Re: [Qemu-ppc] [Qemu-devel] [PATCH] ppc: Stop dumping state on all exceptions in linux-user

[Peter Maydell]

On 3 August 2016 at 12:28, Benjamin Herrenschmidt
<address@hidden> wrote:
> To the best of my understanding we only ever generate
> 0x40000000 and 0x42000000 via ppc_cpu_handle_mmu_fault()
> in user_only_helper.c unless there's another path to DSI
> in user mode that I missed.
>
> That being said, the comment isn't useful anyway. Nobody
> looks at it :-)

Well, it means when somebody does come along to clean
up the code or just to read it they have some idea of
whether the code is believed-to-be-good or not.

> I can respin with the comment back in or do put some blurb
> in the cset comment, let me know.

I think if you're going to remove the comment you should
specifically say you're doing it because you believe the
code is actually correct.

> BTW. I noticed, the generic path from the original signal
> coming from the host kernel through to here loses the
> information that would allow us to differenciate between
> a map error (no mapping) or a protection fault.
>
> It's a bit unfortunate, not sure if we can do much about it
> though without stopping to hijack the existing MMU translate
> hook in the CPU class and using a user mode dediated one that
> takes that sort of info as an argument.

Yeah, there's an LTP test that fails because of this (we
send a SIGSEGV when we should be sending a SIGBUS). It's
a bit painful to fix though, since as you say we've
effectively thrown away some information. I'm inclined to
put this in the big pile of "bugs we could fix if we
ever implemented linux-user-with-softmmu" and otherwise
ignore it, unless you have a real-world program that
needs this and makes some kind of bodge fix worthwhile.

thanks
-- PMM