[PATCH 22/28] x86: apm: avoid uninitialized data

Arnd Bergmann
2016-10-17T22:19:48Z

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