I mean that if, say, GRUB fails to read reiserfs, I'd like to be
able to reproduce the problem in grub-fstest even if I'm compiling
it on x86_64.
In this case, so we're producing a 32-bit, pc grub image. To have a
similar effect in grub-fstest, we'd need to define grub_size_t to be a
32-bit quantity when compiling that too, am I right? Is there any
reason not to just have grub-fstest try to imitate whatever the
bootloader image decides it needs? So if some platform requires a
64-bit bootloader and we're running on 32-bits, we may need a 64-bit
grub_size_t in both places (well, this is maybe not likely to work
entirely, but GCC can generate the operations -- or we could just use
32 bit for grub-fstest then if we think it's the least-nonsensical
thing to do in that hypothetical situation).