• Arnd Bergmann's avatar
    x86/oprofile: Fix bogus GCC-8 warning in nmi_setup() · 7a14562d
    Arnd Bergmann authored
    commit 85c615eb 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: default avatarArnd 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
    Cc: stable@vger.kernel.org
    Link: http://lkml.kernel.org/r/20180220205826.2008875-1-arnd@arndb.de
    Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84095Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    7a14562d
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