Date: Tue, 3 Nov 2020 13:16:13 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: xtouqh@hotmail.com Cc: Hans Petter Selasky <hps@selasky.org>, hackers@freebsd.org Subject: Re: KASSERT(val != 0) not triggering in linux_errno.c reading outside of array Message-ID: <20201103111613.GP2654@kib.kiev.ua> In-Reply-To: <AM0PR06MB3986D1AA1E59725F4D677727C0110@AM0PR06MB3986.eurprd06.prod.outlook.com> References: <AM0PR06MB39867F0AE62A737D2EE596F5C0110@AM0PR06MB3986.eurprd06.prod.outlook.com> <77d2eef0-9cc8-aa39-6d28-a7fb41e233ac@selasky.org> <AM0PR06MB398671E9C991E0A1B4223660C0110@AM0PR06MB3986.eurprd06.prod.outlook.com> <c87d3aef-7a66-48bb-ca9e-fe4ae4e9f1d3@selasky.org> <AM0PR06MB3986D1AA1E59725F4D677727C0110@AM0PR06MB3986.eurprd06.prod.outlook.com>
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On Tue, Nov 03, 2020 at 01:17:51PM +0300, xtouqh@hotmail.com wrote:
> Hans Petter Selasky wrote:
> > Hi,
> >
> > Should:
> >
> > for (i = 1; i < sizeof(linux_errtbl); i++) {
> >
> > Be:
> >
> > for (i = 1; i < sizeof(linux_errtbl)/sizeof(linux_errtbl[0]);
> > i++) {
> >
> >
> > Or:
> >
> > for (i = 1; i < (int)nitems(linux_errtbl); i++) {
>
> That's right, and I added the same comment in the review. My question is
> different though -- with the issue present, KASSERT() should have triggered
> (there are 0 values with incorrect indexes, added printf() confirms that)
> exposing the bug, but it does not -- WHY? -- I just want to understand
> what's going on.
I think this is a poster child for the current undefined behaviour treatment
by compilers. You are accessing beyond array last element, and compiler can
prove it, so it allowed to do anything.
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