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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id h1sm33942126qkh.101.2019.08.01.05.07.12 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Aug 2019 05:07:13 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.11\)) Subject: Re: [PATCH] arm64/mm: fix variable 'tag' set but not used From: Qian Cai In-Reply-To: <20190801120121.6cmtho3wd32nzfoz@willie-the-truck> Date: Thu, 1 Aug 2019 08:07:12 -0400 Cc: Catalin Marinas , andreyknvl@google.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <5E9F5456-3B82-4CB8-868B-1C7B4CBE4CBC@lca.pw> References: <1564605498-17629-1-git-send-email-cai@lca.pw> <20190801120121.6cmtho3wd32nzfoz@willie-the-truck> To: Will Deacon X-Mailer: Apple Mail (2.3445.104.11) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Aug 1, 2019, at 8:01 AM, Will Deacon wrote: >=20 > On Wed, Jul 31, 2019 at 04:38:18PM -0400, Qian Cai wrote: >> When CONFIG_KASAN_SW_TAGS=3Dn, set_tag() is compiled away. GCC throws = a >> warning, >>=20 >> mm/kasan/common.c: In function '__kasan_kmalloc': >> mm/kasan/common.c:464:5: warning: variable 'tag' set but not used >> [-Wunused-but-set-variable] >> u8 tag =3D 0xff; >> ^~~ >>=20 >> Fix it by making __tag_set() a static inline function. >>=20 >> Signed-off-by: Qian Cai >> --- >> arch/arm64/include/asm/memory.h | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >>=20 >> diff --git a/arch/arm64/include/asm/memory.h = b/arch/arm64/include/asm/memory.h >> index b7ba75809751..9645b1340afe 100644 >> --- a/arch/arm64/include/asm/memory.h >> +++ b/arch/arm64/include/asm/memory.h >> @@ -210,7 +210,11 @@ static inline unsigned long kaslr_offset(void) >> #define __tag_reset(addr) untagged_addr(addr) >> #define __tag_get(addr) (__u8)((u64)(addr) >> 56) >> #else >> -#define __tag_set(addr, tag) (addr) >> +static inline const void *__tag_set(const void *addr, u8 tag) >> +{ >> + return addr; >> +} >=20 > Why doesn't this trigger a warning in page_to_virt(), which passes an > unsigned long for the address parameter? #define page_to_virt(page) =E2=80=A6 __tag_set(__addr, = page_kasan_tag(page)); =E2=80=A6 static inline u8 page_kasan_tag(const struct page *page) {=09 return 0xff; } GCC will see that =E2=80=9Cpage=E2=80=9D is used.=