Static pie binaries
In computingposition-independent code  PIC  or position-independent executable PIE is a body of machine code that, being placed somewhere in the primary memoryexecutes properly regardless of its absolute address.
PIC is commonly used for shared librariesso that the same library code can be loaded in a location in each program address space where it will not overlap any other uses of memory for example, other shared libraries. PIC was also used on older computer systems lacking an MMUstatic pie binaries 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 which must be loaded at a specific location to function correctly,  and load-time locatable LTL code,  in which a linker or program loader modifies a program before execution so it can be run only from a particular memory location.
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. Where a multitasking operating system allowed multiple jobs to be static pie binaries using separate programs at the static pie binaries time, operations had to be scheduled such that no two concurrent jobs would run programs that required static pie binaries same load addresses.
For example, both a payroll program and an accounts receivable program built to run at address 32K could not both be run at the same time. Sometimes multiple versions of a program were maintained, each built for a different load address.
A special class of programs, called self-relocating programs, were coded to relocate themselves after loading. Only one copy of the program was required, but once loaded the static pie binaries could not static pie binaries moved. By way of comparison, on early segmented or base and bounds static pie binaries such as Burroughs B and Multicscode was inherently position-independent, since addresses in a program were relative to the current segment rather than absolute.
Position-independent static pie binaries was developed to eliminate these restrictions for non-segmented systems. A position-independent program could be loaded at any address in memory.
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 static pie binaries 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.
Static pie binaries 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 static pie binaries form of shared module gets loaded once and mapped static pie binaries the two address spaces.
Procedure calls inside a shared library are typically made through small procedure linkage table static pie binarieswhich 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 GOTswhich 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 static pie binaries counter value.
This is specifically targeted at making position-independent code smaller, less register demanding and hence more efficient. These instructions do not need to static pie binaries fixed up when a DLL is loaded.
Some global variables e. 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 static pie binaries memory page static pie binaries 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 needs to 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 static pie binaries 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. Versions of Windows prior to Vista require system DLLs to 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. All users of the DLL are able to use the same in-memory copy. 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. Static pie binaries binaries are used static pie binaries some security-focused Linux distributions to allow PaX or Exec Shield to use address space layout randomization 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.
Gentoo 's new profiles now support PIE by default. From Static pie binaries, the free encyclopedia. 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.
January Learn how and when to remove this template message. This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Address space layout randomization. Computer programming portal Information technology portal. The Loader loads static pie binaries 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 static pie binaries be loaded into any memory location.
This means that PIC programs are necessarily less than 64K bytes in length. Load-time locatable code commonly referred to as LTL code is the third form of object code. 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 addressesLTL 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. Archived from the original on Android Open Source Project. Application binary interface ABI. Binary code compatibility Foreign function interface Language binding Linker dynamic Loader Year problem. Retrieved from " https: Operating system technology Computer libraries Computer file formats.
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