Messages in this thread | | | Date | Fri, 14 Mar 2008 09:31:38 -0700 | From | Arjan van de Ven <> | Subject | Re: 2.6.22.6 - Discrepancy between running and on-disk kernels |
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On Fri, 14 Mar 2008 12:08:16 -0400 Yan <rottled@gmail.com> wrote:
> Can you point me to where in the source that self-patching happens? I > tried grep'ing > through the source for anything relevant, and came out empty handed.
in the apply_alternatives() function
> > -yan > > On Fri, Mar 14, 2008 at 12:00 PM, Arjan van de Ven > <arjan@infradead.org> wrote: > > On Fri, 14 Mar 2008 10:51:43 -0400 > > Yan <rottled@gmail.com> wrote: > > > > > Hello, > > > > > > I have been trying to compare the code from the on-disk > > > compressed kernel that was booted and the running kernel > > > extracted from /dev/kmem. I extracted the kernel's code from the > > > disk image by stripping the head.S and similar and gunzipping > > > it, and extracted the kernel from /dev/kmem by reading data > > > between _text and _etext symbol offsets. > > > > > > I then ran both through a disassembler and diff'ed the outputs. > > > Predictably, the disassembly was similar, but not identical. Some > > > instructions (e.g. bts) had a 'lock' prefix, where as others had > > > a 'nop' in its place. > > > > > > There were other differences with some instructions like mfence. > > > Everything else matched just fine, the differences were mostly in > > > memory-referencing instructions. > > > > > > My question is, what can be changing the kernel between being on > > > static storage and being loaded? > > > > the kernel code is self-patching, it gets modified to match your > > system during boot time. So you cannot assume that the kernel on > > disk and the kernel in memory are identical. > > (Same goes for modules) > >
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