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Position-independent code

In computing, position-independent code[1] (PIC[1]) or position-independent executable (PIE)[2] is a body of machine code that, being placed somewhere in the primary memory, executes properly regardless of its absolute address. PIC is commonly used for shared libraries, so that the same library code can be loaded at a location in each program's address space where it does not overlap with other memory in use by, for example, other shared libraries. PIC was also used on older computer systems that lacked an MMU,[3] so that the operating system could keep applications away from each other even within the single address space of an MMU-less system.

Position-independent code can be executed at any memory address without modification. This differs from absolute code,[1] which must be loaded at a specific location to function correctly,[1] and load-time locatable (LTL) code,[1] in which a linker or program loader modifies a program before execution, so it can be run only from a particular memory location.[1] Generating position-independent code is often the default behavior for compilers, but they may place restrictions on the use of some language features, such as disallowing use of absolute addresses (position-independent code has to use relative addressing). Instructions that refer directly to specific memory addresses sometimes execute faster, and replacing them with equivalent relative-addressing instructions may result in slightly slower execution, although modern processors make the difference practically negligible.[4]

History edit

In early computers such as the IBM 701[5] (29 April 1952) or the UNIVAC I (31 March 1951) code was not position-independent: each program was built to load into and run from a particular address. Those early computers did not have an operating system and were not multitasking-capable. Programs were loaded into main storage (or even stored on magnetic drum for execution directly from there) and run one at a time. In such an operational context, position-independent code was not necessary.

The IBM System/360 (7 April 1964) was designed with truncated addressing similar to that of the UNIVAC III,[6] with code position independence in mind. In truncated addressing, memory addresses are calculated from a base register and an offset. At the beginning of a program, the programmer must establish addressability by loading a base register; normally, the programmer also informs the assembler with a USING pseudo-op. The programmer can load the base register from a register known to contain the entry point address, typically R15, or can use the BALR (Branch And Link, Register form) instruction (with a R2 Value of 0) to store the next sequential instruction's address into the base register, which was then coded explicitly or implicitly in each instruction that referred to a storage location within the program. Multiple base registers could be used, for code or for data. Such instructions require less memory because they do not have to hold a full 24, 31, 32, or 64 bit address (4 or 8 bytes), but instead a base register number (encoded in 4 bits) and a 12–bit address offset (encoded in 12 bits), requiring only two bytes.

This programming technique is standard on IBM S/360 type systems. It has been in use through to today's IBM System/z. When coding in assembly language, the programmer has to establish addressability for the program as described above and also use other base registers for dynamically allocated storage. Compilers automatically take care of this kind of addressing.

IBM's early operating system DOS/360 (1966) was not using virtual storage (since the early models of System S/360 did not support it), but it did have the ability to place programs to an arbitrary (or automatically chosen) storage location during loading via the PHASE name,* JCL (Job Control Language) statement.

So, on S/360 systems without virtual storage, a program could be loaded at any storage location, but this required a contiguous memory area large enough to hold that program. Sometimes memory fragmentation would occur from loading and unloading differently sized modules. Virtual storage - by design - does not have that limitation.

While DOS/360 and OS/360 did not support PIC, transient SVC routines in OS/360 could not contain relocatable address constants and could run in any of the transient areas without relocation.

Virtual storage was first introduced on IBM System/360 model 67 in (1965) to support IBM's first multi-tasking operating and time-sharing operating system TSS/360. Later versions of DOS/360 (DOS/VS etc.) and later IBM operating systems all utilized virtual storage. Truncated addressing remained as part of the base architecture, and still advantageous when multiple modules must be loaded into the same virtual address space.

By way of comparison, on early segmented systems such as Burroughs MCP on the Burroughs B5000 (1961) and Multics (1964), paging systems such as IBM TSS/360 (1967)[a] or base and bounds[b] systems such as GECOS on the GE 625 and EXEC on the UNIVAC 1107, code was also inherently position-independent, since addresses in a program were relative to the current segment rather than absolute.

