Re: [regression] x86/signal/64: Fix SS handling for signals delivered to 64-bit programs breaks dosemu

From: Andy Lutomirski
Date: Wed Aug 12 2015 - 16:01:26 EST

On Wed, Aug 12, 2015 at 12:55 PM, Stas Sergeev <stsp@xxxxxxx> wrote:
> 12.08.2015 22:20, Andy Lutomirski ÐÐÑÐÑ:
>> current kernels, it stays switched. If we change this, it won't stay
>> switched. Even ignoring old ABI, it's not really clear to me what the
>> right thing to do is.
> There can be the following cases:
> - switch_userspace_thread() switches fs to non-zero selector
> - switch_userspace_thread() switches the fs base via syscall
> - switch_userspace_thread() switches fs in sigcontext
> - switch_userspace_thread() switches fs_base in sigcontext (???)
> What exactly case do you have in mind?
> I'd say, the way x86_32 is doing things - is good, but the
> bases... perhaps, in ideal world, they should be a part of
> the sigcontext as well?

Any of the above. What do you want the kernel to do, and how does the
kernel know you want to do that? The kernel has to pick *some*
semantics here.

Andy Lutomirski
AMA Capital Management, LLC
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