Does glibc require a MMU?

Does glibc require a MMU?

[Chris Packham]

Hi,

I'm looking at tidying some things up in crosstool-ng. Currently we
don't allow selecting GLIBC if the architecture doesn't support a MMU.
A user pointed out that that means that we can't build a
m68k-linux-gnu toolchain but per the GLIBC README that configuration
is supported.

I think the specific case of m68k is a bit subtle because there are
MMU-less variants. So while the architecture clearly allows for a MMU
not all variants of the CPU will have one. I probably will set the
flag to say m68k supports a MMU but I'm wondering if more generally I
should just allow glibc to be selected regardless of MMU support.

Thanks,
Chris

Re: Does glibc require a MMU?

[Carlos O'Donell]

On Fri, Sep 22, 2023 at 8:10 PM Chris Packham via Libc-help
<libc-help@sourceware.org> wrote:
> I'm looking at tidying some things up in crosstool-ng. Currently we
> don't allow selecting GLIBC if the architecture doesn't support a MMU.
> A user pointed out that that means that we can't build a
> m68k-linux-gnu toolchain but per the GLIBC README that configuration
> is supported.

We have 3 valid and supported ~m68k ABIs:
https://sourceware.org/glibc/wiki/ABIList#m68k

The supported ColdFire targets have an MMU.

> I think the specific case of m68k is a bit subtle because there are
> MMU-less variants. So while the architecture clearly allows for a MMU
> not all variants of the CPU will have one. I probably will set the
> flag to say m68k supports a MMU but I'm wondering if more generally I
> should just allow glibc to be selected regardless of MMU support.

You need an MMU to support running glibc, the implementation of the
dynamic loader, and certain functions and algorithms depend on having
an MMU to do certain operations with memory mappings.

How you choose to express this in cross-toolng is up to you, and whatever
serves your users best :-)

Cheers,
Carlos.