On Fri, Mar 27, 2015 at 7:25 AM, Denys Vlasenko <dvlas...@redhat.com> wrote:
>
> Apparently, users *don't* depend on arithmetic flags
> to survive over syscall. They also okay with DF flag
> being cleared.
Generally, users probably dont' care about many registers at all being
saved, but it's worth noting that the reason system calls save/restore
even caller-saved registers is at least partly in order to avoid any
kernel information leaks.
I don't believe that user mode will ever reasonably care about the
arithmetic flags being changed, but at the same time I also don't it
is something we should ever consider a "feature" we should try to take
advantage of. Generally we should try to not mess with the flag state,
and I'd *much* rather make the rule be that all the system call return
paths restore flags as much as possible.
Linus
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