linux-kernel - [PATCH 1/2] rtc: cmos: Fix non-ACPI undefined reference to `hpet_rtc

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Date:   Tue, 2 Oct 2018 02:08:49 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...ux-mips.org>
To:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
cc:     linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH 1/2] rtc: cmos: Fix non-ACPI undefined reference to
 `hpet_rtc_interrupt'

Fix a commit 311ee9c151ad ("rtc: cmos: allow using ACPI for RTC alarm 
instead of HPET") `rtc-cmos' regression causing a link error:

drivers/rtc/rtc-cmos.o: In function `cmos_platform_probe':
rtc-cmos.c:(.init.text+0x33c): undefined reference to `hpet_rtc_interrupt'
rtc-cmos.c:(.init.text+0x3f4): undefined reference to `hpet_rtc_interrupt'

with non-ACPI platforms using this driver.  The cause is the change of 
the condition guarding the use of `hpet_rtc_interrupt'.

Previously it was a call to `is_hpet_enabled'.  That function is static 
inline and has a hardcoded 0 result for non-ACPI platforms, which imply 
!HPET_EMULATE_RTC.  Consequently the compiler optimized the whole block 
away including the reference to `hpet_rtc_interrupt', which never made 
it to the link stage.

Now the guarding condition is a call to `use_hpet_alarm', which is not 
static inline and therefore the compiler may not be able to prove that 
it actually always returns 0 for non-ACPI platforms.  Consequently the 
build breaks with an unsatisfied reference, because `hpet_rtc_interrupt' 
is nowhere defined at link time.

Fix the problem by marking `use_hpet_alarm' inline.  As the `inline' 
keyword serves as an optimization hint rather than a requirement the 
compiler is still free to choose whether inlining will be beneficial or 
not for ACPI platforms.

Signed-off-by: Maciej W. Rozycki <macro@...ux-mips.org>
Fixes: 311ee9c151ad ("rtc: cmos: allow using ACPI for RTC alarm instead of HPET")
Cc: stable@...r.kernel.org # 4.18+
---
 drivers/rtc/rtc-cmos.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

linux-rtc-cmos-use-hpet-alarm-inline.diff
Index: linux-20180812-4maxp64/drivers/rtc/rtc-cmos.c
===================================================================
--- linux-20180812-4maxp64.orig/drivers/rtc/rtc-cmos.c
+++ linux-20180812-4maxp64/drivers/rtc/rtc-cmos.c
@@ -167,7 +167,7 @@ static inline int hpet_unregister_irq_ha
 #endif

 /* Don't use HPET for RTC Alarm event if ACPI Fixed event is used */
-static int use_hpet_alarm(void)
+static inline int use_hpet_alarm(void)
 {
 	return is_hpet_enabled() && !use_acpi_alarm;
 }