linux-kernel - Re: [PATCH] selftests/mm: Fix compiler -Wmaybe-uninitialized warning

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Message-ID: <0ec536d2-4b82-4e97-9985-15cd431059ba@arm.com>
Date: Wed, 9 Apr 2025 15:39:41 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/mm: Fix compiler -Wmaybe-uninitialized warning



On 4/9/25 15:27, David Hildenbrand wrote:
> On 09.04.25 11:50, Anshuman Khandual wrote:
>> Following build warning comes up for cow test as 'transferred' variable has
>> not been initialized. Fix the warning via zero init for the variable.
>>
>>    CC       cow
>> cow.c: In function ‘do_test_vmsplice_in_parent’:
>> cow.c:365:61: warning: ‘transferred’ may be used uninitialized [-Wmaybe-uninitialized]
>>    365 |                 cur = read(fds[0], new + total, transferred - total);
>>        |                                                 ~~~~~~~~~~~~^~~~~~~
>> cow.c:296:29: note: ‘transferred’ was declared here
>>    296 |         ssize_t cur, total, transferred;
>>        |                             ^~~~~~~~~~~
>>    CC       compaction_test
>>    CC       gup_longterm
>>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Shuah Khan <shuah@...nel.org>
>> Cc: linux-mm@...ck.org
>> Cc: linux-kselftest@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>>   tools/testing/selftests/mm/cow.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
>> index f0cb14ea8608..b6cfe0a4b7df 100644
>> --- a/tools/testing/selftests/mm/cow.c
>> +++ b/tools/testing/selftests/mm/cow.c
>> @@ -293,7 +293,7 @@ static void do_test_vmsplice_in_parent(char *mem, size_t size,
>>           .iov_base = mem,
>>           .iov_len = size,
>>       };
>> -    ssize_t cur, total, transferred;
>> +    ssize_t cur, total, transferred = 0;
>>       struct comm_pipes comm_pipes;
>>       char *old, *new;
>>       int ret, fds[2];
> 
> 
> if (before_fork) {
>     transferred = vmsplice(fds[1], &iov, 1, 0);
> ...
> 
> if (!before_fork) {
>     transferred = vmsplice(fds[1], &iov, 1, 0);
> ...
> 
> for (total = 0; total < transferred; total += cur) {
> ...
> 
> 
> And I don't see any jump label that could jump to code that would ve using transferred.
> 
> What am I missing?

Probably because both those conditional statements are not mutually
exclusive above with an if-else construct. Hence compiler flags it
rather as a false positive ? Initializing with 0 just works around
that false positive.