> On Aug 1, 2019, at 8:07 AM, Qian Cai <[email protected]> wrote:
>
>
>
>> On Aug 1, 2019, at 8:01 AM, Will Deacon <[email protected]> wrote:
>>
>> On Wed, Jul 31, 2019 at 04:38:18PM -0400, Qian Cai wrote:
>>> When CONFIG_KASAN_SW_TAGS=n, set_tag() is compiled away. GCC throws a
>>> warning,
>>>
>>> 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 = 0xff;
>>> ^~~
>>>
>>> Fix it by making __tag_set() a static inline function.
>>>
>>> Signed-off-by: Qian Cai <[email protected]>
>>> ---
>>> arch/arm64/include/asm/memory.h | 6 +++++-
>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> 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;
>>> +}
>>
>> 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) … __tag_set(__addr, page_kasan_tag(page)); …
>
> static inline u8 page_kasan_tag(const struct page *page)
> {
> return 0xff;
> }
>
> GCC will see that “page” is used.
If you are talking about “addr”,
#define __tag_set(addr, tag) (addr)
It is actually used.
