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Date:   Mon, 15 May 2017 19:24:58 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Jessica Yu <jeyu@...hat.com>
Cc:     linuxppc-dev@...abs.org, rusty@...tcorp.com.au,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/modules: If mprofile-kernel is enabled add it to vermagic

Jessica Yu <jeyu@...hat.com> writes:

> +++ Michael Ellerman [10/05/17 16:57 +1000]:
>>On powerpc we can build the kernel with two different ABIs for mcount(), which
>>is used by ftrace. Kernels built with one ABI do not know how to load modules
>>built with the other ABI. The new style ABI is called "mprofile-kernel", for
>>want of a better name.
>>
>>Currently if we build a module using the old style ABI, and the kernel with
>>mprofile-kernel, when we load the module we'll oops something like:
>>
>>  # insmod autofs4-no-mprofile-kernel.ko
>>  ftrace-powerpc: Unexpected instruction f8810028 around bl _mcount
>>  ------------[ cut here ]------------
>>  WARNING: CPU: 6 PID: 3759 at ../kernel/trace/ftrace.c:2024 ftrace_bug+0x2b8/0x3c0
>>  CPU: 6 PID: 3759 Comm: insmod Not tainted 4.11.0-rc3-gcc-5.4.1-00017-g5a61ef74f269 #11
>>  ...
>>  NIP [c0000000001eaa48] ftrace_bug+0x2b8/0x3c0
>>  LR [c0000000001eaff8] ftrace_process_locs+0x4a8/0x590
>>  Call Trace:
>>    alloc_pages_current+0xc4/0x1d0 (unreliable)
>>    ftrace_process_locs+0x4a8/0x590
>>    load_module+0x1c8c/0x28f0
>>    SyS_finit_module+0x110/0x140
>>    system_call+0x38/0xfc
>>  ...
>>  ftrace failed to modify
>>  [<d000000002a31024>] 0xd000000002a31024
>>   actual:   35:65:00:48
>>
>>We can avoid this by including in the vermagic whether the kernel/module was
>>built with mprofile-kernel. Which results in:
>>
>>  # insmod autofs4-pg.ko
>>  autofs4: version magic
>>  '4.11.0-rc3-gcc-5.4.1-00017-g5a61ef74f269 SMP mod_unload modversions '
>>  should be
>>  '4.11.0-rc3-gcc-5.4.1-00017-g5a61ef74f269-dirty SMP mod_unload modversions mprofile-kernel'
>>  insmod: ERROR: could not insert module autofs4-pg.ko: Invalid module format
>>
>>Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
>
> Looks good to me:
>
> Acked-by: Jessica Yu <jeyu@...hat.com>

Thanks.

cheers

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