The invention of dynamic address translation (the function provided by an MMU) originally reduced the need for position-independent code because every process could have its own independent address space (range of addresses). However, multiple simultaneous jobs using the same code created a waste of physical memory. If two jobs run entirely identical programs, dynamic address translation provides a solution by allowing the system simply to map two different jobs' address 32K to the same bytes of real memory, containing the single copy of the program.

Different programs may share common code. For example, the payroll program and the accounts receivable program may both contain an identical sort subroutine. A shared module (a shared library is a form of shared module) gets loaded once and mapped into the two address spaces.

Technical details edit

Procedure calls inside a shared library are typically made through small procedure linkage table stubs, which then call the definitive function. This notably allows a shared library to inherit certain function calls from previously loaded libraries rather than using its own versions.

Data references from position-independent code are usually made indirectly, through Global Offset Tables (GOTs), which store the addresses of all accessed global variables. There is one GOT per compilation unit or object module, and it is located at a fixed offset from the code (although this offset is not known until the library is linked). When a linker links modules to create a shared library, it merges the GOTs and sets the final offsets in code. It is not necessary to adjust the offsets when loading the shared library later.

Position-independent functions accessing global data start by determining the absolute address of the GOT given their own current program counter value. This often takes the form of a fake function call in order to obtain the return value on stack (x86), in a specific standard register (SPARC, MIPS), or a special register (POWER/PowerPC/Power ISA), which can then be moved to a predefined standard register, or to obtain it into that standard register (PA-RISC, Alpha, ESA/390 and z/Architecture). Some processor architectures, such as the Motorola 68000, Motorola 6809, WDC 65C816, Knuth's MMIX, ARM and x86-64 allow referencing data by offset from the program counter. This is specifically targeted at making position-independent code smaller, less register demanding and hence more efficient.

Windows DLLs edit

Dynamic-link libraries (DLLs) in Microsoft Windows use variant E8 of the CALL instruction (Call near, relative, displacement relative to next instruction). These instructions do not need modification when the DLL is loaded.

Some global variables (e.g. arrays of string literals, virtual function tables) are expected to contain an address of an object in data section respectively in code section of the dynamic library; therefore, the stored address in the global variable must be updated to reflect the address where the DLL was loaded to. The dynamic loader calculates the address referred to by a global variable and stores the value in such global variable; this triggers copy-on-write of a memory page containing such global variable. Pages with code and pages with global variables that do not contain pointers to code or global data remain shared between processes. This operation must be done in any OS that can load a dynamic library at arbitrary address.

In Windows Vista and later versions of Windows, the relocation of DLLs and executables is done by the kernel memory manager, which shares the relocated binaries across multiple processes. Images are always relocated from their preferred base addresses, achieving address space layout randomization (ASLR).[7]

Versions of Windows prior to Vista require that system DLLs be prelinked at non-conflicting fixed addresses at the link time in order to avoid runtime relocation of images. Runtime relocation in these older versions of Windows is performed by the DLL loader within the context of each process, and the resulting relocated portions of each image can no longer be shared between processes.

The handling of DLLs in Windows differs from the earlier OS/2 procedure it derives from. OS/2 presents a third alternative and attempts to load DLLs that are not position-independent into a dedicated "shared arena" in memory, and maps them once they are loaded. All users of the DLL are able to use the same in-memory copy.

Multics edit

In Multics each procedure conceptually[c] has a code segment and a linkage segment. The code segment contains only code and the linkage section serves as a template for a new linkage segment. Pointer register 4 (PR4) points to the linkage segment of the procedure. A call to a procedure saves PR4 in the stack before loading it with a pointer to the callee's linkage segment. The procedure call uses an indirect pointer pair[8] with a flag to cause a trap on the first call so that the dynamic linkage mechanism can add the new procedure and its linkage segment to the Known Segment Table (KST), construct a new linkage segment, put their segment numbers in the caller's linkage section and reset the flag in the indirect pointer pair.

