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

From: Linus Torvalds
Date: Thu Aug 13 2015 - 17:46:58 EST

On Thu, Aug 13, 2015 at 2:42 PM, Raymond Jennings <shentino@xxxxxxxxx> wrote:
> I am curious about what's supposed to happen normally on signal delivery.
> Is SS a register that's supposed to be preserved like EIP/RIP and CS when a
> signal is delivered?

What exactly does "supposed" mean?

On x86-64, we traditionally haven't touched SS, because it doesn't
really matter in 64-bit long mode. And apparently dosemu depended on
that behavior.

So clearly, we're not "supposed" to save/restore it. Because reality
matters a hell of a lot more than any theoretical arguments.

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