linux-kernel - [tip:x86/urgent] perf/x86: Shut up false-positive -Wmaybe-uninitialized warning

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Message-ID: <tip-11d8b05855f3749bcb6c57e2c4052921b9605c77@git.kernel.org>
Date:   Thu, 20 Jul 2017 03:24:45 -0700
From:   tip-bot for Arnd Bergmann <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, jpoimboe@...hat.com,
        alexander.shishkin@...ux.intel.com, acme@...nel.org, arnd@...db.de,
        mingo@...nel.org, torvalds@...ux-foundation.org, luto@...nel.org,
        hpa@...or.com, tglx@...utronix.de, peterz@...radead.org
Subject: [tip:x86/urgent] perf/x86: Shut up false-positive
 -Wmaybe-uninitialized warning

Commit-ID:  11d8b05855f3749bcb6c57e2c4052921b9605c77
Gitweb:     http://git.kernel.org/tip/11d8b05855f3749bcb6c57e2c4052921b9605c77
Author:     Arnd Bergmann <arnd@...db.de>
AuthorDate: Wed, 19 Jul 2017 14:52:59 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 20 Jul 2017 10:46:23 +0200

perf/x86: Shut up false-positive -Wmaybe-uninitialized warning

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>
---
 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 ff1ea2f..8e3db8f 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;