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.
Cc: Martin Sebor msebor@gcc.gnu.org Cc: stable@vger.kernel.org Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84095 Signed-off-by: Arnd Bergmann arnd@arndb.de --- arch/x86/oprofile/nmi_int.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/arch/x86/oprofile/nmi_int.c b/arch/x86/oprofile/nmi_int.c index 174c59774cc9..1d6d14db96c0 100644 --- a/arch/x86/oprofile/nmi_int.c +++ b/arch/x86/oprofile/nmi_int.c @@ -460,7 +460,7 @@ 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, @@ -470,7 +470,6 @@ static int nmi_setup(void) memcpy(per_cpu(cpu_msrs, cpu).controls, per_cpu(cpu_msrs, 0).controls, sizeof(struct op_msr) * model->num_controls); - mux_clone(cpu); }