TSS edit

In IBM S/360 Time Sharing System (TSS/360 and TSS/370) each procedure may have a read-only public CSECT and a writable private Prototype Section (PSECT). A caller loads a V-constant for the routine into General Register 15 (GR15) and copies an R-constant for the routine's PSECT into the 19th word of the save area pointed to be GR13.[9]

The Dynamic Loader[10] does not load program pages or resolve address constants until the first page fault.

Position-independent executables edit

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 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 exploits that rely on knowing the offset of the executable code in the binary, such as return-to-libc attacks. (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.)[11]

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?] and non-PIE applications are not rejected.[12][13]

OpenBSD has PIE enabled by default on most architectures since OpenBSD 5.3, released on 1 May 2013.[14] Support for PIE in statically linked binaries, such as the executables in /bin and /sbin directories, was added near the end of 2014.[15] openSUSE added PIE as a default in 2015-02. Beginning with Fedora 23, Fedora maintainers decided to build packages with PIE enabled as the default.[16] Ubuntu 17.10 has PIE enabled by default across all architectures.[17] Gentoo's new profiles now support PIE by default.[18] Around July 2017, Debian enabled PIE by default.[19]

Android enabled support for PIEs in Jelly Bean[20] and removed non-PIE linker support in Lollipop.[21]

See also edit

Notes edit

  1. ^ While TSS/360 supported shared PIC, that was not true of all paging systems
  2. ^ But a separate copy of the code was loaded for each job.
  3. ^ There are some technical deviations for performance reasons that are beyond the scope of this article.

References edit

  1. ^ a b c d e f "Types of Object Code". iRMX 86 Application Loader Reference Manual (PDF). Intel. pp. 1-2, 1-3. Retrieved 2017-08-21. […] Absolute code, and an absolute object module, is code that has been processed by LOC86 to run only at a specific location in memory. The Loader loads an absolute object module only into the specific location the module must occupy. Position-independent code (commonly referred to as PIC) differs from absolute code in that PIC can be loaded into any memory location. The advantage of PIC over absolute code is that PIC does not require you to reserve a specific block of memory. When the Loader loads PIC, it obtains iRMX 86 memory segments from the pool of the calling task's job and loads the PIC into the segments. A restriction concerning PIC is that, as in the PL/M-86 COMPACT model of segmentation […], it can have only one code segment and one data segment, rather than letting the base addresses of these segments, and therefore the segments themselves, vary dynamically. This means that PIC programs are necessarily less than 64K bytes in length. PIC code can be produced by means of the BIND control of LINK86. Load-time locatable code (commonly referred to as LTL code) is the third form of object code. LTL code is similar to PIC in that LTL code can be loaded anywhere in memory. However, when loading LTL code, the Loader changes the base portion of pointers so that the pointers are independent of the initial contents of the registers in the microprocessor. Because of this fixup (adjustment of base addresses), LTL code can be used by tasks having more than one code segment or more than one data segment. This means that LTL programs may be more than 64K bytes in length. FORTRAN 86 and Pascal 86 automatically produce LTL code, even for short programs. LTL code can be produced by means of the BIND control of LINK86. […]
  2. ^ "Position Independent Executables (PIE)".
  3. ^ Levine, John R. (2000) [October 1999]. "Chapter 8: Loading and overlays". Linkers and Loaders. The Morgan Kaufmann Series in Software Engineering and Programming (1 ed.). San Francisco, USA: Morgan Kaufmann. pp. 170–171. ISBN 1-55860-496-0. OCLC 42413382. ISBN 978-1-55860-496-4. Archived from the original on 2012-12-05. Retrieved 2020-01-12. Code: [1][2] Errata: [3]
  4. ^ Gabert, Alexander (January 2004). "Position Independent Code internals". Hardened Gentoo. Retrieved 2009-12-03. […] direct non-PIC-aware addressing is always cheaper (read: faster) than PIC addressing. […]
  5. ^ "701 Announced", IBM, 1952-04-29
  6. ^ Reference Manual UNIVAC III Data Processing System (PDF). Sperry Rand Corporation. 1962. UT-2488.
  7. ^ "Advances in Memory Management for Windows". View.officeapps.live.com. Retrieved 2017-06-23.
  8. ^ "Section 6 Virtual Address Formation", DPS/LEVEL 68 & DPS 8M MULTICS PROCESSOR MANUAL (PDF) (Rev. 1 ed.), Honeywell Information Systems Inc., 1982, pp. 6–21, AL39, retrieved 2023-03-25
  9. ^ "Section 3: TSS for the: Svslcm Programmer". IBM Time Sharing System Concepts and Facilities (PDF) (Seventh ed.). April 1978. p. 61. GC28-2003-6.
  10. ^ IBM System/360 Time Sharing System Dynamic Loader (PDF) (Fourth ed.). September 1971. GY28-2031-3.
  11. ^ Lettieri, G. "Address Space Layout Randomization" (PDF).
  12. ^ "iphone - Non-PIE Binary - The executable 'project name' is not a Position Independent Executable. - Stack Overflow". stackoverflow.com.
  13. ^ "iOS Developer Library". apple.com.
  14. ^ "OpenBSD 5.3 Release". 2013-05-01. Retrieved 2020-05-09.
  15. ^ "Heads Up: Snapshot Upgrades for Static PIE". 2014-12-24. Retrieved 2014-12-24.
  16. ^ "Changes/Harden All Packages - FedoraProject". fedoraproject.org.
  17. ^ "Ubuntu Foundations Team - Weekly Newsletter, 2017-06-15". 2017-06-15. Retrieved 2017-06-17.
  18. ^ "New 17.0 profiles in the Gentoo repository". 2017-11-30. Retrieved 2017-12-10.
  19. ^ Liang, Mudong (2017-08-08). "When did Debian decide to enabled PIE by default?". debian.org. Retrieved 2021-07-06.
  20. ^ "Security Enhancements in Android 1.5 through 4.1  -  Android Open Source Project". Android Open Source Project.
  21. ^ "Security Enhancements in Android 5.0  -  Android Open Source Project". Android Open Source Project.

