From: dds@aueb.gr (Diomidis Spinellis)
Subject: [TUHS] Unix & Memory Management Units (MMU)
Date: Wed, 7 Dec 2016 19:31:22 +0200 [thread overview]
Message-ID: <32c3f08c-9c04-bdeb-82b2-2bfcf1757ddd@aueb.gr> (raw)
In-Reply-To: <12385.1481129198@cesium.clock.org>
On 07/12/2016 18:46, Erik E. Fair wrote:
> One imagines that many pointer mistakes (bugs) in assembly or C were
> discovered and squashed in that version, modulo the historical
> unhappiness resulting from address zero containing a zero if
> dereferenced ("NULL pointers") in process address space.
I remember Jan-Simon Pendry telling me in the 1980s, that the NULL
dereference check was first introduced in SunOS with much pain due to
the resulting crashes. In BSD Unix, which preceded it, the VAX MMU was
setup with a page in virtual address 0 that would contain the value 0 at
that address. (BSD Unix offered memory protection. I assume it had this
setup for backward compatibility.)
next prev parent reply other threads:[~2016-12-07 17:31 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-07 16:46 Erik E. Fair
2016-12-07 17:31 ` Diomidis Spinellis [this message]
2016-12-07 18:49 ` Clem Cole
2016-12-07 17:10 Noel Chiappa
2016-12-07 17:51 Noel Chiappa
2016-12-07 20:12 Noel Chiappa
2016-12-07 21:00 ` Earl Baugh
2016-12-08 10:39 ` Joerg Schilling
2016-12-08 8:50 ` Paul Ruizendaal
[not found] <mailman.13.1481217534.3779.tuhs@minnie.tuhs.org>
2016-12-08 18:11 ` Johnny Billquist
2016-12-08 19:24 ` Paul Ruizendaal
2016-12-08 19:32 ` Lars Brinkhoff
2016-12-08 19:44 Paul Ruizendaal
2016-12-08 20:38 Noel Chiappa
2016-12-08 22:39 ` Paul Ruizendaal
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