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    Subject[PATCH 3.16 275/410] x86/oprofile: Fix bogus GCC-8 warning in nmi_setup()
    3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Arnd Bergmann <arnd@arndb.de>

    commit 85c615eb52222bc5fab6c7190d146bc59fac289e upstream.

    GCC-8 shows a warning for the x86 oprofile code that copies per-CPU
    data from CPU 0 to all other CPUs, which when building a non-SMP
    kernel turns into a memcpy() with identical source and destination
    pointers:

    arch/x86/oprofile/nmi_int.c: In function 'mux_clone':
    arch/x86/oprofile/nmi_int.c:285:2: error: 'memcpy' source argument is the same as destination [-Werror=restrict]
    memcpy(per_cpu(cpu_msrs, cpu).multiplex,
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    per_cpu(cpu_msrs, 0).multiplex,
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    sizeof(struct op_msr) * model->num_virt_counters);
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    arch/x86/oprofile/nmi_int.c: In function 'nmi_setup':
    arch/x86/oprofile/nmi_int.c:466:3: error: 'memcpy' source argument is the same as destination [-Werror=restrict]
    arch/x86/oprofile/nmi_int.c:470:3: error: 'memcpy' source argument is the same as destination [-Werror=restrict]

    I have analyzed a number of such warnings now: some are valid and the
    GCC warning is welcome. Others turned out to be false-positives, and
    GCC was changed to not warn about those any more. This is a corner case
    that is a false-positive but the GCC developers feel it's better to keep
    warning about it.

    In this case, it seems best to work around it by telling GCC
    a little more clearly that this code path is never hit with
    an IS_ENABLED() configuration check.

    Cc:stable as we also want old kernels to build cleanly with GCC-8.

    Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    Cc: Jessica Yu <jeyu@kernel.org>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Martin Sebor <msebor@gcc.gnu.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Robert Richter <rric@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: oprofile-list@lists.sf.net
    Link: http://lkml.kernel.org/r/20180220205826.2008875-1-arnd@arndb.de
    Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84095
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    arch/x86/oprofile/nmi_int.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/x86/oprofile/nmi_int.c
    +++ b/arch/x86/oprofile/nmi_int.c
    @@ -471,7 +471,7 @@ static int nmi_setup(void)
    goto fail;

    for_each_possible_cpu(cpu) {
    - if (!cpu)
    + if (!IS_ENABLED(CONFIG_SMP) || !cpu)
    continue;

    memcpy(per_cpu(cpu_msrs, cpu).counters,
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