On Tue, 2024-12-17 at 10:25 +0100, Ard Biesheuvel wrote: > > > > You can still avoid the absolute relocations though, ... > > ... > > > > + addq $identity_mapped, %rsi > > > > + subq $__relocate_kernel_start, %rsi > > > > > > ... if you turn this into > > > > > > 0: addq $identity_mapped - 0b, %rsi > > > subq $__relocate_kernel_start - 0b, %rsi > > > > Is there any benefit to doing so? Are absolute relocations problematic? > > Every absolute relocation produces an entry in the relocation table > that needs to be applied at every boot when KASLR is in effect. Beyond > that, it doesn't matter. > > I've looked into PIC codegen/PIE linking for the core kernel, which is > why this caught my eye. If that effort ever advances, I'll need to > revisit this code as well and apply the change I suggested. OK, since it looks like I'll be reposting this series once I'm back at a keyboard for real, I've done that in my tree. There's one more absolute relocation, for saved_context just before returning to the kernel from the 'virtual_mapped' code. That's only reloading the GDT, and we could probably do that from the C code in machine_kexec().
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