View source for Portable Executable

{{short description|File format}}
{{Infobox file format
| name = Portable Executable
| icon = 
| extension = <code>.acm</code>, <code>.ax</code>, <code>.cpl</code>, <code>.dll</code>, <code>.drv</code>, <code>.efi</code>, <code>.exe</code>, <code>.mui</code>, <code>.ocx</code>, <code>.scr</code>, <code>.sys</code>, <code>.tsp</code>, <code>.mun</code>
| mime = application/vnd.microsoft.portable-executable<ref>{{Cite web|url=https://www.iana.org/assignments/media-types/application/vnd.microsoft.portable-executable|title=application/vnd.microsoft.portable-executable|access-date=2017-03-26|last=Andersson|first=Henrik|date=2015-04-23|publisher=IANA}}</ref>
| owner = Currently: [[Company:Microsoft|Microsoft]]
| genre = [[Binary file|Binary]], [[Executable|executable]], [[Object code|object]], shared libraries
| extendedfrom = [[DOS MZ executable]]<br/>[[COFF]]
| containerfor = 
| containedby = 
|= 
}}
The '''Portable Executable''' ('''PE''') format is a [[File format|file format]] for [[Executable|executable]]s, [[Object file|object code]], [[Dynamic-link library|DLL]]s and others used in 32-bit and 64-bit versions of [[Software:Microsoft Windows|Windows]] [[Operating system|operating system]]s, and in UEFI environments.<ref>{{Cite web |title=Portable executable (PE) - Definition - Trend Micro IN |url=https://www.trendmicro.com/vinfo/in/security/definition/portable-executable-pe |access-date=2022-11-10 |website=www.trendmicro.com}}</ref> The PE format is a data structure that encapsulates the information necessary for the Windows OS loader to manage the wrapped [[Executable|executable code]]. This includes dynamic library references for linking, [[Application programming interface|API]] export and import tables, resource management data and [[Thread-local storage|thread-local storage]] (TLS) data. On [[Software:Windows NT|NT]] operating systems, the PE format is used for EXE, [[Dynamic-link library|DLL]], SYS ([[Device driver|device driver]]), MUI and other file types. The Unified Extensible Firmware Interface (UEFI) specification states that PE is the standard executable format in EFI environments.<ref>{{cite web|url=https://uefi.org/sites/default/files/resources/UEFI%20Spec%202.8B%20May%202020.pdf|title=UEFI Specification, version 2.8B}}, a note on p.15, states that "this image type is chosen to enable UEFI images to contain Thumb and Thumb2 instructions while defining the EFI interfaces themselves to be in ARM mode."</ref>

On Windows NT operating systems, PE currently supports the x86-32, [[X86-64|x86-64]] (AMD64/Intel 64), [[Engineering:IA-64|IA-64]], [[ARM architecture|ARM]] and ARM64 [[Instruction set architecture|instruction set architecture]]s (ISAs). Prior to [[Software:Windows 2000|Windows 2000]], Windows NT (and thus PE) supported the [[MIPS architecture|MIPS]], [[DEC Alpha|Alpha]], and [[PowerPC]] ISAs. Because PE is used on [[Software:Windows CE|Windows CE]], it continues to support several variants of the MIPS, [[ARM architecture|ARM]] (including [[ARM architecture#Thumb|Thumb]]), and [[Engineering:SuperH|SuperH]] ISAs.<ref name="PE Format (Windows)">{{cite web|url=https://msdn.microsoft.com/en-us/library/windows/desktop/ms680547(v=vs.85).aspx|title=PE Format (Windows)| access-date=2017-10-21}}</ref>

Analogous formats to PE are [[Executable and Linkable Format|ELF]] (used in [[Software:Linux|Linux]] and most other versions of [[Software:Unix|Unix]]) and [[Mach-O]] (used in [[Software:MacOS|macOS]] and [[Software:IOS|iOS]]).

