On Thursday, January 18, 2018 at 2:06:08 AM UTC+1, Marek Marczykowski-Górecki
wrote:
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> On Sun, Jan 14, 2018 at 03:24:04AM -0800, Vít Šesták wrote:
> > But it could be useful to use 32-bit stubdoms for those reasons. They do
> > rather I/O-bound work (=> minimal performance penalty) and they don't need
> > so much memory to utilize more than 32-bit pointers. (Also, using 32-bit
> > pointers can make a minor performance gain.)
> > …
> > It is possible to use 32-bit stubdom on a 64-bit system?
>
> That's interesting idea. Simon, what do you think about it?
>
I've tried to implement this kind of protection and I'd like to report my
failure achieve the result. Someone might be more successful. After all, I am
not much experienced with Xen internals (I mostly configure Xen through Qubes).
I've found there is a gzipped ELF with ioemu stubdom. Maybe replacing it with a
32b one could do the trick. But I am not sure if it is enough, maybe this would
just result in a 32-bit code running in 64-bit PV domain, which is not what we
want. (I am not even sure how to check it.) I haven't found any relevant
configuration where I could configure the stubdomain mode.
But I've decided to try to compile the stubdom and to try it. I've checked out
the code and switched to 4.6.6 tag. The code looks promising, some parts seem
to be ready for x86_32, despite the fact that it is no longer supported
platform for Xen itself. I however have failed the compilation itself,
regardless of the target architecture. I have tried debian-9. I needed few
additional packages to pass ./configure, that's OK. (I won't name them, because
you might miss different packages and because the error messages are pretty
clear.) There seem to be some new warnings in GCC that make the compilation to
fail, so I had to adjust tools/Rules.mk by adding line `CFLAGS +=
-Wno-misleading-indentation -Wno-unused-function`. This shifts me to another
problem: command `./configure --enable-stubdom --disable-tools --disable-xen
--disable-docs --host=x86_64 && make` results in the following error message I
am unable to resolve:
…
make -C seabios-dir all
make[6]: Entering directory '/home/user/xen/tools/firmware/seabios-dir-remote'
Compile checking out/src/stacks.o
src/stacks.c: Assembler messages:
src/stacks.c:635: Error: found '(', expected: ')'
src/stacks.c:635: Error: junk `(%ebp))' after expression
src/stacks.c:636: Warning: indirect call without `*'
…
Regards,
Vít Šesták 'v6ak'
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