On Mon, 5 Jul 2010, Andriy Gapon wrote:
on 02/07/2010 11:29 Bjoern A. Zeeb said the following:
On Fri, 25 Jun 2010, Andriy Gapon wrote:
Hey,
Proposed patch skips zero sized sections without going into trouble of
allocating section entry (progtab), doing zero-sized memory allocs and
copies.
I observe that sometimes zero-sized set_pcpu sections are produced in
module
objects, maybe when a module doesn't create any per cpu data of its
one, but
references external pcpu data. Not sure.
[snip]
This work is based on np@'s investigation and original patch:
http://lists.freebsd.org/pipermail/freebsd-hackers/2009-November/030093.html
Have you guys figured this out already?
By 'this' - do you mean why that zero-sized section is produced at all?
Does it really matter why that happens?
Well, no, I was thinking of the workaround and going ahead to commit
somehting;)
I stated my guess already. Now I see that it is enough to simply include
sys/pcpu.h for this to happen. Inline assembly at the start of the said header
unconditionally creates the section. If DPCPU_DEFINE is never used in a module,
then set_pcpu section remains empty. Neither compiler nor linker have any
reason
to drop empty sections in the build process for amd64 modules.
I am not sure if ".section set_pcpu" assembly can be made conditional or moved
some place else, so that the section is only created when DPCPU_DEFINE is
actually
used.
The same applies to VIMAGE btw. Same technique.
/bz
--
Bjoern A. Zeeb From August on I will have a life. It's now up to you
to do the maths and count to 64. -- Bondorf, Germany, 14th June 2010
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