[LLVMdev] how to track down a kernel miscompilation?
andrewl at lenharth.org
Mon Nov 24 09:56:26 PST 2008
On Mon, Nov 24, 2008 at 11:39 AM, John Regehr <regehr at cs.utah.edu> wrote:
> Hey that is great to hear that the volatile stuff is helping someone.
Yes, quite a bit. The 2.4 port we did we had to throw in asm no-ops
with "clobbers memory" to enforce volatile. None of that was
necessary this time.
> Just broadly speaking do you know if the instcombine bug involves pointer
> code vs. scalar? I ask because intensive random testing has not found the
> bug that you are seeing. That says that either (1) the bug lies in a part
> of the program space we don't explore or (2) it does, but we haven't run
> the tests for long enough. The former sounds most likely to me. If I
> knew more about what kind of code evoked the problem we could give high
> priority to adding the appropriate extensions to our testcase generator.
I don't know. If edwin doesn't beat me to it (and he probably will),
it will get tracked down to the file or files.
> On Mon, 24 Nov 2008, Andrew Lenharth wrote:
>> On Mon, Nov 24, 2008 at 10:51 AM, John Regehr <regehr at cs.utah.edu> wrote:
>>>> was wrong. At the time (~ 1 year ago) it was almost always
>>>> instcombine and almost always volatile related. Now bugpoint has some
>>>> ways to run the code by some external agent which I haven't
>>>> investigated yet.
>>> People have fixed a ton of bugs (volatile and otherwise) in instcombine
>>> since then. I will be very interested to hear what pass ends up being the
>>> problem here, and what exactly is the code that triggers the bug-- please
>>> post these when the results are known.
>> Yes, the rash of volatile bug fixes made getting 2.6 working much much
>> easier than getting 2.4 originally was. Unfortunately I am in the
>> middle of prepping a paper so I can't track down the current
>> instcombine bug, but I've posted a building and working kernel should
>> other people want to play with llvm compiled linux kernels.
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