4.4-stable review patch. If anyone has any objections, please let me know.
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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 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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,