On Mon, 6 Jul 2009 05:12:51 pm Jan Beulich wrote:
> >Jan Beulich napsal(a):
> >> Since these CRCs are really only 32-bit quantities, there's no need to
> >> store them in 64-bit slots. Since, however, gcc doesn't allow
> >> respective initializations, asm() constructs get used to create the CRC
> >> tables (and its for that reason that the patch only makes x86-64 and
> >> ia64 utilize that functionality, as I can't verify this doesn't break
> >> in some subtle way elsewhere).
> >
> >...
> >
> >> struct modversion_info
> >> {
> >> - unsigned long crc;
> >> + ksym_crc_t crc;
> >> char name[MODULE_NAME_LEN];
> >> };
> >
> >This change breaks module-init-tools:
> >Before:
> >$ /sbin/modprobe --dump-modversions _build/drivers/usb/core/usbcore.ko
> >
> >| head
> >
> >0xb49b735a module_layout
> >0xdb7e6a70 bus_register
> >...
> >After:
> >$ /sbin/modprobe --dump-modversions
> >_build-crc-int/drivers/usb/core/usbcore.ko | head
> >0x75646f6d91ea7b5c le_layout
> >0x5f7375623e215f43 register
> >...
> >It also breaks the newly added depmod -E option (check symbol versions),
> >which also reads the struct modversion_info array (*). Is it possible
> >name the section differently (__versions2?) on those architectures where
> >the size changes, so that it is possible to fix m-i-t in a
> >backwards-compatible manner?
>
> First of all I'd view it as a design bug if user mode code assumptions
> prevent changes to the kernel.
Yes, but unfortunately it happens. We do it much less than we used to, but
there are limits.
> But taking this as an uncorrectable fact, I'd think that renaming the
> section would certainly be an option (though I'm unsure whether that would
> have other consequences - Rusty?), however I could also imagine other means
> to communicate to user land the width of a CRC value (e.g. adding an
> absolute symbol during the .ko linking stage).
No, just break it once. And I still like the idea that we should do something
more radical if we're going to break this anyway, rather than these nasty asm
hacks.
Thanks,
Rusty.
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