how load addresses chosen for shared libs in 64/b OS? - Linux

This is a discussion on how load addresses chosen for shared libs in 64/b OS? - Linux ; Does someone know how 64 bit linux systems decide where to physically load shared libraries, such as the C library? We have 3 systems, that are (redhat enterprise 4) and except for such things as hostname, are otherwise believed to ...

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Thread: how load addresses chosen for shared libs in 64/b OS?

  1. how load addresses chosen for shared libs in 64/b OS?

    Does someone know how 64 bit linux systems decide where to
    physically load shared libraries, such as the C library? We have 3
    systems, that are (redhat enterprise 4) and except for such things
    as hostname, are otherwise believed to be identical. Yet on each of
    these 3 systems, we notice that the shared libraries load into a
    different virtual address range. However, they load in the same
    place on each system by itself. It's almost as
    though the choice somehow uses some particulars of the system (e.g.
    hostname) in an algorithm to insure that the load addresses are not
    exactly the same (maybe for some security reason) on each system.

    We have exec shield on, but randomize off.

    Also, we were also wondering if there was an easy way to have 64
    bit linux load the libraries in a different place on the same
    machine, without changing the program (to simulate loading on a
    second machine). Is that what the randomize of exec shield would
    do (I don't have root privs, so I can't test it for now).

    Any information or hints as to where in the kernel source code to
    look would be appreciated. In the 32 bit world, I recall a variable,
    (something like, TASK_UNMAPPED_BASE) that would be computed at
    compile or linux build time based on the particulars of the system.
    Is there such a variable still in use in the 64 bit OS?




  2. Re: how load addresses chosen for shared libs in 64/b OS?

    (looks like me and Mr Braun had a race condition, his post occurred
    while I wascomposing mine - sorry)




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