[PATCH -next] kasan: fix -Wstringop-overflow warning

[Walter Wu]

Compiling with gcc-9.2.1 points out below warnings.

In function 'memmove',
    inlined from 'kmalloc_memmove_invalid_size' at lib/test_kasan.c:301:2:
include/linux/string.h:441:9: warning: '__builtin_memmove' specified
bound 18446744073709551614 exceeds maximum object size
9223372036854775807 [-Wstringop-overflow=]

Why generate this warnings?
Because our test function deliberately pass a negative number in memmove(),
so we need to make it "volatile" so that compiler doesn't see it.

Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
---
 lib/test_kasan.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index f123b4b8aadf..e3087d90e00d 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -289,6 +289,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
 {
 	char *ptr;
 	size_t size = 64;
+	volatile size_t invalid_size = -2;
 
 	pr_info("invalid size in memmove\n");
 	ptr = kmalloc(size, GFP_KERNEL);
@@ -298,7 +299,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
 	}
 
 	memset((char *)ptr, 0, 64);
-	memmove((char *)ptr, (char *)ptr + 4, -2);
+	memmove((char *)ptr, (char *)ptr + 4, invalid_size);
 	kfree(ptr);
 }
 
-- 
2.18.0