[llvm-dev] [RFC] LLVM Busybox Proposal

Leonard Chan via llvm-dev llvm-dev at lists.llvm.org
Mon Jun 21 11:15:36 PDT 2021

> I think it's an interesting idea.  My main concern is that adding a new
> CMake
> option for this going to complicate the build system and make future CMake
> improvements more difficult.

That's fair. I'm working on a WIP version now and attempting to mitigate
the amount of CMake changes. Ideally, this would be controlled behind a
single CMake option that doesn't end-user behavior, and we would have an
upstream buildbot that could just enable this flag and ensure tools
dispatched through busybox work as-is.

> Do you have any idea of how much performance /
> toolchain size gains you will get from this approach?

Locally we've found resolving dynamic relocations takes about 20% of the
runtime for various dynamically linked LLVM tools. We'd have to double
check if this is still the case because recently there have been some
changes around semantic interposition that may help with this. I'm working
on a WIP version that we can compare against for size (that is, size of
separate tools + LLVM shared libs vs combined busybox size).
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