[PATCH] D25467: [ELF] - Alternative fix to prevent possible crash on large output.

Davide Italiano via llvm-commits llvm-commits at lists.llvm.org
Mon Oct 17 15:06:08 PDT 2016

On Mon, Oct 17, 2016 at 2:26 PM, Rui Ueyama via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> This is a list of items that popped in my mind. Not exhaustive but probably
> good enough to start discussing what we should do next.
>  - FreeBSD: what is the status of building the entire FreeBSD system with
> LLD? Can it build everything including the kernel?

Another idea, which I discussed with Rafael and Michael a bit ago.
Implement support for order file. For starters, you don't need anything fancy.
Just get a list of symbols (which can be generated by systap or a
profiler) and pass that to the linker, so that sections are laid out
according to the partial order defined in the file (you can always
reconstruct a total order starting from a partial order using some
heuristic). This is particularly useful to improve startup time as you
reduce the amount of paging. Firefox uses this for sure, and
apparently ld64 implements this algorithm (or a slight variation of
it). I'm confident this is quite effective (see Martin Liska's thesis
which contains a more detailed description of the problem and
references https://arxiv.org/pdf/1403.6997.pdf)

Once this is done, and we convince ourselves is a good thing, we can
try implementing Pettis-Hansen ordering (guided by profiling
informations) as Srinaman did for gold.
That should help putting code accessed frequently together near to
reduce I-cache traffic etc..
I'm not sure if it's actually effective (I hope so), maybe
Srinaman/David have more informations about it.



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