== History ==

Microsoft migrated to the PE format from the 16-bit [[New Executable|NE]] formats with the introduction of the [[Software:Windows NT 3.1|Windows NT 3.1]] operating system. All later versions of Windows, including Windows 95/98/ME and the [[Software:Win32s|Win32s]] addition to Windows 3.1x, support the file structure. The format has retained limited legacy support to bridge the gap between [[Engineering:DOS|DOS]]-based and NT systems. For example, PE/COFF headers still include a [[DOS MZ executable|DOS executable program]], which is by default a DOS stub that displays a message like "This program cannot be run in DOS mode" (or similar), though it can be a full-fledged DOS version of the program (a later notable case being the Windows 98 SE installer).<ref>E.g. Microsoft's linker has [http://msdn.microsoft.com/en-us/library/7z0585h5.aspx /STUB switch] to attach one</ref> This constitutes a form of [[Fat binary|fat binary]]. PE also continues to serve the changing Windows platform. Some extensions include the .NET PE format (see below), a version with 64-bit address space support called PE32+,<ref>In order to know whether the executable code is 32- or 64-bit, check the Machine field in the IMAGE_FILE_HEADER. ([https://gdatasoftware.com/blog/pebitnesstrick PE trick explained: Telling 32 and 64 bit apart with naked eye] by Karsten Hahn)<br>To see if addresses in the executable are 32- or 64-bit, check the Magic field in the IMAGE_OPTIONAL_HEADER. 10B<sub>16</sub> indicates a PE32 file, whereas 20B<sub>16</sub> indicates a PE32+ file. ([https://docs.microsoft.com/en-us/windows/win32/debug/pe-format PE Format] at Microsoft.com)</ref> and a specification for Windows CE.

==Technical details==

===Layout===
[[File:Portable Executable 32 bit Structure in SVG fixed.svg|thumb|Structure of a Portable Executable 32 bit]]
A PE file consists of a number of headers and sections that tell the [[Dynamic linker|dynamic linker]] how to map the file into memory. An executable image consists of several different regions, each of which requires different memory protection; so the start of each section must be aligned to a page boundary.<ref>{{cite web |url=http://www.csn.ul.ie/%7Ecaolan/pub/winresdump/winresdump/doc/pefile2.html |title=The Portable Executable File From Top to Bottom |access-date=2017-10-21}}</ref> For instance, typically the ''.text'' section (which holds program code) is mapped as execute/read-only, and the ''.data'' section (holding global variables) is mapped as no-execute/read write. However, to avoid wasting space, the different sections are not page aligned on disk. Part of the job of the dynamic linker is to map each section to memory  individually and assign the correct permissions to the resulting regions, according to the instructions found in the headers.<ref name="Peering Inside">{{cite web |url=https://msdn.microsoft.com/en-us/library/ms809762.aspx |title=Peering Inside the PE: A Tour of the Win32 Portable Executable File |access-date=2017-10-21}}</ref>

===Import table===
One section of note is the ''import address table'' (IAT), which is used as a lookup table when the application is calling a function in a different module. It can be in the form of both [[Dynamic-link library#Symbol resolution and binding|import by ordinal and import by name]]. Because a compiled program cannot know the memory location of the libraries it depends upon, an indirect jump is required whenever an API call is made.  As the dynamic linker loads modules and joins them together, it writes actual addresses into the IAT slots, so that they point to the memory locations of the corresponding library functions.  Though this adds an extra jump over the cost of an intra-module call resulting in a performance penalty, it provides a key benefit: The number of memory pages that need to be [[Copy-on-write|copy-on-write]] changed by the loader is minimized, saving memory and disk I/O time. If the compiler knows ahead of time that a call will be inter-module (via a dllimport attribute) it can produce more optimized code that simply results in an indirect call [[Opcode|opcode]].<ref name="Peering Inside" />

===Relocations===
PE files normally do not contain [[Position-independent code|position-independent code]]. Instead they are compiled to a preferred ''[[Base address|base address]]'', and all addresses emitted by the compiler/linker are fixed ahead of time. If a PE file cannot be loaded at its preferred address (because it's already taken by something else), the operating system will ''[[Rebasing|rebase]]'' it. This involves recalculating every absolute address and modifying the code to use the new values. The loader does this by comparing the preferred and actual load addresses, and calculating a [[Delta encoding|delta]] value. This is then added to the preferred address to come up with the new address of the memory location.  Base [[Relocation (computing)|relocation]]s are stored in a list and added, as needed, to an existing memory location. The resulting code is now private to the process and no longer [[Shared library|shareable]], so many of the memory saving benefits of DLLs are lost in this scenario. It also slows down loading of the module significantly. For this reason rebasing is to be avoided wherever possible, and the DLLs shipped by Microsoft have base addresses pre-computed so as not to overlap. In the no rebase case PE therefore has the advantage of very efficient code, but in the presence of rebasing the memory usage hit can be expensive. This contrasts with [[Executable and Linkable Format|ELF]] where fully position-independent code is usually preferred to load-time relocation, thus trading off execution time in favor of lower memory usage.