External links edit

  • Introduction to Position Independent Code
  • Position Independent Code internals
  • The Curious Case of Position Independent Executables

position, independent, code, code, redirects, here, presubscribed, interexchange, carrier, code, carrier, access, code, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsou. PIC code redirects here For presubscribed interexchange carrier code see Carrier access code This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Position independent code news newspapers books scholar JSTOR January 2007 Learn how and when to remove this template message In computing position independent code 1 PIC 1 or position independent executable PIE 2 is a body of machine code that being placed somewhere in the primary memory executes properly regardless of its absolute address PIC is commonly used for shared libraries so that the same library code can be loaded at a location in each program s address space where it does not overlap with other memory in use by for example other shared libraries PIC was also used on older computer systems that lacked an MMU 3 so that the operating system could keep applications away from each other even within the single address space of an MMU less system Position independent code can be executed at any memory address without modification This differs from absolute code 1 which must be loaded at a specific location to function correctly 1 and load time locatable LTL code 1 in which a linker or program loader modifies a program before execution so it can be run only from a particular memory location 1 Generating position independent code is often the default behavior for compilers but they may place restrictions on the use of some language features such as disallowing use of absolute addresses position independent code has to use relative addressing Instructions that refer directly to specific memory addresses sometimes execute faster and replacing them with equivalent relative addressing instructions may result in slightly slower execution although modern processors make the difference practically negligible 4 Contents 1 History 2 Technical details 3 Windows DLLs 4 Multics 5 TSS 6 Position independent executables 7 See also 8 Notes 9 References 10 External linksHistory editIn early computers such as the IBM 701 5 29 April 1952 or the UNIVAC I 31 March 1951 code was not position independent each program was built to load into and run from a particular address Those early computers did not have an operating system and were not multitasking capable Programs were loaded into main storage or even stored on magnetic drum for execution directly from there and run one at a time In such an operational context position independent code was not necessary The IBM System 360 7 April 1964 was designed with truncated addressing similar to that of the UNIVAC III 6 with code position independence in mind In truncated addressing memory addresses are calculated from a base register and an offset At the beginning of a program the programmer must establish addressability by loading a base register normally the programmer also informs the assembler with a USING pseudo op The programmer can load the base register from a register known to contain the entry point address typically R15 or can use the BALR Branch And Link Register form instruction with a R2 Value of 0 to store the next sequential instruction s address into the base register which was then coded explicitly or implicitly in each instruction that referred to a storage location within the program Multiple base registers could be used for code or for data Such instructions require less memory because they do not have to hold a full 24 31 32 or 64 bit address 4 or 8 bytes but instead a base register number encoded in 4 bits and a 12 bit address offset encoded in 12 bits requiring only two bytes This programming technique is standard on IBM S 360 type systems It has been in use through to today s IBM System z When coding in assembly language the programmer has to establish addressability for the program as described above and also use other base registers for dynamically allocated storage Compilers automatically take care of this kind of addressing IBM s early operating system DOS 360 1966 was not using virtual storage since the early models of System S 360 did not support it but it did have the ability to place programs to an arbitrary or automatically chosen storage location during loading via the PHASE name JCL Job Control Language statement So on S 360 systems without virtual storage a program could be loaded at any storage location but this required a contiguous memory area large enough to hold that program Sometimes memory fragmentation would occur from loading and unloading differently sized modules Virtual storage by design does not have that limitation While DOS 360 and OS 360 did not support PIC transient SVC routines in OS 360 could not contain relocatable address constants and could run in any of the transient areas without relocation Virtual storage was first introduced on IBM System 360 model 67 in 1965 to support IBM s first multi tasking operating and time sharing operating system TSS 360 Later versions of DOS 360 DOS VS etc and later IBM operating systems all utilized virtual storage Truncated addressing remained as part of the base architecture and still advantageous when multiple modules must be loaded into the same virtual address space By way of comparison on early segmented systems such as Burroughs MCP on the Burroughs B5000 1961 and Multics 1964 paging systems such as IBM TSS 360 1967 a or base and bounds b systems such as GECOS on the GE 625 and EXEC on the UNIVAC 1107 code was also inherently position independent since addresses in a program were