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Re: [PATCH v3] x86/boot: Preserve the value clobbered by the load-base calculation
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Fri, 23 Aug 2024 10:40:50 -0400
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- Cc: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Fri, 23 Aug 2024 14:41:05 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2024-08-23 09:10, Andrew Cooper wrote:
From: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
Right now, Xen clobbers the value at 0xffc when performing it's load-base
calculation. We've got plenty of free registers at this point, so the value
can be preserved easily.
This fixes a real bug booting under Coreboot+SeaBIOS, where 0xffc happens to
be the cbmem pointer (e.g. Coreboot's dmesg ring, among other things).
However, there's also a better choice of memory location to use than 0xffc, as
all our supported boot protocols have a pointer to an info structure in %ebx.
Update the documentation to match.
Fixes: 1695e53851e5 ("x86/boot: Fix the boot time relocation calculations")
Fixes: d96bb172e8c9 ("x86/entry: Early PVH boot code")
Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
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