==.NET, metadata, and the PE format==
In a .NET executable, the PE code section contains a stub that invokes the [[Common Language Runtime|CLR]] virtual machine startup entry, <code>_CorExeMain</code> or <code>_CorDllMain</code> in <code>mscoree.dll</code>, much like it was in [[Visual Basic]] executables. The virtual machine then makes use of .NET metadata present, the root of which, <code>IMAGE_COR20_HEADER</code> (also called "CLR header") is pointed to by <code>IMAGE_DIRECTORY_ENTRY_COMHEADER</code><ref>The entry was previously used for COM+ metadata in COM+ applications, hence the name</ref> entry in the PE header's data directory. <code>IMAGE_COR20_HEADER</code> strongly resembles PE's optional header, essentially playing its role for the CLR loader.<ref name="PE Format (Windows)"/>

The CLR-related data, including the root structure itself, is typically contained in the common code section, <code>.text</code>. It is composed of a few directories: metadata, embedded resources, strong names and a few for native-code interoperability. Metadata directory is a set of tables that list all the distinct .NET entities in the assembly, including types, methods, fields, constants, events, as well as references between them and to other assemblies.

==Use on other operating systems==
The PE format is also used by [[Software:ReactOS|ReactOS]], as ReactOS is intended to be [[Binary-code compatibility|binary-compatible]] with Windows.  It has also historically been used by a number of other operating systems, including [[Software:SkyOS|SkyOS]] and [[Software:BeOS|BeOS]] R3. However, both SkyOS and BeOS eventually moved to [[Executable and Linkable Format|ELF]].{{citation needed|date=March 2021}}

As the [[Software:Mono|Mono development platform]] intends to be binary compatible with the Microsoft .NET Framework, it uses the same PE format as the Microsoft implementation. The same goes for Microsoft's own cross-platform .NET Core.

On [[X86|x86]](-64) [[Unix-like]] operating systems, Windows binaries (in PE format) can be executed with [[Software:Wine|Wine]]. The HX DOS Extender also uses the PE format for native DOS 32-bit binaries, plus it can, to some degree, execute existing Windows binaries in DOS, thus acting like an equivalent of Wine for DOS.

On [[IA-32]] and [[X86-64|x86-64]] [[Software:Linux|Linux]] one can also run [[Software:Microsoft Windows|Windows]]' [[Dynamic-link library|DLLs]] under load library.<ref>{{Cite web|url=https://github.com/taviso/loadlibrary|title = GitHub - taviso/Loadlibrary: Porting Windows Dynamic Link Libraries to Linux|website=[[GitHub]]}}</ref>

Mac OS X 10.5 has the ability to load and parse PE files, but is not binary compatible with Windows.<ref name="chartier">{{cite web|last=Chartier |first=David |title=Uncovered: Evidence that Mac OS X could run Windows apps soon |work=Ars Technica |url=https://arstechnica.com/journals/apple.ars/2007/11/30/uncovered-evidence-that-mac-os-x-could-run-windows-apps-soon |date=2007-11-30 |access-date=2007-12-03 |quote=...&nbsp;Steven Edwards describes the discovery that Leopard apparently contains an undocumented loader for Portable Executables, a type of file used in 32-bit and 64-bit versions of Windows. More poking around revealed that Leopard's own loader tries to find Windows DLL files when attempting to load a Windows binary. }}</ref>

UEFI and EFI firmware use Portable Executable files as well as the Windows ABI x64 [[Calling convention|calling convention]] for applications.

