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@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84095
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
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);
}
--
2.9.0