Hi Brian, Thanks for taking a look. On Wed, 24 Apr 2024 at 19:39, Brian Gerst <brgerst@xxxxxxxxx> wrote: > > On Wed, Apr 24, 2024 at 12:06 PM Ard Biesheuvel <ardb+git@xxxxxxxxxx> wrote: > > > > From: Ard Biesheuvel <ardb@xxxxxxxxxx> > > > > The purgatory is almost entirely position independent, without any need > > for any relocation processing at load time except for the reference to > > the GDT in the entry code. Generate this reference at runtime instead, > > to remove the last R_X86_64_64 relocation from this code. > > > > While the GDT itself needs to be preserved in memory as long as it is > > live, the GDT descriptor that is used to program the GDT can be > > discarded so it can be allocated on the stack. > > > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > --- > > arch/x86/purgatory/entry64.S | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/purgatory/entry64.S b/arch/x86/purgatory/entry64.S > > index 9913877b0dbe..888661d9db9c 100644 > > --- a/arch/x86/purgatory/entry64.S > > +++ b/arch/x86/purgatory/entry64.S > > @@ -16,7 +16,11 @@ > > > > SYM_CODE_START(entry64) > > /* Setup a gdt that should be preserved */ > > - lgdt gdt(%rip) > > + leaq gdt(%rip), %rax > > + pushq %rax > > + pushw $gdt_end - gdt - 1 > > + lgdt (%rsp) > > + addq $10, %rsp > > This misaligns the stack, pushing 16 bytes on the stack but only > removing 10 (decimal). > pushw subtracts 2 from RSP and stores a word. So the total size stored is 10 decimal not 16. > > > > /* load the data segments */ > > movl $0x18, %eax /* data segment */ > > @@ -83,8 +87,8 @@ SYM_DATA_START_LOCAL(gdt) > > * 0x08 unused > > * so use them as gdt ptr > > obsolete comment > > > */ > > - .word gdt_end - gdt - 1 > > - .quad gdt > > + .word 0 > > + .quad 0 > > .word 0, 0, 0 > > This can be condensed down to: > .quad 0, 0 > This code and the comment are removed in the next patch. _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
