[P4-design] undefined reads

Mihai Budiu mbudiu at vmware.com
Mon Jun 19 14:18:05 EDT 2017


The C guys have a lot of constraints for backwards compatibility.
We can do better.

Mihai

From: P4-design [mailto:p4-design-bounces at lists.p4.org] On Behalf Of Vladimir Gurevich
Sent: Saturday, June 17, 2017 1:10 PM
To: Nate Foster <jnfoster at cs.cornell.edu>
Cc: p4-design <p4-design at lists.p4.org>
Subject: Re: [P4-design] undefined reads

Hi Nate,

This is a truly fascinating read! Thanks for the pointer.

For me, the main takeaway, though, is that perhaps we should take it easy :)  If C guys couldn't figure it out in 28 years (counting from C89 to be more than fair) or more, we can probably wait a year or two so that we gain some experience :) In fact, I was just about to make a comment on another thread that it is not clear to me how well C spec defines these undeterminate (I like this term from the article) behaviors.

I think the general statements Andy is proposing a probably already better than what you can find in many other places.

Thanks,
Vladimir



On Sat, Jun 17, 2017 at 7:06 AM, Nate Foster <jnfoster at cs.cornell.edu<mailto:jnfoster at cs.cornell.edu>> wrote:
Hi folks,

We've had a lot of past discussion (and some ongoing discussion) about undefined values / behavior. Here is a nice ACM Queue that outlines some of these issues in the context of C. I think it's worth a read.

http://queue.acm.org/detail.cfm?id=3041020<https://urldefense.proofpoint.com/v2/url?u=http-3A__queue.acm.org_detail.cfm-3Fid-3D3041020&d=DwMFaQ&c=uilaK90D4TOVoH58JNXRgQ&r=tGW6TKXajnoXSyy1S1P4DHGPe8sj54GGvw-b21n7aWg&m=oW056L6T2qxLzcdAw3CZqg6VjOG155YnDdpI0m67MAI&s=62k0TE3XcF3-0ovuaDrEM5r8O-y3GUmM79G9glfYFEg&e=>

-N

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