Messages in this thread | | | Date | Mon, 24 Dec 2012 15:56:35 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH v7 00/27] x86, boot, 64bit: Add support for loading ramdisk and bzImage above 4G |
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On 12/23/2012 10:00 AM, Yinghai Lu wrote: > On Sun, Dec 23, 2012 at 6:33 AM, H. Peter Anvin <hpa@zytor.com> wrote: >> Explanation please? >> > > you have following change in the patch > > /* Finally jump to run C code and to be on real kernel address > * Since we are running on identity-mapped space we have to jump > * to the full 64bit address, this is only possible as indirect > * jump. In addition we need to ensure %cs is set so we make this > - * a far return. > + * a far jump. > */ > - movq initial_code(%rip),%rax > pushq $0 # fake return address to stop unwinder > - pushq $__KERNEL_CS # set correct cs > - pushq %rax # target address in negative space > - lretq > + /* gas 2.22 is buggy and mis-assembles ljmpq */ > + rex64 ljmp *initial_code(%rip) > > #ifdef CONFIG_HOTPLUG_CPU > /* > > remove that change, AMD systems works again. >
That is not an explanation.
-hpa
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