linux/arch/x86/oprofile
Arnd Bergmann 85c615eb52 x86/oprofile: Fix bogus GCC-8 warning in nmi_setup()
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
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=84095
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-21 09:54:17 +01:00
..
backtrace.c oprofile/x86: Convert x86_backtrace() to use the new unwinder 2016-09-20 08:29:34 +02:00
init.c oprofile, x86: Reimplement nmi timer mode using perf event 2011-11-04 16:27:18 +01:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
nmi_int.c x86/oprofile: Fix bogus GCC-8 warning in nmi_setup() 2018-02-21 09:54:17 +01:00
op_counter.h oprofile, x86: Allow setting EDGE/INV/CMASK for counter events 2011-03-24 18:45:44 +01:00
op_model_amd.c x86/cpufeature: Carve out X86_FEATURE_* 2016-01-30 11:22:17 +01:00
op_model_p4.c percpu: Resolve ambiguities in __get_cpu_var/cpumask_var_t 2014-08-28 08:58:57 -04:00
op_model_ppro.c x86/oprofile/ppro: Do not use __this_cpu*() in preemptible context 2017-11-08 13:01:54 +01:00
op_x86_model.h perf, x86: Implement IBS initialization 2011-10-10 06:57:16 +02:00