==See also==
* [[A.out|a.out]]
* [[Comparison of executable file formats]]
* Executable compression
* [[Software:Ar (Unix)|ar (Unix)]] since all COFF libraries use that same format
* [[Software:Application virtualization|Application virtualization]]

==References==
{{reflist}}

==External links==
*[https://docs.microsoft.com/en-us/windows/desktop/Debug/pe-format PE Format]  (latest online document)
*[https://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/pecoff.docx Microsoft Portable Executable and Common Object File Format Specification] (revision 11.0, .docx format, Jan 2017)
*[https://bytepointer.com/download.php?name=pecoff_v10.docx Microsoft Portable Executable and Common Object File Format Specification] (revision 10.0, .docx format, Jun 2016)
*[https://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/pecoff_v83.docx Microsoft Portable Executable and Common Object File Format Specification] (revision 8.3, .docx format, Feb 2013)
*[https://web.archive.org/web/20100923032233/http://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/pecoff_v8.docx Microsoft Portable Executable and Common Object File Format Specification] (revision 8.2, .docx format, Sep 2010)
*[https://web.archive.org/web/20081211013825/http://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/pecoff_v8.docx Microsoft Portable Executable and Common Object File Format Specification] (revision 8.1, .docx format, Feb 2008)
*[https://web.archive.org/web/20060706172855/http://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/pecoff_v8.doc Microsoft Portable Executable and Common Object File Format Specification] (revision 8.0, .doc format, May 2006)
*[https://web.archive.org/web/20030724131335/http://www.microsoft.com/whdc/hwdev/download/hardware/pecoff.doc Microsoft Portable Executable and Common Object File Format Specification] (revision 6.0, .doc format, Feb 1999)
*[https://bytepointer.com/resources/pecoff_v5.0.htm Microsoft Portable Executable and Common Object File Format Specification] (revision 5.0, .html format, Oct 1997)
*[https://bytepointer.com/resources/pecoff_v4.1.htm Microsoft Portable Executable and Common Object File Format Specification] (revision 4.1, .html format, Aug 1994)
*[https://bytepointer.com/resources/pecoff_v4.0.htm Microsoft Portable Executable and Common Object File Format Specification] (revision 4.0, .html format, Sep 1993)
*[https://openwatcom.org/ftp/devel/docs/pe_and_symbols.pdf Tool Interface Standard (TIS) Formats Specifications for Windows Version 1.0] (Intel Order Number 241597, TIS Committee, Feb 1993)
*[https://bytepointer.com/resources/oleary_pe_format.htm Portable Executable Format] (Micheal J. O'Leary, Microsoft Developer Support)
*[https://learn.microsoft.com/en-us/previous-versions/ms809762(v=msdn.10) Peering Inside the PE: A Tour of the Win32 Portable Executable File Format] (archived from [https://web.archive.org/web/20080907145154/http://msdn.microsoft.com/en-us/magazine/ms809762.aspx the original]) by Matt Pietrek (Microsoft Systems Journal, March 1994)
*[https://learn.microsoft.com/en-us/archive/msdn-magazine/2002/february/inside-windows-win32-portable-executable-file-format-in-detail Part I. An In-Depth Look into the Win32 Portable Executable File Format] (archived from [https://web.archive.org/web/20021105233944/http://msdn.microsoft.com/msdnmag/issues/02/02/PE/default.aspx the original]) by Matt Pietrek (MSDN Magazine, February 2002)
*[https://learn.microsoft.com/en-us/archive/msdn-magazine/2002/march/inside-windows-an-in-depth-look-into-the-win32-portable-executable-file-format-part-2 Part II. An In-Depth Look into the Win32 Portable Executable File Format] (archived from [https://web.archive.org/web/20021105025618/http://msdn.microsoft.com/msdnmag/issues/02/03/PE2/default.aspx the original] by Matt Pietrek (MSDN Magazine, March 2002)
*[https://archive.today/20130130042959/http://www.ntcore.com/files/dotnetformat.htm The .NET File Format by Daniel Pistelli]
*[http://blog.dkbza.org/ Ero Carrera's blog describing the PE header and how to walk through]
*[http://www.andreybazhan.com/pe-internals/ PE Internals provides an easy way to learn the Portable Executable File Format]
* [http://www.pe-explorer.com/ PE Explorer]
{{Executables}}

[[Category:Executable file formats]]
[[Category:Windows administration]]

{{Sourceattribution|Portable Executable}}