On 24/08/13 23:08, Edward Z. Yang wrote:
Part of the resource limits work needs to access the bdescr for a thunk
when it is entered. Of course, right now, this needs to go through
HEAP_ALLOCED; I imagine this would way to slow to put into the generated
code. So I happened across this page describing some previous efforts
to get rid of the HEAP_ALLOCED check:
http://ghc.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/HeapAlloced
So I'm currently implementing method 2, and I'm wondering what the best
way to setup the indirection table might be: maybe some sort of
null-terminated array? What's the proper way for the linker to figure
out where the indirection table lives?
Getting rid of HEAP_ALLOCED would be wonderful! And I'm really glad I
wrote that wiki page, I had completely forgotten about those ideas.
It seems to me that what we want to do at starting is like a GC: we
traverse all the static objects copying them to a new area and updating
all the internal pointers at the same time.
You can arrange that all the indirections end up next to each other by
putting them in a special section. Then you can traverse the contents
of the section so long as you have a symbol at the beginning and the
end, or something like that. There are other ways to do it, such as
having the module initialisation code register something with the RTS.
It pains me to have to use this solution when what we really ought to do
is memory-mapping tricks to put the static objects where we want them.
Cheers,
Simon
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