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From: dricej@drilex.UUCP (Craig Jackson)
Newsgroups: comp.os.minix,comp.unix.wizards
Subject: Re: what does brk do on segmented architectures?
Message-ID: <214@drilex.UUCP>
Date: Mon, 5-Oct-87 08:59:02 EDT
Article-I.D.: drilex.214
Posted: Mon Oct  5 08:59:02 1987
Date-Received: Thu, 8-Oct-87 03:17:55 EDT
References: <94@rocksvax.UUCP>
Reply-To: dricej@drilex.UUCP (Craig Jackson)
Organization: Data Resources/McGraw-Hill, Lexington, MA
Lines: 15
Summary: 'brk' has a linear address space assumption
Xref: mnetor comp.os.minix:1804 comp.unix.wizards:4698

'brk' and 'sbrk' are two Unix system calls which are very difficult to
implement on many systems.  They assume a linear address space used linearly.
Most systems which don't have both these characteristics either kluge around
them or don't implement them at all.  For example, I believe that some
Apollo implementations just reserved some memory for 'brk', and when you
something else in the address space, that was all.  (I don't know if their
current version does this; not relevant.)

For non-linear address spaces, such as Zilogs or Intels, generally there is
no simple 'sbrk' or 'brk', except in the degenerate memory models.  Generally
there is one 'brk' per segment, and a call which sets it.
-- 
Craig Jackson
UUCP: {harvard!axiom,linus!axiom,ll-xn}!drilex!dricej
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