relative to the current segment rather than absolute The invention of dynamic address translation the function provided by an MMU originally reduced the need for position independent code because every process could have its own independent address space range of addresses However multiple simultaneous jobs using the same code created a waste of physical memory If two jobs run entirely identical programs dynamic address translation provides a solution by allowing the system simply to map two different jobs address 32K to the same bytes of real memory containing the single copy of the program Different programs may share common code For example the payroll program and the accounts receivable program may both contain an identical sort subroutine A shared module a shared library is a form of shared module gets loaded once and mapped into the two address spaces Technical details editProcedure calls inside a shared library are typically made through small procedure linkage table stubs which then call the definitive function This notably allows a shared library to inherit certain function calls from previously loaded libraries rather than using its own versions Data references from position independent code are usually made indirectly through Global Offset Tables GOTs which store the addresses of all accessed global variables There is one GOT per compilation unit or object module and it is located at a fixed offset from the code although this offset is not known until the library is linked When a linker links modules to create a shared library it merges the GOTs and sets the final offsets in code It is not necessary to adjust the offsets when loading the shared library later Position independent functions accessing global data start by determining the absolute address of the GOT given their own current program counter value This often takes the form of a fake function call in order to obtain the return value on stack x86 in a specific standard register SPARC MIPS or a special register POWER PowerPC Power ISA which can then be moved to a predefined standard register or to obtain it into that standard register PA RISC Alpha ESA 390 and z Architecture Some processor architectures such as the Motorola 68000 Motorola 6809 WDC 65C816 Knuth s MMIX ARM and x86 64 allow referencing data by offset from the program counter This is specifically targeted at making position independent code smaller less register demanding and hence more efficient Windows DLLs editMain article Dynamic link library This section needs additional citations for verification Please help improve this article by adding citations to reliable sources in this section Unsourced material may be challenged and removed April 2018 Learn how and when to remove this template message Dynamic link libraries DLLs in Microsoft Windows use variant E8 of the CALL instruction Call near relative displacement relative to next instruction These instructions do not need modification when the DLL is loaded Some global variables e g arrays of string literals virtual function tables are expected to contain an address of an object in data section respectively in code section of the dynamic library therefore the stored address in the global variable must be updated to reflect the address where the DLL was loaded to The dynamic loader calculates the address referred to by a global variable and stores the value in such global variable this triggers copy on write of a memory page containing such global variable Pages with code and pages with global variables that do not contain pointers to code or global data remain shared between processes This operation must be done in any OS that can load a dynamic library at arbitrary address In Windows Vista and later versions of Windows the relocation of DLLs and executables is done by the kernel memory manager which shares the relocated binaries across multiple processes Images are always relocated from their preferred base addresses achieving address space layout randomization ASLR 7 Versions of Windows prior to Vista require that system DLLs be prelinked at non conflicting fixed addresses at the link time in order to avoid runtime relocation of images Runtime relocation in these older versions of Windows is performed by the DLL loader within the context of each process and the resulting relocated portions of each image can no longer be shared between processes The handling of DLLs in Windows differs from the earlier OS 2 procedure it derives from OS 2 presents a third alternative and attempts to load DLLs that are not position independent into a dedicated shared arena in memory and maps them once they are loaded All users of the DLL are able to use the same in memory copy Multics editIn Multics each procedure conceptually c has a code segment and a linkage segment The code segment contains only code and the linkage section serves as a template for a new linkage segment Pointer register 4 PR4 points to the linkage segment of the procedure A call to a procedure saves PR4 in the stack before loading it with a pointer to the callee s linkage segment The procedure call uses an indirect pointer pair 8 with a flag to cause a trap on the first call so that the dynamic linkage mechanism can add the new procedure and its linkage segment to the Known Segment Table KST construct a new linkage segment put their segment numbers in the caller s linkage section and reset the flag in the indirect pointer pair TSS editIn IBM S 360 Time Sharing System TSS 360 and TSS 370 each procedure may have a read only public CSECT and a writable private Prototype Section PSECT A caller loads a V constant for the routine into General Register 15 GR15 and copies an R constant for the routine s PSECT into the 19th word of the save area pointed to be GR13 