Messages in this thread |  | | Subject | Re: [Xen-devel] [PATCH RFC] xen-block: correctly define structures in public headers | From | Ian Campbell <> | Date | Wed, 4 Dec 2013 09:28:39 +0000 |
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On Tue, 2013-12-03 at 15:11 -0500, Konrad Rzeszutek Wilk wrote: > > > If Konrad and Boris agree that breaking the kernel's ABI in this way is > > > acceptable in this specific case, I'll defer to them. > > > > My opinion as Xen on ARM hypervisor maintainer is that this is the right > > thing to do in this case. > > Heh. If somebody can guarantee me that (by testing the right variants and > mentioning this in the git commit) that this does not break x86, then > I am fine. > > And by 'break x86' I mean that this combination works: > 32-bit domU on 64-bit dom0 > 64-bit domU on 32-bit dom0 > > And perhaps also the obvious: > 64-bit domU on 64-bit dom0 > 32-bit domU on 32-bit dom0
One way to test this is with gdb on a vmlinux for each arch with CONFIG_DEBUG_INFO=y. For each MEMBER of each interesting STRUCT: (gdb) print &((struct STRUCT *)0)->MEMBER (this is effectively an open coded offsetof)
This could probably even be semi automated by producing a script to feed to gdb which run through all of the options and diffing the result.
If I could have the moon on a stick I would have a tool such as this running against the canonical Xen headers, to catch breakage as it is introduced upstream and a tool which could run against an arbitrary ELF binary to validate it against the upstream results. tools/include/xen-foreign/mkchecker.py goes some way towards that but isn't really extensible to the extent we would need/want.
While I'm asking for unicorns a gcc __attribute__((warn_on_holes)) which could be applied to a struct to enforce the need for explicit padding would probably be incredibly useful for this of thing.
> Since the xen-blkback has its own version of the structs there is no > need to change change newer and older version of it.
Someone should check that these are producing the right interface on ARM though!
> As long as that works I am OK sticking it in.
Thanks.
> I think from the ARM perspective it is still in 'experimental' phase > so anything goes to make it work under ARM.
Ian.
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