> 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.
