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

Jean-Daniel Dupas devlists at shadowlab.org
Mon Apr 29 00:11:11 PDT 2013

Just out of curiosity, what would be the main benefit of this approach vs DKMS which is already widely used ?

Le 28 avr. 2013 à 18:42, Jovi Zhang <bookjovi at gmail.com> a écrit :

> 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
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-- Jean-Daniel

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