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    SubjectRe: [PATCH 0/2] jump label: update for .39
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    On Thu, 2011-03-10 at 09:11 -0500, Mathieu Desnoyers wrote:
    > * Steven Rostedt (rostedt@goodmis.org) wrote:
    > > On Wed, 2011-03-09 at 15:47 -0500, Jason Baron wrote:
    > > > Hi,
    > > >
    > > > Re-fresh of updates against latest -tip tree.
    > >
    > > Thanks Jason,
    > >
    > > I started looking at them, I should have comments tomorrow (if I have
    > > any comments ;)
    > >
    > > >
    > > > I've tried to split this update up somewhat, but I've only succeeded to split
    > > > out the dynamic debug bits. The interface changes and re-write are quite
    > > > intertwined.
    > > >
    > > > I believe this update should address all the comments from the previous posting
    > > > except for Mathieu's request for a section of jump label pointers that point to
    > > > the jump label structures (since the compiler might leave gaps in the jump label
    > > > structures).
    > >
    > > The jump label structures is a list of 3 pointers, correct? I doubt that
    > > gcc would place any holes in it as they are all aligned by natural word
    > > size.
    > >
    >
    > Hi Steven,
    >
    > Can you explain what would prevent gcc from aligning these 3 pointers
    > (total of 24 bytes on 64-bit architectures) on 32-bytes ? Also, could
    > you point out what would refrain the linker from aligning the start of
    > object sections on the next 32-bytes (thus power of two) address
    > multiple ?

    Maybe it would be just easier to add another long ;)

    Seriously, it would. Then it would be 32 bytes on 64bit and 16 bytes on
    32bit. Then I guess we can have our guarantee without doing a large
    change to have this indirect pointer and still waste sizeof(long) bytes
    in having it.

    Just insert a long "Reserved" word.

    -- Steve

    >
    > I think we need to be a bit more strict in our interpretation of what
    > guarantee gcc/ld provide and don't provide with respect to section and
    > structure alignment.
    >
    > As it stands now, the section alignment of jump labels looks half-broken
    > on most architectures, and this *is* a big deal. I would really like to
    > see a patch for this (it can be a separate patch) going in for .39.
    >
    > Thank you,
    >
    > Mathieu
    >




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