[TUHS] Memory management in Dennis Ritchie's C Compiler

Dibyendu Majumdar mobile at majumdar.org.uk
Tue Aug 18 06:43:59 AEST 2020

On Mon, 17 Aug 2020 at 21:34, Paul Winalski <paul.winalski at gmail.com> wrote:
> On 8/17/20, Dibyendu Majumdar <mobile at majumdar.org.uk> wrote:
> >
> > Yes, it only uses sbrk(). One consequence I think is that sbrk()
> > expands the process memory without invalidating existing use of memory
> > - so the code is able to periodically expand heap while retaining all
> > existing allocations.
> If everyone does that, you can call other people's code without fear
> of stepping on their memory when you allocate memory in your code.
> Using a negative value to decrease the break is more problematic.
> malloc() usually uses sbrk() to extend its heap.
> When we ported DEC's GEM compilation system to Unix, I used sbrk() to
> extend memory and built my own multiple heap allocation scheme on top
> of that.  I could have used malloc() to allocate the heap chunks, but
> there was no point.  Might as well cut out the middleman.

Unfortunately sbrk() is not portable (I am building on Windows with
MSVC too) and as far as I know was even removed from POSIX.

>From Wikipedia:
sbrk and brk are considered legacy even by 1997 standards (Single UNIX
Specification v2 or POSIX.1-1998).[5] They were removed in


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