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From: Jan Hubicka <>
To: Jeff Law <>
Cc: Richard Biener <>,
Subject: Re: [PATCH] Improve DSE to handle stores before __builtin_unreachable ()
Date: Thu, 22 Jun 2023 15:42:33 +0200	[thread overview]
Message-ID: <ZJRPyeuKxXHfI/> (raw)
In-Reply-To: <>

> On 6/22/23 00:31, Richard Biener wrote:
> > I think there's a difference in that __builtin_trap () is observable
> > while __builtin_unreachable () is not and reaching __builtin_unreachable
> > () invokes undefined behavior while reaching __builtin_trap () does not.
> > 
> > So the isolation code marking the trapping code volatile should be
> > enough and the trap () is just there to end the basic block
> > (and maybe be on the safe side to really trap).
> Agreed WRT observability -- but that's not really the point of the trap and
> if we wanted we could change that behavior.
> The trap is there to halt execution immediately rather than letting it keep
> running.  That was a design decision from a security standpoint. If we've
> detected that we're executing undefined behavior, stop rather than
> potentially letting a malicious actor turn a bug into an exploit.

Also as discussed some time ago, the volatile loads between traps has
effect of turning previously pure/const functions into non-const which
is somewhat sad, so it is still on my todo list to change it this stage1
to something more careful.   We discussed internal functions trap_store
and trap_load which will expand to load/store + trap but will make it
clear that side effect does not count to modref.

I wanted to give it some time if I can come with something better, but
didn't so far.


  reply	other threads:[~2023-06-22 13:42 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2023-06-20 13:27 ` Jeff Law
2023-06-21  6:41   ` Richard Biener
2023-06-21  9:55     ` Jan Hubicka
2023-06-21 14:04     ` Jeff Law
2023-06-22  6:31       ` Richard Biener
2023-06-22 13:36         ` Jeff Law
2023-06-22 13:42           ` Jan Hubicka [this message]
2023-06-24 14:24             ` Jeff Law
2023-06-25 16:33               ` Jan Hubicka
2023-06-26 17:21   ` Jan Hubicka
2023-06-26 22:37     ` Jeff Law
2023-06-20  6:59 Richard Biener

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