Re: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c"

David Hildenbrand
2020-10-23T16:33:24Z

On 23.10.20 16:47, 'Greg KH' wrote:
> On Fri, Oct 23, 2020 at 02:39:24PM +0000, David Laight wrote:
>> From: David Hildenbrand
>>> Sent: 23 October 2020 15:33
>> ...
>>> I just checked against upstream code generated by clang 10 and it
>>> properly discards the upper 32bit via a mov w23 w2.
>>>
>>> So at least clang 10 indeed properly assumes we could have garbage and
>>> masks it off.
>>>
>>> Maybe the issue is somewhere else, unrelated to nr_pages ... or clang 11
>>> behaves differently.
>>
>> We'll need the disassembly from a failing kernel image.
>> It isn't that big to hand annotate.
>
> I've worked around the merge at the moment in the android tree, but it
> is still quite reproducable, and will try to get a .o file to
> disassemble on Monday or so...

I just compiled pre and post fb041b598997d63c0f7d7305dfae70046bf66fe1 with

clang version 11.0.0 (Fedora 11.0.0-0.2.rc1.fc33)

for aarch64 with defconfig and extracted import_iovec and
rw_copy_check_uvector (skipping the compat things)

Pre fb041b598997d63c0f7d7305dfae70046bf66fe1 import_iovec
-> https://pastebin.com/LtnYMLJt
Post fb041b598997d63c0f7d7305dfae70046bf66fe1 import_iovec
-> https://pastebin.com/BWPmXrAf
Pre fb041b598997d63c0f7d7305dfae70046bf66fe1 rw_copy_check_uvector
-> https://pastebin.com/4nSBYRbf
Post fb041b598997d63c0f7d7305dfae70046bf66fe1 rw_copy_check_uvector
-> https://pastebin.com/hPtEgaEW

I'm only able to spot minor differences ... less gets inlined than I
would have expected. But there are some smaller differences.

Maybe someone wants to have a look before we have object files as used
by Greg ...

--
Thanks,

David / dhildenb