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From: Arnd Bergmann <arnd@arndb.de>
To: x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>
Subject: [PATCH 1/8] perf/x86: shut up false-positive -Wmaybe-uninitialized warning
Date: Wed, 19 Jul 2017 14:52:59 +0200
Message-ID: <20170719125310.2487451-2-arnd@arndb.de> (raw)
In-Reply-To: <20170719125310.2487451-1-arnd@arndb.de>

The intialization function checks for various failure scenarios, but
unfortunately the compiler gets a little confused about the possible
combinations, leading to a false-positive build warning when
-Wmaybe-uninitialized is set:

arch/x86/events/core.c: In function ‘init_hw_perf_events’:
arch/x86/events/core.c:264:3: warning: ‘reg_fail’ may be used uninitialized in this function [-Wmaybe-uninitialized]
arch/x86/events/core.c:264:3: warning: ‘val_fail’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   pr_err(FW_BUG "the BIOS has corrupted hw-PMU resources (MSR %x is %Lx)\n",

We can't actually run into this case, so this shuts up the warning
by initializing the variables to a known-invalid state.

Link: https://patchwork.kernel.org/patch/9392595/
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2: replaced original patch that reordered the code instead of
adding a fake initialization.
---
 arch/x86/events/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index ff1ea2fb9705..8e3db8f642a7 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -191,8 +191,8 @@ static void release_pmc_hardware(void) {}
 
 static bool check_hw_exists(void)
 {
-	u64 val, val_fail, val_new= ~0;
-	int i, reg, reg_fail, ret = 0;
+	u64 val, val_fail = -1, val_new= ~0;
+	int i, reg, reg_fail = -1, ret = 0;
 	int bios_fail = 0;
 	int reg_safe = -1;
 
-- 
2.9.0

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-19 12:52 [PATCH 0/8] x86: randconfig warning fixes Arnd Bergmann
2017-07-19 12:52 ` Arnd Bergmann [this message]
2017-07-20 10:24   ` [tip:x86/urgent] perf/x86: Shut up false-positive -Wmaybe-uninitialized warning tip-bot for Arnd Bergmann
2017-07-19 12:53 ` [PATCH 2/8] x86: math-emu: possible uninitialized variable use Arnd Bergmann
2017-07-20 10:25   ` [tip:x86/urgent] x86/fpu/math-emu: Fix " tip-bot for Arnd Bergmann
2017-07-19 12:53 ` [PATCH 3/8] x86: math-emu: avoid bogus -Wint-in-bool-context warning Arnd Bergmann
2017-07-20 10:25   ` [tip:x86/urgent] x86/fpu/math-emu: Avoid " tip-bot for Arnd Bergmann
2017-07-19 12:53 ` [PATCH 4/8] x86: io: add "memory" clobber to insb/insw/insl/outsb/outsw/outsl Arnd Bergmann
2017-07-19 19:25   ` Arnd Bergmann
2017-07-19 19:46   ` Linus Torvalds
2017-07-20 10:25   ` [tip:x86/urgent] x86/io: Add " tip-bot for Arnd Bergmann
2017-07-19 12:53 ` [PATCH 5/8] x86: silence build with "make -s" Arnd Bergmann
2017-07-20 10:26   ` [tip:x86/urgent] x86/build: Silence the " tip-bot for Arnd Bergmann
2017-07-19 12:53 ` [PATCH 6/8] x86: add MULTIUSER dependency for KVM Arnd Bergmann
2017-07-19 14:11   ` Radim Krčmář
2017-07-19 14:18     ` Arnd Bergmann
2017-07-19 16:13       ` Radim Krčmář
2017-07-23 13:41         ` Paolo Bonzini
2017-07-19 12:53 ` [PATCH 7/8] x86: add PCI dependency for PUNIT_ATOM_DEBUG Arnd Bergmann
2017-07-20 10:26   ` [tip:x86/urgent] x86/platform: Add " tip-bot for Arnd Bergmann
2017-07-19 12:53 ` [PATCH 8/8] x86: intel-mid: fix a format string overflow warning Arnd Bergmann
2017-07-20 10:27   ` [tip:x86/urgent] x86/platform/intel-mid: Fix " tip-bot for Arnd Bergmann

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