running 64-bit binaries on a 32-bit OS

[Yann E. MORIN]

Hello Robert and all!

On Tuesday 24 April 2007 19:52, Robert P. J. Day wrote:
>   AFAIK, i can build a 64-bit toolchain, then compile a simple "hello,
> world" using that, right?  i can't just run a 64-bit binary on the
> 32-bit OS, so testing a 64-bit binary would truly show that the
> toolchain was built correctly, right?  with all of the libs properly
> built and so on.

On your 32-bit distro, build your "hello, world!" demo app with your 64-bit
cross-toolchain. A static link should be enough, while a dynamic link would be
more complex to set up.
Run your demo app: it doesn't run.
Then build a 64-bit enabled kernel with 32-bit (IA32) emulation.
Boot this 64-bit kernel. Your userland is still 32-bit, but your kernel should
just handle this.
Then run your demo app: it runs.

Plus, as already suggested, file and readelf to check the demo app.

That's what I'd do.

Note: simply booting the kernel is not a sufficient proof, because one could
argue that it is still 32-bit because it runs the 32-bit userland. By running
your 64-bit demo app with your 64-bit kernel, you can proove the 64-bitness
of your toolchain. Somewhat.

Regards,
Yann E. MORIN.

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