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Reverted edit by 173.187.199.5 (talk) to last version by Globeplay

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The '''Linear Executable (LE)''' format is a file format for [[executable]]s, [[object code]], and [[Dynamic-link library|DLLs]] designed for 32-bit protected mode operating systems. Originally used by the [[OS/2]] operating system and adopted by various [[DOS extender|DOS extenders]], it also served as the file format for [[VxD|Virtual Device Drivers (VxD)]] in early versions of Windows, including [[Windows 3.x]] and the [[Windows 3.x|Windows 9x]] series.<ref>{{Cite book |last=Sklyarov |first=Dmitry |title=Hidden Keys to Software Break-Ins and Unauthorized |publisher=[[A-LIST]] |year=2004 |isbn=9781931769303 |pages=125}}</ref> The malleability of LE files attracted interest in using them for [[steganography]].{{sfn|Zaidan|Othman|Zaidan|Raji|2009}}

== History ==
The LE format was first introduced in the early 1990s during a period of transition from [[16-bit computing|16-bit]] to [[32-bit computing]]. It was developed as an extension of the older [[New Executable|New Executable (NE)]] format, which was used for 16-bit applications. Limitations in memory management and addressing led to the development of LE as a 32-bit replacement. LE expanded on NE's functionality by allowing the system to operate in protected mode.

An extended version of the format, called LX, was developed specifically for OS/2 Warp and supported further extensions over the LE format.

== Structure ==
Files in the LE format begin with an MZ header (the standard DOS executable header) for backward compatibility with DOS systems. Within the MZ header, at offset <code>0x3C</code>, there is a 32-bit value referred to as the <code>e_lfanew</code>field, which contains a pointer to the extended header (the LE header). The LE header starts with the [[ASCII]] characters <code>LE</code> (or <code>LX</code> in [[OS/2|OS/2 Warp]]). In Linear Executables, file offsets and structures are typically defined relative to the start of the LE header or as absolute offsets within the file.<ref>{{Cite journal |title=IBM OS/2 Warp 4 Toolkit Documents 2 |url=https://archive.org/details/IBMOS2Warp4ToolkitDocuments2/32-bit%20Linear%20eXecutable%20Module%20Format%20%28LX%29%20Specification/ |journal=[[IBM]]}}</ref>

== Usage ==

* [[OS/2]]: IBM's OS/2 operating system used the LE format for its executables and [[Dynamic-link library|DLLs]] in its 32-bit variants.
* [[DOS extender|DOS Extenders]]: The format was popular among DOS extenders, such as [[DOS/4G|DOS/4GW]], which allowed DOS applications to operate in protected mode, bypassing the limitations of real-mode memory constraints.
* [[VxD|Windows VxD Drivers]]: Windows 3.x and the Windows 9x series used the LE format for Virtual Device Drivers (VxD).

==References==
{{Reflist}}

==Sources==
* {{cite book|last=Davis|first=P.|last2=Wallace|first2=M.|title=Windows Undocumented File Formats|publisher=Taylor & Francis|series=File Secrets Revealed|year=1997|isbn=978-0-87930-437-9|chapter-url=https://books.google.com/books?id=eTsXKHqU158C&pg=PA251|access-date=2024-12-17|chapter=LE File Format|pages=251-274}}
* {{cite book |last1=Zaidan |first1=A.A. |last2=Othman |first2=Fazidah |last3=Zaidan |first3=B.B. |last4=Raji |first4=R.Z. |last5=Hasan |first5=Ahmed.K. |last6=Naji |first6=A.W. |title=Proceedings of the World Congress on Engineering |date=2009 |location=London, U.K. |chapter-url=https://www.iaeng.org/publication/WCE2009/WCE2009_pp259-265.pdf |chapter=Securing Cover-File Without Limitation of Hidden Data Size Using Computation Between Cryptography and Steganography|volume=1|isbn=978-988-17012-5-1}}

[[Category:Executable file formats]]

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Linear Executable - Revision history

imported>Jake Wartenberg: Reverted edit by 173.187.199.5 (talk) to last version by Globeplay