| Message ID | 20210211125602.44248-1-vincenzo.frascino@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: Fix warning in mte_get_random_tag() | expand |
On Thu, 11 Feb 2021 at 13:57, Vincenzo Frascino <vincenzo.frascino@arm.com> wrote: > > The simplification of mte_get_random_tag() caused the introduction of the > warning below: > > In file included from arch/arm64/include/asm/kasan.h:9, > from include/linux/kasan.h:16, > from mm/kasan/common.c:14: > mm/kasan/common.c: In function ‘mte_get_random_tag’: > arch/arm64/include/asm/mte-kasan.h:45:9: warning: ‘addr’ is used > uninitialized [-Wuninitialized] > 45 | asm(__MTE_PREAMBLE "irg %0, %0" > | > > Fix the warning initializing the address to NULL. > > Note: mte_get_random_tag() returns a tag and it never dereferences the address, > hence 'addr' can be safely initialized to NULL. > > Fixes: c8f8de4c0887 ("arm64: kasan: simplify and inline MTE functions") > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: Andrey Konovalov <andreyknvl@google.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> > --- > > This patch is based on linux-next/akpm > > arch/arm64/include/asm/mte-kasan.h | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h > index 3d58489228c0..b2850b750726 100644 > --- a/arch/arm64/include/asm/mte-kasan.h > +++ b/arch/arm64/include/asm/mte-kasan.h > @@ -40,7 +40,12 @@ static inline u8 mte_get_mem_tag(void *addr) > /* Generate a random tag. */ > static inline u8 mte_get_random_tag(void) > { > - void *addr; > + /* > + * mte_get_random_tag() returns a tag and it > + * never dereferences the address, hence addr > + * can be safely initialized to NULL. > + */ > + void *addr = NULL; > > asm(__MTE_PREAMBLE "irg %0, %0" > : "+r" (addr)); > -- > 2.30.0 > Might it be better to simply change the asm constraint to "=r" ?
On 2/11/21 1:35 PM, Ard Biesheuvel wrote: > On Thu, 11 Feb 2021 at 13:57, Vincenzo Frascino > <vincenzo.frascino@arm.com> wrote: >> >> The simplification of mte_get_random_tag() caused the introduction of the >> warning below: >> >> In file included from arch/arm64/include/asm/kasan.h:9, >> from include/linux/kasan.h:16, >> from mm/kasan/common.c:14: >> mm/kasan/common.c: In function ‘mte_get_random_tag’: >> arch/arm64/include/asm/mte-kasan.h:45:9: warning: ‘addr’ is used >> uninitialized [-Wuninitialized] >> 45 | asm(__MTE_PREAMBLE "irg %0, %0" >> | >> >> Fix the warning initializing the address to NULL. >> >> Note: mte_get_random_tag() returns a tag and it never dereferences the address, >> hence 'addr' can be safely initialized to NULL. >> >> Fixes: c8f8de4c0887 ("arm64: kasan: simplify and inline MTE functions") >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Cc: Andrey Konovalov <andreyknvl@google.com> >> Cc: Andrew Morton <akpm@linux-foundation.org> >> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> >> --- >> >> This patch is based on linux-next/akpm >> >> arch/arm64/include/asm/mte-kasan.h | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h >> index 3d58489228c0..b2850b750726 100644 >> --- a/arch/arm64/include/asm/mte-kasan.h >> +++ b/arch/arm64/include/asm/mte-kasan.h >> @@ -40,7 +40,12 @@ static inline u8 mte_get_mem_tag(void *addr) >> /* Generate a random tag. */ >> static inline u8 mte_get_random_tag(void) >> { >> - void *addr; >> + /* >> + * mte_get_random_tag() returns a tag and it >> + * never dereferences the address, hence addr >> + * can be safely initialized to NULL. >> + */ >> + void *addr = NULL; >> >> asm(__MTE_PREAMBLE "irg %0, %0" >> : "+r" (addr)); >> -- >> 2.30.0 >> > > Might it be better to simply change the asm constraint to "=r" ? > Indeed, did not notice the "+r". I will change it accordingly and post v2. Thanks!
diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h index 3d58489228c0..b2850b750726 100644 --- a/arch/arm64/include/asm/mte-kasan.h +++ b/arch/arm64/include/asm/mte-kasan.h @@ -40,7 +40,12 @@ static inline u8 mte_get_mem_tag(void *addr) /* Generate a random tag. */ static inline u8 mte_get_random_tag(void) { - void *addr; + /* + * mte_get_random_tag() returns a tag and it + * never dereferences the address, hence addr + * can be safely initialized to NULL. + */ + void *addr = NULL; asm(__MTE_PREAMBLE "irg %0, %0" : "+r" (addr));
The simplification of mte_get_random_tag() caused the introduction of the warning below: In file included from arch/arm64/include/asm/kasan.h:9, from include/linux/kasan.h:16, from mm/kasan/common.c:14: mm/kasan/common.c: In function ‘mte_get_random_tag’: arch/arm64/include/asm/mte-kasan.h:45:9: warning: ‘addr’ is used uninitialized [-Wuninitialized] 45 | asm(__MTE_PREAMBLE "irg %0, %0" | Fix the warning initializing the address to NULL. Note: mte_get_random_tag() returns a tag and it never dereferences the address, hence 'addr' can be safely initialized to NULL. Fixes: c8f8de4c0887 ("arm64: kasan: simplify and inline MTE functions") Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Andrey Konovalov <andreyknvl@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> --- This patch is based on linux-next/akpm arch/arm64/include/asm/mte-kasan.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)