Patch "x86/oprofile: Fix bogus GCC-8 warning in nmi_setup()" has been added to the 4.4-stable tree

Patch "x86/oprofile: Fix bogus GCC-8 warning in nmi_setup()" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    x86/oprofile: Fix bogus GCC-8 warning in nmi_setup()

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-oprofile-fix-bogus-gcc-8-warning-in-nmi_setup.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 85c615eb52222bc5fab6c7190d146bc59fac289e Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@arndb.de>
Date: Tue, 20 Feb 2018 21:58:21 +0100
Subject: x86/oprofile: Fix bogus GCC-8 warning in nmi_setup()

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,


Patches currently in stable-queue which might be from arnd@arndb.de are

queue-4.4/x86-oprofile-fix-bogus-gcc-8-warning-in-nmi_setup.patch
queue-4.4/cfg80211-fix-cfg80211_beacon_dup.patch