Editing Position-independent code (section)

== {{Anchor|PIE}}Position-independent executables ==
{{See also|Address space layout randomization}}
''Position-independent executables'' (PIE) are executable binaries made entirely from position-independent code. While some systems only run PIC executables, there are other reasons they are used. PIE binaries are used in some [[Security-focused operating system|security-focused]] [[Linux]] distributions to allow [[PaX]] or [[Exec Shield]] to use [[address space layout randomization]] (ASLR) to prevent attackers from knowing where existing executable code is during a security attack using [[security exploit|exploits]] that rely on knowing the offset of the executable code in the binary, such as [[return-to-libc attack]]s. (The official Linux kernel since 2.6.12 of 2005 has a weaker ASLR that also works with PIE. It is weak in that randomness is applied to whole ELF file units.)<ref>{{cite web |last1=Lettieri |first1=G |title=Address Space Layout Randomization |url=https://lettieri.iet.unipi.it/hacking/aslr-pie.pdf}}</ref>

Apple's [[macOS]] and [[iOS]] fully support PIE executables as of versions 10.7 and 4.3, respectively; a warning is issued when non-PIE iOS executables are submitted for approval to Apple's App Store but there's no hard requirement yet {{when|date=July 2020}} and non-PIE applications are not rejected.<ref name="Non-PIE"/><ref name="iOS"/>

[[OpenBSD]] has PIE enabled by default on most architectures since OpenBSD 5.3, released on 1 May 2013.<ref name="OpenBSD_2013"/>  Support for PIE in [[statically linked]] binaries, such as the executables in <code>[[/bin]]</code> and <code>/sbin</code> directories, was added near the end of 2014.<ref name="Fedora_2014"/> openSUSE added PIE as a default in 2015-02. Beginning with [[Fedora (operating system)|Fedora]]&nbsp;23, Fedora maintainers decided to build packages with PIE enabled as the default.<ref name="Fedora"/> [[Ubuntu (operating system)|Ubuntu]] [[Ubuntu version history#Ubuntu 17.10 (Artful Aardvark)|17.10]] has PIE enabled by default across all architectures.<ref name="Ubuntu"/> [[Gentoo Linux|Gentoo]]'s new profiles now support PIE by default.<ref name="gentoo-pie"/> Around July 2017, [[Debian]] enabled PIE by default.<ref name="Liang_2017"/>

[[Android (operating system)|Android]] enabled support for PIEs in [[Android Jelly Bean|Jelly Bean]]<ref name="Android_1-4"/> and removed non-PIE linker support in [[Android Lollipop|Lollipop]].<ref name="Android_5"/>