linux-kernel - [RFC 1/2] x86: mark target address as output in 'insb' asm

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Date:   Mon, 10 Jul 2017 16:44:24 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: [RFC 1/2] x86: mark target address as output in 'insb' asm

The -Wmaybe-uninitialized warning triggers for one driver using the output
of the 'insb' I/O helper on x86:

drivers/net/wireless/wl3501_cs.c: In function ‘wl3501_mgmt_scan_confirm’:
drivers/net/wireless/wl3501_cs.c:665:9: error: ‘sig.status’ is used uninitialized in this function [-Werror=uninitialized]
drivers/net/wireless/wl3501_cs.c:668:12: error: ‘sig.cap_info’ may be used uninitialized in this function [-Werror=maybe-uninitialized]

Apparently the assember constraints are slightly off here, as marking the
'addr' argument as a memory output seems appropriate here and gets rid
of the warning. For consistency I'm also adding it as input for outsb().

Unfortunately, this fix triggers another problem when CONFIG_KASAN is
set, again only in this one driver:

drivers/net/wireless/wl3501_cs.c: In function 'wl3501_rx_interrupt':
drivers/net/wireless/wl3501_cs.c:1103:1: error: the frame size of 2232 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]

I'm not an x86 person and gcc inline assembly mystifies me all the time,
so please review this carefully and suggest a better way if this is not
how it should be done.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/x86/include/asm/io.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 7afb0e2f07f4..d107251eabd9 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -328,13 +328,13 @@ static inline unsigned type in##bwl##_p(int port)			\
 static inline void outs##bwl(int port, const void *addr, unsigned long count) \
 {									\
 	asm volatile("rep; outs" #bwl					\
-		     : "+S"(addr), "+c"(count) : "d"(port));		\
+		     : "+S"(addr), "+c"(count) : "d"(port), "m" (addr));\
 }									\
 									\
 static inline void ins##bwl(int port, void *addr, unsigned long count)	\
 {									\
 	asm volatile("rep; ins" #bwl					\
-		     : "+D"(addr), "+c"(count) : "d"(port));		\
+		     : "+D"(addr), "+c"(count), "=m" (addr) : "d"(port));\
 }
 
 BUILDIO(b, b, char)
-- 
2.9.0