linux-kernel - [PATCH] staging: rtl8723bs: Fix build error with Clang when inlining is disabled

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Message-Id: <20190116060302.8882-1-natechancellor@gmail.com>
Date:   Tue, 15 Jan 2019 23:03:02 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] staging: rtl8723bs: Fix build error with Clang when inlining is disabled

When CONFIG_NO_AUTO_INLINE was present in linux-next (which added
'-fno-inline-functions' to KBUILD_CFLAGS), an allyesconfig build with
Clang failed at the modpost stage:

ERROR: "is_broadcast_mac_addr" [drivers/staging/rtl8723bs/r8723bs.ko] undefined!
ERROR: "is_zero_mac_addr" [drivers/staging/rtl8723bs/r8723bs.ko] undefined!
ERROR: "is_multicast_mac_addr" [drivers/staging/rtl8723bs/r8723bs.ko] undefined!

These functions were marked as extern inline, meaning that if inlining
doesn't happen, the function will be undefined, as it is above.

This happens to work with GCC because the '-fno-inline-functions' option
respects the __inline attribute so all instances of these functions are
inlined as expected and the definition doesn't actually matter. However,
with Clang and '-fno-inline-functions', a function has to be marked with
the __always_inline attribute to be considered for inlining, which none
of these functions are. Clang tries to find the symbol definition
elsewhere as it was told and fails, which trickles down to modpost.

To make sure that this code compiles regardless of compiler and make the
intention of the code clearer, use 'static __always_inline' to ensure
that these functions are always inlined. Some alternative solutions
included 'extern __always_inline' or converting these functions to
macros (so the preprocessor deals with them) but I would argue this is
the more "standard" solution.

Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---
 drivers/staging/rtl8723bs/include/ieee80211.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/rtl8723bs/include/ieee80211.h b/drivers/staging/rtl8723bs/include/ieee80211.h
index bcc8dfa8e672..959e822315b5 100644
--- a/drivers/staging/rtl8723bs/include/ieee80211.h
+++ b/drivers/staging/rtl8723bs/include/ieee80211.h
@@ -850,18 +850,18 @@ enum ieee80211_state {
 #define IP_FMT "%pI4"
 #define IP_ARG(x) (x)

-extern __inline int is_multicast_mac_addr(const u8 *addr)
+static __always_inline int is_multicast_mac_addr(const u8 *addr)
 {
         return ((addr[0] != 0xff) && (0x01 & addr[0]));
 }

-extern __inline int is_broadcast_mac_addr(const u8 *addr)
+static __always_inline int is_broadcast_mac_addr(const u8 *addr)
 {
 	return ((addr[0] == 0xff) && (addr[1] == 0xff) && (addr[2] == 0xff) &&   \
 		(addr[3] == 0xff) && (addr[4] == 0xff) && (addr[5] == 0xff));
 }

-extern __inline int is_zero_mac_addr(const u8 *addr)
+static __always_inline int is_zero_mac_addr(const u8 *addr)
 {
 	return ((addr[0] == 0x00) && (addr[1] == 0x00) && (addr[2] == 0x00) &&   \
 		(addr[3] == 0x00) && (addr[4] == 0x00) && (addr[5] == 0x00));
-- 
2.20.1