Frediano Ziglio e58a2858d5 x86/boot: Preserve the value clobbered by the load-base calculation ...

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: 1695e53851 ("x86/boot: Fix the boot time relocation calculations")
Fixes: d96bb172e8 ("x86/entry: Early PVH boot code")
Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

2024-08-27 18:08:19 +01:00

..

how-xen-boots.rst

x86/boot: Preserve the value clobbered by the load-base calculation

2024-08-27 18:08:19 +01:00

index.rst

docs/sphinx: How Xen Boots on x86

2019-12-10 17:23:39 +00:00