GCC -fPIC Option

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Position Independent Code means that the generated machine code is not dependent on being located at a specific address in order to work.

E.g., jumps would be generated as relative rather than absolute.

Pseudo-assembly:

  • PIC: This would work whether the code was at address 100 or 1000

    100: COMPARE REG1, REG2
    101: JUMP_IF_EQUAL CURRENT+10
    ...
    111: NOP

  • Non-PIC: This will only work if the code is at address 100

    100: COMPARE REG1, REG2
    101: JUMP_IF_EQUAL 111
    ...
    111: NOP

If your code is compiled with -fPIC, it's suitable for inclusion in a library. The library must be able to be relocated from its preferred location in memory to another address, there could be another already loaded library at the address your library prefers.