Subject: Re: [PATCH v3 7/8] powerpc/ftrace: Add support for -mprofile-kernel
 ftrace ABI
To: Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@ozlabs.org
References: <1456979220-10931-1-git-send-email-mpe@ellerman.id.au>
 <1456979220-10931-7-git-send-email-mpe@ellerman.id.au>
Cc: duwe@lst.de, linux-kernel@vger.kernel.org, rostedt@goodmis.org,
        kamalesh@linux.vnet.ibm.com, pmladek@suse.com, jeyu@redhat.com,
        jkosina@suse.cz, live-patching@vger.kernel.org, mbenes@suse.cz
From: Balbir Singh <bsingharora@gmail.com>
Message-ID: <56D8EBA4.5090807@gmail.com>
Date: Fri, 4 Mar 2016 12:57:56 +1100
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On 03/03/16 15:26, Michael Ellerman wrote:
> From: Torsten Duwe <duwe@suse.de>
>
> The gcc switch -mprofile-kernel defines a new ABI for calling _mcount()
> very early in the function with minimal overhead.
>
> Although mprofile-kernel has been available since GCC 3.4, there were
> bugs which were only fixed recently. Currently it is known to work in
> GCC 4.9, 5 and 6.
>
> Additionally there are two possible code sequences generated by the
> flag, the first uses mflr/std/bl and the second is optimised to omit the
> std. Currently only gcc 6 has the optimised sequence. This patch
> supports both sequences.
>
> Initial work started by Vojtech Pavlik, used with permission.
>
> Key changes:
>  - rework _mcount() to work for both the old and new ABIs.
>  - implement new versions of ftrace_caller() and ftrace_graph_caller()
>    which deal with the new ABI.
>  - updates to __ftrace_make_nop() to recognise the new mcount calling
>    sequence.
>  - updates to __ftrace_make_call() to recognise the nop'ed sequence.
>  - implement ftrace_modify_call().
>  - updates to the module loader to surpress the toc save in the module
>    stub when calling mcount with the new ABI.
>
> Signed-off-by: Torsten Duwe <duwe@suse.de>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>