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Re: Spectre V1 diagnostic / mitigation
* Richard Biener:
> On Wed, 19 Dec 2018, Florian Weimer wrote:
>> * Richard Biener:
>> > The cost is probably target dependent - on x86 it's simply a $fs based
>> > load/store.
>> Do you need to reserve something in the TCB for this?
> No idea. But I figured using TLS with the patch only works when
> optimizing and not with -O0. Huh. Anyway, it should be equivalent
> to what presence of
> __thread void *_SV1MASK = (void *)-1l;
> requires (plus I make that symbol GNU_UNIQUE). I see this
> allocates -1 in the .tdata section marked TLS.
Oh. That's going to be substantially worse for PIC, even with the
initial-exec model, especially on architectures which do not have
arbitrary PC-relative loads. Which is why I'm asking about the TCB