[PATCH] [v3] kasan: avoid -Wmaybe-uninitialized warning

[PATCH] [v3] kasan: avoid -Wmaybe-uninitialized warning

[Arnd Bergmann]

gcc-7 produces this warning:

mm/kasan/report.c: In function 'kasan_report':
mm/kasan/report.c:351:3: error: 'info.first_bad_addr' may be used uninitialized in this function [-Werror=maybe-uninitialized]
   print_shadow_for_address(info->first_bad_addr);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/kasan/report.c:360:27: note: 'info.first_bad_addr' was declared here

The code seems fine as we only print info.first_bad_addr when there is a shadow,
and we always initialize it in that case, but this is relatively hard
for gcc to figure out after the latest rework. Adding an intialization
to the most likely value together with the other struct members
shuts up that warning.

Fixes: b235b9808664 ("kasan: unify report headers")
Link: https://patchwork.kernel.org/patch/9641417/
Suggested-by: Alexander Potapenko <glider@google.com>
Suggested-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
Originally submitted on March 23, but unfortunately is still needed,
as verified on 4.13-rc1, with aarch64-linux-gcc-7.1.1

v2: add a comment as Andrew suggested
v3: move initialization as Alexander and Andrey suggested
---
 mm/kasan/report.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 04bb1d3eb9ec..6bcfb01ba038 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -401,6 +401,7 @@ void kasan_report(unsigned long addr, size_t size,
 	disable_trace_on_warning();
 
 	info.access_addr = (void *)addr;
+	info.first_bad_addr = (void *)addr;
 	info.access_size = size;
 	info.is_write = is_write;
 	info.ip = ip;
-- 
2.9.0

Re: [PATCH] [v3] kasan: avoid -Wmaybe-uninitialized warning

[Andrey Ryabinin]

On 07/25/2017 06:27 PM, Arnd Bergmann wrote:
> gcc-7 produces this warning:
> 
> mm/kasan/report.c: In function 'kasan_report':
> mm/kasan/report.c:351:3: error: 'info.first_bad_addr' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    print_shadow_for_address(info->first_bad_addr);
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/kasan/report.c:360:27: note: 'info.first_bad_addr' was declared here
> 
> The code seems fine as we only print info.first_bad_addr when there is a shadow,
> and we always initialize it in that case, but this is relatively hard
> for gcc to figure out after the latest rework. Adding an intialization
> to the most likely value together with the other struct members
> shuts up that warning.
> 
> Fixes: b235b9808664 ("kasan: unify report headers")
> Link: https://patchwork.kernel.org/patch/9641417/
> Suggested-by: Alexander Potapenko <glider@google.com>
> Suggested-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>