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Date:   Fri, 12 May 2017 00:20:14 -0700
From:   Jessica Yu <jeyu@...hat.com>
To:     Michael Ellerman <mpe@...erman.id.au>
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

+++ 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>

>---
> arch/powerpc/include/asm/module.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
>diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
>index 53885512b8d3..6c0132c7212f 100644
>--- a/arch/powerpc/include/asm/module.h
>+++ b/arch/powerpc/include/asm/module.h
>@@ -14,6 +14,10 @@
> #include <asm-generic/module.h>
>
>
>+#ifdef CC_USING_MPROFILE_KERNEL
>+#define MODULE_ARCH_VERMAGIC	"mprofile-kernel"
>+#endif
>+
> #ifndef __powerpc64__
> /*
>  * Thanks to Paul M for explaining this.
>-- 
>2.7.4
>

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