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[2003:cb:c70d:8400:ed9b:a3a:88e5:c6a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39d8938a500sm1223602f8f.49.2025.04.09.03.31.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Apr 2025 03:31:13 -0700 (PDT) Message-ID: Date: Wed, 9 Apr 2025 12:31:12 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] selftests/mm: Fix compiler -Wmaybe-uninitialized warning To: Anshuman Khandual , linux-mm@kvack.org Cc: Andrew Morton , Shuah Khan , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250409095006.1422620-1-anshuman.khandual@arm.com> <9da46633-e9c1-42a7-b52b-16cf89836abc@redhat.com> <0ec536d2-4b82-4e97-9985-15cd431059ba@arm.com> <5c37c129-a8cb-4f17-8af1-059450083c73@arm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <5c37c129-a8cb-4f17-8af1-059450083c73@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 09.04.25 12:25, Anshuman Khandual wrote: > > > On 4/9/25 15:51, David Hildenbrand wrote: >> On 09.04.25 12:09, Anshuman Khandual wrote: >>> >>> >>> 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 >>>>> Cc: Shuah Khan >>>>> Cc: linux-mm@kvack.org >>>>> Cc: linux-kselftest@vger.kernel.org >>>>> Cc: linux-kernel@vger.kernel.org >>>>> Signed-off-by: Anshuman Khandual >>>>> --- >>>>>    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. >> >> This is something the compiler should clearly be able to verify. before_fork is never changed in that function. >> >> We should not work around wrong compilers. >> >> Which compiler are you using such that you run into this issue? > > gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0 > gcc (GCC) 14.2.1 20250110 (Red Hat 14.2.1-7) Seems to be fine, just like all other compilers people used with this over the years. Maybe something about that compiler is shaky that was fixed in the meantime? -- Cheers, David / dhildenb