[LLVMdev] A new mechanism to compiler kernel modules using llvm: Defer type evaluation in clang?

[Jovi Zhang]

Hi,

First of all, I didn't study on compiler too much, I'm a Linux kernel developer,
Now I have one idea about compile kernel module by using llvm framework.

In Linux world, traditionally compile Linux kernel module only have one way:
compile it to machine code directly, deploy to target machine, then
run it in target machine.

This have some problem from long term view, especially kernel module
compatibility issue,
we know that Linux kernel change fast, when kernel change the data
structure exposed to external
kernel modules, then all ko depend on that data structure will need
recompile, one case is
kernel upgrade.
This is really a problem, we already suffered it many years, in whole
Linux world.
Linux distribution suffer it, third party kernel modules developers suffer it.
hardware driver developers also suffer it, we cannot avoid re-compile
kernel modules whenever new kernel
release if the structure changed, why? because kernel modules depend
on kernel header data structure, this is the point.

Is there have any method to fix it? let's try to decouple kernel
modules with kernel, by using llvm.
Please give comments on following mechanism, 3 steps:

1) kernel modules developer compile C file into high level IR, not to
machine code.

2) In install time, the high level IR file "link" with kernel header
data structure file, generate  low level
IR file, it could be .bc or .ll file in llvm form.

3) llvm compile the low level IR file into machine code in target
machine, then insert kernel modules, run it.

Using this method, kernel module code is not need to change when
kernel header file change, because it evaluate
structure type info at install time, not C code compile time. it fix
compatibility  issue in a clean way.
The key point of this method is we need defer structure type
evaluation into install time, Is Clang support
this "feature" at present?

How about this idea sounds? I really think llvm design is nature to
suit this idea, benefit from llvm's IR.
If we really implement this idea, it would be very valuable for whole
Linux community, trust me:)

I would appreciate if you can give me some technical comments on this design.
Thanks very much.

.jovi