9 The Dynamic Loader 10 does not load program pages or resolve address constants until the first page fault Position independent executables editSee 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 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 exploits that rely on knowing the offset of the executable code in the binary such as return to libc attacks 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 11 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 and non PIE applications are not rejected 12 13 OpenBSD has PIE enabled by default on most architectures since OpenBSD 5 3 released on 1 May 2013 14 Support for PIE in statically linked binaries such as the executables in a href bin html class mw redirect title bin bin a and sbin directories was added near the end of 2014 15 openSUSE added PIE as a default in 2015 02 Beginning with Fedora 23 Fedora maintainers decided to build packages with PIE enabled as the default 16 Ubuntu 17 10 has PIE enabled by default across all architectures 17 Gentoo s new profiles now support PIE by default 18 Around July 2017 Debian enabled PIE by default 19 Android enabled support for PIEs in Jelly Bean 20 and removed non PIE linker support in Lollipop 21 See also edit nbsp Computer programming portalDynamic linker Object file Code segmentNotes edit While TSS 360 supported shared PIC that was not true of all paging systems But a separate copy of the code was loaded for each job There are some technical deviations for performance reasons that are beyond the scope of this article References edit a b c d e f Types of Object Code iRMX 86 Application Loader Reference Manual PDF Intel pp 1 2 1 3 Retrieved 2017 08 21 Absolute code and an absolute object module is code that has been processed by LOC86 to run only at a specific location in memory The Loader loads an absolute object module only into the specific location the module must occupy Position independent code commonly referred to as PIC differs from absolute code in that PIC can be loaded into any memory location The advantage of PIC over absolute code is that PIC does not require you to reserve a specific block of memory When the Loader loads PIC it obtains iRMX 86 memory segments from the pool of the calling task s job and loads the PIC into the segments A restriction concerning PIC is that as in the PL M 86 COMPACT model of segmentation it can have only one code segment and one data segment rather than letting the base addresses of these segments and therefore the segments themselves vary dynamically This means that PIC programs are necessarily less than 64K bytes in length PIC code can be produced by means of the BIND control of LINK86 Load time locatable code commonly referred to as LTL code is the third form of object code LTL code is similar to PIC in that LTL code can be loaded anywhere in memory However when loading LTL code the Loader changes the base portion of pointers so that the pointers are independent of the initial contents of the registers in the microprocessor Because of this fixup adjustment of base addresses LTL code can be used by tasks having more than one code segment or more than one data segment This means that LTL programs may be more than 64K bytes in length FORTRAN 86 and Pascal 86 automatically produce LTL code even for short programs LTL code can be produced by means of the BIND control of LINK86 Position Independent Executables PIE Levine John R 2000 October 1999 Chapter 8 Loading and overlays Linkers and Loaders The Morgan Kaufmann Series in Software Engineering and Programming 1 ed San Francisco USA Morgan Kaufmann pp 170 171 ISBN 1 55860 496 0 OCLC 42413382 ISBN 978 1 55860 496 4 Archived from the original on 2012 12 05 Retrieved 2020 01 12 Code 1 2 Errata 3 Gabert Alexander January 2004 Position Independent Code internals Hardened Gentoo Retrieved 2009 12 03 direct non PIC aware addressing is always cheaper read faster than PIC addressing 701 Announced IBM 1952 04 29 Reference Manual UNIVAC III Data Processing System PDF Sperry Rand Corporation 1962 UT 2488 Advances in Memory Management for Windows View officeapps live com Retrieved 2017 06 23 Section 6 Virtual Address Formation DPS LEVEL 68 amp DPS 8M MULTICS PROCESSOR MANUAL PDF Rev 1 ed Honeywell Information Systems Inc 1982 pp 6 21 AL39 retrieved 2023 03 25 Section 3 TSS for the Svslcm Programmer IBM Time Sharing System Concepts and Facilities PDF Seventh ed April 1978 p 61 GC28 2003 6 IBM System 360 Time Sharing System Dynamic Loader PDF Fourth ed September 1971 GY28 2031 3 Lettieri G Address Space Layout Randomization PDF iphone Non PIE Binary The executable project name is not a Position Independent Executable Stack Overflow stackoverflow com iOS Developer Library apple com OpenBSD 5 3 Release 2013 05 01 Retrieved 2020 05 09 Heads Up Snapshot Upgrades for Static PIE 2014 12 24 Retrieved 2014 12 24 Changes Harden All Packages FedoraProject fedoraproject org Ubuntu Foundations Team Weekly Newsletter 2017 06 15 2017 06 15 Retrieved 2017 06 17 New 17 0 profiles in the Gentoo repository 2017 11 30 Retrieved 2017 12 10 Liang Mudong 2017 08 08 When did Debian decide to enabled PIE by default debian org Retrieved 2021 07 06 Security Enhancements in Android 1 5 through 4 1 Android Open Source Project Android Open Source Project Security Enhancements in Android 5 0 Android Open Source Project Android Open Source Project External links editIntroduction to Position Independent Code Position Independent Code internals Programming in Assembly Language with PIC The Curious Case of Position Independent Executables Retrieved from https en wikipedia org w index php title Position independent code amp oldid 1164854994 PIE, wikipedia, wiki, book, books, library,

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