linux-kernel - Re: [v4.2] powerpc/modules: Don't try to restore r2 after a sibling call

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Message-Id: <3ywyXY71NTz9t3m@ozlabs.org>
Date:   Tue, 12 Dec 2017 22:39:25 +1100 (AEDT)
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        live-patching@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [v4.2] powerpc/modules: Don't try to restore r2 after a sibling call

On Thu, 2017-11-16 at 17:45:37 UTC, Josh Poimboeuf wrote:
> 
> From: Josh Poimboeuf <jpoimboe@...hat.com>
> Subject: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call
> 
> When attempting to load a livepatch module, I got the following error:
> 
>   module_64: patch_module: Expect noop after relocate, got 3c820000
> 
> The error was triggered by the following code in
> unregister_netdevice_queue():
> 
>   14c:   00 00 00 48     b       14c <unregister_netdevice_queue+0x14c>
>                          14c: R_PPC64_REL24      net_set_todo
>   150:   00 00 82 3c     addis   r4,r2,0
> 
> GCC didn't insert a nop after the branch to net_set_todo() because it's
> a sibling call, so it never returns.  The nop isn't needed after the
> branch in that case.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Acked-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/b9eab08d012fa093947b230f9a8725

cheers