Difference between revisions of "Relocatable binary"

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Larger programs are [[compiler|compiled]] or [[assembler|assembled]] from a series of smaller modules of [[source code]], producing '''relocatable binary''' modules of the low-level binary 'understood' by a given [[CPU]], which are then '''linked''' together to produce an [[object code|executable binary]] object.
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Larger programs are usually [[compiler|compiled]] or [[assembler|assembled]] from a series of smaller modules of [[source code]], producing a like number of '''relocatable binary''' modules, containing the low-level [[object code|binary]] [[instruction]]s and data 'understood' by a given [[Central Processing Unit|CPU]]. These modules, which can be easily modified to operate at any [[address]] in [[main memory]], can later be [[linking|linked]] together to produce an executable binary object.
  
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This involves two logical stages (although often the the software doing the linking, the '''linker''', merges them together, in actual operation).
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In addition to the instructions (in binary form) and data, a relocatable binary module contains other information, needed for the linking process. It includes a 'symbol table'; a list of:
  
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In the first, the linker must pick an address at which to place each binary module, and modify the binary of each module to function at that address.
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* all the names on all out-going references to other modules;
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* the names which this module contains within it;
  
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The second stage is one in which references from one module to names in another are 'resolved', and the binary in the module which is making the 'external' reference is modified to properly refer to the location in the module where the reference is to be found.
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There is also 'relocation' information, noting the words in this module which need to be modified during the linking process, and exactly what type(s) of modifications are needed for each.
  
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In addition to the instructions (in binary form), a relocatable binary module contains other information, needed for the linking process. It includes a 'symbol table' (a list of i) all the names on all out-going references to other modules, and ii) the names which this module contains within it); and also 'relocation' information, noting the words in this module which need to be modified during the linking process, and what exactly what type(s) of modifications are needed for each.
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[[Category: Software Basics]]

Latest revision as of 22:16, 9 October 2022

Larger programs are usually compiled or assembled from a series of smaller modules of source code, producing a like number of relocatable binary modules, containing the low-level binary instructions and data 'understood' by a given CPU. These modules, which can be easily modified to operate at any address in main memory, can later be linked together to produce an executable binary object.

In addition to the instructions (in binary form) and data, a relocatable binary module contains other information, needed for the linking process. It includes a 'symbol table'; a list of:

  • all the names on all out-going references to other modules;
  • the names which this module contains within it;

There is also 'relocation' information, noting the words in this module which need to be modified during the linking process, and exactly what type(s) of modifications are needed for each.

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