Re: Bypassing the 2/3/4GB virtual memory space on 32-bit ports

[Ivo De Decker <ivodd@debian.org>]

Hi,

On 8/9/19 4:41 PM, Karsten Merker wrote:
> On Fri, Aug 09, 2019 at 02:31:47PM +0200, Ivo De Decker wrote:
> > Some random notes (these are just my preliminary thoughts, not a new release
> > team policy):
> [...]
> > - We are talking about having both native 32-bit and 64-bit packages in
> >    the same environment. We are NOT talking about emulated builds. The
> >    resulting (32-bit) binaries still need to run natively in the build
> >    environment.
>
> Hello,
>
> this requirement poses a significant difficulty: while 64bit x86
> CPUs can always execute 32bit x86 code, the same isn't
> necessarily the case on other architectures. On arm, there is no
> requirement that an arm64 system has to be able to execute 32bit
> arm code and in particular in the arm server space, i.e. on the
> kind of hardware that DSA wants to have for running buildds on,
> 64bit-only systems are becoming more and more common. On RISC-V
> the 64bit and 32bit ISAs have been disjunct forever, i.e. there
> is no riscv64 system that can natively execute riscv32 code. I
> don't know what the situation looks like in mips and ppc/power
> land but I wouldn't be surprised if developments would go into
> the same direction there.

To be clear:

This requirement would only apply for 32-bit ports that are built with 
64-bit compilers. For ports that are built natively (as happens now) 
nothing would change.

So if (say) armhf would be built using 64-bit (arm64) compilers, the 
build environment for armhf would need to be able to run both the 64-bit 
and 32-bit binaries natively.

For 64-bit architectures that are built natively (like arm64), there is 
no requirement that these buildds should be able to run 32-bit binaries.

If (some of) the arm64 buildds would run on hardware that doesn't 
support 32-bit, that would obviously mean that builds for armel and 
armhf would have to be done on other hardware.

And for 32-bit architectures that are built natively, there is no 
requirement that the buildds should be able to run 64-bit binaries 
(assuming building on 32-bit still works).

I hope this clarifies what I meant.

Ivo