From: Arnd Bergmann <arnd@arndb.de>
To: Jiri Kosina <jikos@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
        x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        "Luis R. Rodriguez" <mcgrof@kernel.org>
Subject: [PATCH 22/28] x86: apm: avoid uninitialized data
Date: Tue, 18 Oct 2016 00:16:10 +0200
Message-Id: <20161017221650.1902729-3-arnd@arndb.de>
In-Reply-To: <20161017220342.1627073-1-arnd@arndb.de>
References: <20161017220342.1627073-1-arnd@arndb.de>
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apm_bios_call() can fail, and return a status in its argument
structure. If that status however is zero during a call from
apm_get_power_status(), we end up using data that may have
never been set, as reported by "gcc -Wmaybe-uninitialized":

arch/x86/kernel/apm_32.c: In function ‘apm’:
arch/x86/kernel/apm_32.c:1729:17: error: ‘bx’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
arch/x86/kernel/apm_32.c:1835:5: error: ‘cx’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
arch/x86/kernel/apm_32.c:1730:17: note: ‘cx’ was declared here
arch/x86/kernel/apm_32.c:1842:27: error: ‘dx’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
arch/x86/kernel/apm_32.c:1731:17: note: ‘dx’ was declared here

This changes the function to return "APM_NO_ERROR" here, which
makes the code more robust to broken BIOS versions, and avoids
the warning.

Cc: x86@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/x86/kernel/apm_32.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apm_32.c b/arch/x86/kernel/apm_32.c
index c7364bd..51287cd 100644
--- a/arch/x86/kernel/apm_32.c
+++ b/arch/x86/kernel/apm_32.c
@@ -1042,8 +1042,11 @@ static int apm_get_power_status(u_short *status, u_short *bat, u_short *life)
 
 	if (apm_info.get_power_status_broken)
 		return APM_32_UNSUPPORTED;
-	if (apm_bios_call(&call))
+	if (apm_bios_call(&call)) {
+		if (!call.err)
+			return APM_NO_ERROR;
 		return call.err;
+	}
 	*status = call.ebx;
 	*bat = call.ecx;
 	if (apm_info.get_power_status_swabinminutes) {
-- 
2.9.0