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    SubjectRe: [PATCH v3 7/8] powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI
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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>

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