Fix-ups §

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Fix-ups are used to represent information in instructions which is currently unknown. During instruction encoding, if some information is unknown (such as a memory location of an external symbol), it is encoded as if the value is equal to 0 and a fix-up is emitted which contains information on how to rewrite the value when information is known.

The assembler goes through a stage of relaxation, applying fix-ups and modifying instruction values when they become known to the system. Once complete, any remaining fix-ups are converted to relocations and stored in the object file.

Source: Embecosm