linux-kernel - [4.4-stable 15/22] perf/x86: Shut up false-positive -Wmaybe-uninitialized warning

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Date:   Tue, 20 Feb 2018 12:55:02 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     stable@...r.kernel.org
Cc:     Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: [4.4-stable 15/22] perf/x86: Shut up false-positive -Wmaybe-uninitialized warning

commit 11d8b05855f3749bcb6c57e2c4052921b9605c77 upstream.

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.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20170719125310.2487451-2-arnd@arndb.de
Link: https://patchwork.kernel.org/patch/9392595/
Signed-off-by: Ingo Molnar <mingo@...nel.org>
[arnd: rebased to 4.4]
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/x86/kernel/cpu/perf_event.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 5b2f2306fbcc..b52a8d08ab36 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -188,8 +188,8 @@ 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