Re: [Xen-devel] What is tools/firmware/rombios/32bit/... used for?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-07-28 at 23:58 +0100, Andrew Cooper wrote:
> On 28/07/2014 22:14, Anthony Wright wrote:
> > I'm trying to build xen on a pure 64 bit system, but the build is
> > failing when it tries to build
> > tools/firmware/rombios/32bit/tcgbios/tcgbios.c with the error:
> >
> > /usr/include/gnu/stubs.h:7:27: fatal error: gnu/stubs-32.h: No such file
> > or directory
> >
> > From reading around the error, it's caused by a lack of a 32 bit libc
> > which would make sense as I only have a 64 bit libc on the system at the
> > moment. To reduce the size of the distro (see my earlier Perl dependency
> > post), I'd prefer to avoid having to build a 32 bit libc. I therefore
> > wondered what tcgbios does and what the impact of failing to build the
> > 32 bit support for it would be?
> >
> > thanks,
> >
> > Anthony.
> 
> hvmloader is a 32bit binary.  It is the first bit of code executed in
> any HVM domain and has the job of preparing certain architectural bits
> for the BIOS, followed by dropping into 16bit mode to execute the
> provided BIOS image.  Irrespective of the rest of your install, it does
> have to be built as a 32bit ELF file, as 32bit is the start mode of HVM
> domains.
> 
> There is no way of avoiding the need for a 32bit set of headers if you
> want to build the base components Xen needs to function.

Note that this is a build time requirement only, I think. The final
hvmloader binary is essentially statically linked and can be deployed
onto a system without any 32bit headers/libc/etc present.

To answer the original question /rombios/32bit is the parts of the
ROMBIOS bios which run in 32-bit mode (the BIOS will thunk from 16-
to/from 32-bit mode as necessary for various things). ROMBIOS is used
with qemu-xen-traditional only so removing it will mean you can't use
that. The header requirement for this is also build time only.

Ian.


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