On Mon, 2025-01-06 at 17:09 +0100, Ard Biesheuvel wrote: > > I suppose you're referring to > > #ifdef CONFIG_KEXEC_JUMP > /* Saved in save_processor_state. */ > movq $saved_context, %rax > lgdt saved_context_gdt_desc(%rax) > #endif > > Any reason not to simply use > > lgdt saved_context+saved_context_gdt_desc(%rip) > > here?
Because the %rip isn't what you (and the linker) think it is. This code is copied into a control page which is allocated as part of the kexec kimage. It can only access things within that same page via %rip. (Which is not as much of a restriction as it sounds, as for most of its execution the rest of the kernel isn't even present in the page tables).
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