[uClibc] mmaps for malloc should be private

[David McCullough]

Jivin Alexandre Oliva lays it down ...
> On Mar 21, 2004, David McCullough <davidm at snapgear.com> wrote:
> 
> > The dynamic loader doesn't run on uClinux (AFAIK ;-)
> 
> It does.  At least on frv-uclinux.

Ok,  I have never bumped into frv-uclinux.  A quick Google didn't
show up any sites where I could look at the source etc.  Do you have a
pointer to it ?  All I can find are gcc/binutils references and a few
hints of the uClinux port for it.

Do you have full shared libraries working under frv-uclinux ?

> > The basic problem is that on uClinux systems,  private mappings fail and
> > always have
> 
> Not on frv-uclinux, for sure.  Does it really, on other uClinux ports?
> I hope not.

If you look in linux-2.4.x/mmnommu/mmap.c you will find that all uClinux
ports on uclinux.org do not support private mappings.

http://cvs.uclinux.org/cgi-bin/cvsweb/uClinux-2.4.x/mmnommu/mmap.c?rev=1.21&content-type=text/x-cvsweb-markup

Search for "Get the NO_MM specific checks done first" in do_mmap_pgoff.

It explicitly prevents writable file mappings and writable private
mappings.

The first is obvious,  it isn't possible.  The second is arguable.

I believe the reasoning for this check is that you cannot have a private
mapping under uclinux as all memory is accessable.  This check forces
people to think about the NOMMUness of their target a little.  Not sure
I agree with it myself,  but it has been there a long time.

> > what you are trying to achieve with NOMMU libs on MMU systems ;-)
> 
> Running NOMMU apps on an MMU system is just a nice way to test the
> NOMMU apps, and to bootstrap an MMU libc port.

Fair enough.  So the FRV has MMU and NOMMU variants that are instruction
set compatible ?  Sounds like an interesting platform.  What sort of
bogoMIPs, internal devices etc do you get with one of these ?

Cheers,
Davidm

-- 
David McCullough, davidm at snapgear.com  Ph:+61 7 34352815 http://www.SnapGear.com
Custom Embedded Solutions + Security   Fx:+61 7 38913630 http://www.uCdot.org