On Thu, 23 Mar 2017 16:04:09 +0100 Arnd Bergmann <arnd@xxxxxxxx> 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
> in the other code path gets rid of the warning.
>
> ...
>
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -109,6 +109,8 @@ const char *get_wild_bug_type(struct kasan_access_info *info)
> {
> const char *bug_type = "unknown-crash";
>
> + info->first_bad_addr = (void *)(-1ul);
> +
> if ((unsigned long)info->access_addr < PAGE_SIZE)
> bug_type = "null-ptr-deref";
> else if ((unsigned long)info->access_addr < TASK_SIZE)
A weird, ugly and seemingly-unneeded statement should have a comment
explaining its existence, no?
Fortunately it is no longer needed. We now have:
static void print_error_description(struct kasan_access_info *info)
{
const char *bug_type = "unknown-crash";
u8 *shadow_addr;
info->first_bad_addr = find_first_bad_addr(info->access_addr,
info->access_size);
shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr);
...
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