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Date: Wed, 03 Aug 2016 14:46:49 +1000
From: Michael Ellerman <>
To: Kees Cook <>
Cc: "kernel-hardening\" <>, Arnd Bergmann <>, Greg Kroah-Hartman <>, Andrew Morton <>, "David S. Miller" <>, Mauro Carvalho Chehab <>, Jiri Slaby <>, Guenter Roeck <>, LKML <>, "linuxppc-dev\" <>, Anton Blanchard <>, Alan Modra <>
Subject: Re: Re: Linker segfault on powerpc when CONFIG_LKDTM=y (was Re: [PATCH 3/5] lkdtm: add function for testing .rodata section)

Kees Cook <> writes:
> On Mon, Aug 1, 2016 at 8:12 PM, Michael Ellerman <> wrote:
>> Kees Cook <> writes:
>>> On Mon, Aug 1, 2016 at 5:37 AM, Michael Ellerman <> wrote:
>>>>   scripts/ line 52: 36260 Segmentation fault      (core dumped) ${LD} ${LDFLAGS} ${LDFLAGS_vmlinux} -o ${2} -T ${lds} ${KBUILD_VMLINUX_INIT} --start-group ${KBUILD_VMLINUX_MAIN} --end-group ${1}
>>>> Haven't had a chance to debug it further.
>> Interestingly I *can't* reproduce with the Ubuntu x86->ppc cross
>> (5.4.0-6ubuntu1~16.04.1).
> Oh, weird. Well, that does explains my lack of hitting the problem,
> though: that's the cross compiler I was using. :P

Actually that was a false negative.

The trick is you have to have LKDTM=y *and* FUNCTION_TRACER=y.

It is a linker bug:

Which Alan has already fixed.

But we need to workaround existing linkers that are out there.

We can do that by marking lkdtm_rodata_do_nothing() notrace, which I
think makes sense for all arches actually.

So I'll send you a patch to do that.


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