Messages in this thread | | | Date | Thu, 10 Mar 2011 09:11:39 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH 0/2] jump label: update for .39 |
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* 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 ?
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
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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