Messages in this thread | | | Date | Thu, 15 Feb 2024 22:09:42 -0800 | Subject | Re: [PATCH v8 2/2] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6_magic tests | From | Guenter Roeck <> |
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On 2/15/24 21:54, Helge Deller wrote: [ ... ] > > Can you please give a pointer to this test code? > I'm happy to try it on real hardware. > You should also see the problem if you use v7 of Charlie's checksum unit test fixes.
I submitted the qemu fix (or at least what I think the fix should be) a couple of minutes ago.
https://patchwork.kernel.org/project/qemu-devel/patch/20240216053415.2163286-1-linux@roeck-us.net/
>> It is quite easy to show that carry is always set after executing ldd >> on an unaligned address. That is also why I know for sure that the >> problem is not seen with ldw on unaligned addresses. > Interesting.
Ultimately it wasn't surprising, with the unusual carry bit implementation on hppa. The upper 8 carry bits were not masked correctly when returning from a trap or interrupt.
> In general I think it's quite important to differentiate between > running on qemu or running on physical hardware.
I know, that makes testing always tricky (not just with this architecture) because it is often not obvious if the problem is a problem in the tested code or a problem in the emulation.
> Qemu just recently got 64-bit support, and it's not yet behaving > like real hardware. One thing I noticed is, that read hardware > does not seem to jump into the exception handler twice, while > qemu does. So, if you run into an exception (e.g. unaligned ldd) > then if a second exception happens in the fault handler (e.g. second > unaligned ldd to resolve wrongly-coded code lookup), you will > get different behaviour between hardware and emulation.
Hmm, interesting. Makes me wonder how the real hardware handles such double traps.
> This is also the reason why qemu still fails to emulate newer > 64-bit Linux kernels which uses kernel modules. > I don't use modules in my testing, so I'll leave that alone for anther day.
Cheers, Guenter
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