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Re: [PATCH] x86/PV: ignore PAE_MODE ELF note for 64-bit Dom0
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 15 Feb 2023 18:41:25 +0000
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- Cc: Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15/02/2023 3:10 pm, Jan Beulich wrote:
> Besides a printk() the main effect is slight corruption of the start
> info magic: While that's meant to be xen-3.0-x86_64, it wrongly ended
> up as xen-3.0-x86_64p.
>
> Fixes: 460060f83d41 ("libelf: use for x86 dom0 builder")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> RFC: While Linux works fine with the adjustment, I'm not entirely
> certain of external tools (kexec?) having grown a dependency.
Again, I wonder why you think regular kexec has any anything to do with
this?
Are you mixing it up with (legacy) pvgrub which does end up doing a
kexec inside the context of a PV guest? If so, it's MiniOS's support
you need to care about, and I cant see any logic that even inspects the
start_info->magic[] (either in MiniOS itself, or the pvgrub patches).
Like plenty of other fields in the undocumented PV ABI, it's not
interesting at all to software. There's nothing I can see in it that
you don't know at compile time.
> It
> may be worth noting that XenoLinux and its forward ports never had
> this ELF note in 64-bit kernels, so in principle it may be
> reasonable to expect that no such dependency exists anywhere.
NetBSD sets PAE_MODE for 32bit and 64bit but, like everything else,
doesn't appear to inspect start_info->magic[].
xen-3.0-x86_64p is obviously bogus. I find it far more likely that
noone has ever noticed this bug, than anyone gaining a dependency on it.
Insert usual rant about the PV ABI being entirely undocumented...
~Andrew
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