On 09/18/2014 05:36 PM, Jeff Law wrote:
On 09/18/14 05:19, Yury Gribov wrote:
Would that modifier mean that the inline asm is unconditionally reading
resp. writing that memory? "m"/"=m" right now is always about might
read or might write, not must.
Yes, that's what I had in mind. Many inline asms (at least in kernel) do
read memory region unconditionally.
That's precisely what I'd expect such a modifier to mean. Right now
memory modifiers are strictly "may" but I can see a use case for "must".
I think the question is will the kernel or glibc folks use that new
capability and if so, do we get a significant improvement in the amount
of checking we can do. So I think both those groups need to be looped
into this conversation.
Right. Should I x-post or better send separate emails and then report
feedback on GCC list?
From an implementation standpoint, are you thinking a different
modifier (my first choice)?
So we have constraints ("m", "v", "<", etc.) and modifiers which can be
attached to arbitrary constraints ("+", "=", "&", etc.). I though about
adding a new modifier so that it could be added to arbitrary memory
constraint as needed.
That wouldn't allow us to say something
like the first X bytes of this memory region are written and the
remaining Y bytes may be written, but I suspect that's not a use case
we're likely to care about.
Yeah, I don't think anyone needs this.
-Y
