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Re: A 48 byte kernel module/cfi load mystery
- From: Mark Wielaard <mjw at redhat dot com>
- To: roland at redhat dot com
- Cc: systemtap at sourceware dot org
- Date: Fri, 02 Jul 2010 16:14:36 +0200
- Subject: Re: A 48 byte kernel module/cfi load mystery
- References: <1278069785.4626.29.camel@springer.wildebeest.org>
On Fri, 2010-07-02 at 13:23 +0200, Mark Wielaard wrote:
> I cannot figure out why the FDE initial_location is shifted by 48 bytes.
> If in the stap unwinder I just pretend the kernel module has been loaded
> a little earlier:
>
> - vm_addr = s->static_addr;
> + vm_addr = s->static_addr - 0x30;
>
> all the CFIs line up and I can unwind perfectly through the kernel
> modules. But this mysterious magic 48 bytes bothers me. It is the same
> on i686 btw. Any idea where they might be coming from?
Actually it isn't always the same. It was for that kernel on both x86_64
and i686. But with a recent fedora x86_64 kernel
(2.6.33.5-124.fc13.x86_64) the offset is always 0x24.
Cheers,
Mark