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Re: [PATCH 2/3] x86/kexec: Simplify the relocation of compat_mode_gdt_desc
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 21 Feb 2023 11:48:14 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 21 Feb 2023 10:48:34 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.02.2023 18:48, Andrew Cooper wrote:
> Assemble the GDT base relative to kexec_reloc, and simply add the identity map
> base address to relocate.
>
> Adjust a stale comment, and drop the unused matching label.
Only kind of - the comment is referencing call_32_bit, and hence wasn't
really stale. And what was (and would remain to be) dead is call_64_bit.
May want slightly re-wording.
> @@ -81,9 +80,8 @@ ENTRY(kexec_reloc)
> /* Setup IDT. */
> lidt compat_mode_idt(%rip)
>
> - /* Load compat GDT. */
> - leaq compat_mode_gdt(%rip), %rax
> - movq %rax, (compat_mode_gdt_desc + 2)(%rip)
> + /* Relocate and load compat GDT. */
> + add %rdi, 2 + compat_mode_gdt_desc(%rip)
> lgdt compat_mode_gdt_desc(%rip)
Where's %rdi being populated for this? At kexec_reloc %rdi points at
the code page, but prior to calling relocate_pages the register is
overwritten (and the original value is lost). relocate_pages also
has normal C calling convention afaict; kind of as a result %rdi is
actually being clobbered there.
Jan
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