Messages in this thread | | | Subject | Re: [PATCH 0/2] jump label: update for .39 | From | Steven Rostedt <> | Date | Thu, 10 Mar 2011 10:38:24 -0500 |
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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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