the directory you will be distributing the program with.
libMonoPosixHelper is usually located in the lib folder, simply copy it to the folder you will be making a tarball out of.
cp $MONO_ROOT/lib/libMonoPosixHelper.so ~/MY_PROGRAM/
2. Update the DllMap config file to avoid a hard coded location.
This is the critical bit to avoid the hard coded paths issue. We need to embed a config file with mkbundle that does not specify the path. To do this, first find the mono config file, and also copy that to the local directory
cp $MONO_ROOT/etc/mono/config ~/MY_PROGRAM/config
Now we need to alter this file to remove the specific path for the dll, open it with your favorite editor and change the paths to avoid the specific prefix:
<dllmap dll="MonoPosixHelper" target="MACHINE_SPECIFIC/lib/libMonoPosixHelper.dylib" os="!windows" />
to
<dllmap dll="MonoPosixHelper" target="libMonoPosixHelper.dylib" os="!windows" />
3. Embed the config file with mkbundle
Add the following option to your mkbundle command to embed the newly edited config file:
--config MY_PROGRAM/config
4. Add the path with libMonoPosixHelper.so to the LD_LIBRARY_PATH on the install machine.
Now you can zip up your mkbundled executable, libMonoPosixHelper.so and any other files for distribution. When unzipped and run on a machine, dlopen will now look for libMonoPosixHelper.so just like any other dll. So simply add whatever directory contains your distributed version of libMonoPosixHelper to their LD_LIBRARY_PATH environmental variable
As far as I can tell, the best option available to me is either to build a non-shared Mono library containing the same methods as are currently found in MonoPosixHelper.so, or to provide a copy of MonoPosixHelper.so as a component to be installed in the same folder as my server. Neither seems ideal: the former forces me to "reach into" the Mono distribution, which creates a longer term maintenance issue, while the latter forces me into a more complex distribution and installation mode. But it seems that once one generates a shared library, you simply can't statically link against that version of the library; the Linux loader just doesn't treat such a thing as a library in the way it handles more standard libraries.
In contrast, if I do generate a standard library from the same .o files, the loader will be happy to statically link against it, and because mxbundle ultimately runs cc and hence uses the standard ld, that option would work for me. So I guess that's the answer to my question.
I am using a managed DLL that referencing an unmanaged dll.
I added the unmanaged dll under /External/foo/ directory, and i changed the "Copy To Output Directory" to always.
The problem is that the dlls are copied to the outputDir/External/foo dir and when the runtime tries to find it, it fails with this error: "Unable to load dll: Module cannot be found"
When i copy it directly to the output dir, everything works well.
How can i set the project runtime to search in the sub directories of the outut dir?
Thanks!
You don't want to do this, DLL Search Hell is something you want to avoid. Windows is pretty inflexible about where it looks for DLLs. Rightfully so, DLL Hell is nothing to mess with. The only good place for unmanaged DLLs is in the same directory as your EXE. If you don't want to store the DLLs in the project directory, so copying them is very easy, then you are going to need a post-build event that uses xcopy.exe to copy the DLL to the output directory.
The alternatives are not pretty. If this DLL is implicitly loaded then the only option is to use an installer to add the directory to the system's PATH environment variable. This is a Really Bad idea, way too easy for your program to break. If it is loaded explicitly, either with LoadLibrary or a pinvoke declaration then you have more attractive options since you can alter the search path in your Main() method before the DLL is needed. Either append the path to your local copy of the PATH environment variable by using Environment.SetEnvironmentVariable() or pinvoke SetDllDirectory(). Do beware that you have a deployment problem as well, somebody is going to have to create this subdirectory and copy the DLL there on the user's machine. All great reasons to not do this.
This is something we did in our last project. Write a batch file which copies this unmanaged dll to the output directory. Call the batch file every time the program compiles. You can control the calling of batch file also using a Config key. So it runs based on the config key value true/false. i hope this helps