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    Subjectkbuild: improved Section mismatch detection
    I have spent the last week (the time I can afford to
    Linux stuff anyway) to improve the Section mismatch
    warnings detected by modpost.

    The problem until now has been that the Section
    mismatch warnings were dependent on the actual
    configuration of HOTPLUG, HOTPLUG_CPU and MEMORY_HOTPLUG.
    In the default configuration with HOTPLUG enbaled most
    of the remaining Section mismatch warnings were not
    seen and thus many of us thought that everything was great.

    Adrian reminded us that KCFLAGS=-fno-inline told
    another story with more than 100 Section mismatch
    warnings on 64 bit x86 with an allyesconfig build.

    As this was not acceptable I set out to make it
    less configuration dependent. To do so I quikly
    relaised that modpost had to be prepared before this
    was a feasible thing to implment.

    This serie of patches is:

    1) kbuild: fix so modpost can now check any .o file
    2) kbuild: try harder to find symbol names in modpost
    3) kbuild: code refactoring in modpost
    4) kbuild: introduce blacklisting in modpost
    5) kbuild: check section names consistently in modpost
    6) all archs: consolidate init and exit sections in
    7) compiler.h: introduce __section()
    8) Use separate sections for __dev/__cpu/__mem code/data

    Patch 6) makse a set of trivial changes in all arch files
    and the reason why I copid linux-arch on this mail.

    Patch 4) is a major change in modpost where we no longer try to
    find all the good guys but instead look for the bad combinations.
    This should result in a lot less false warnings and for example got
    rid of an irritating warning on sparc64.

    Patch 2) is important - previously modpost failed to find the
    correct symbol based on address lookup because it wanted an exact
    match. Allowing up to 20 bytes offset we now locate almost all
    symbols and the warnings are much easier to fix.

    Randy and Adrian among others have done a great job fixing
    many Section mismatch warnngs over the last month.
    But frankly much more people should do this and I can see people
    ignoring the warnings.

    Therefore the plan is to turn the warnings into hard build errors
    at -rc1 time.
    This should force people to actually fix the warnings they introduce.

    But to do so we need the warnings we have today gettign fixed and
    the new improved modpost should help you here.
    To further help the plans are to:
    - add a config option to enable -fno-inline (or a similar option)
    - make the warnings from modpost more descriptive but longer
    - maybe to spend a few hours to fix some of the obvious candidates
    Less than half an hour for each warning for the trivial cases
    - Maybe start using __INIT and friends in assembler code
    xen had two bugs in this area recently for example.

    It has been questions if it is worth the effort to fix these warnings.
    Randy just fixed three oops candidates - do anyone need more facts?

    And the cpu code looks rather fragile in the dead/removed CPU cases.
    I see several references that will oops and is easy to fix.


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