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Re: [RFC] Add asm constraint modifier to mark strict memory accesses

On 09/18/14 08:38, Yury Gribov wrote:
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?
I think cross posting is fine. Most of us don't necessarily watch the kernel or glibc lists -- and in this case I think those cross list discussions could be extremely valuable.


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