tools/testing/selftests/mm/cow.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
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@linux-foundation.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-mm@kvack.org
Cc: linux-kselftest@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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];
--
2.43.0
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@linux-foundation.org>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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?
--
Cheers,
David / dhildenb
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@linux-foundation.org>
>> Cc: Shuah Khan <shuah@kernel.org>
>> Cc: linux-mm@kvack.org
>> Cc: linux-kselftest@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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.
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 <akpm@linux-foundation.org>
>>> Cc: Shuah Khan <shuah@kernel.org>
>>> Cc: linux-mm@kvack.org
>>> Cc: linux-kselftest@vger.kernel.org
>>> Cc: linux-kernel@vger.kernel.org
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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.
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?
--
Cheers,
David / dhildenb
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 <akpm@linux-foundation.org>
>>>> Cc: Shuah Khan <shuah@kernel.org>
>>>> Cc: linux-mm@kvack.org
>>>> Cc: linux-kselftest@vger.kernel.org
>>>> Cc: linux-kernel@vger.kernel.org
>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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.
>
> 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
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 <akpm@linux-foundation.org>
>>>>> Cc: Shuah Khan <shuah@kernel.org>
>>>>> Cc: linux-mm@kvack.org
>>>>> Cc: linux-kselftest@vger.kernel.org
>>>>> Cc: linux-kernel@vger.kernel.org
>>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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.
>>
>> 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
On 09.04.25 12:31, David Hildenbrand wrote:
> 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 <akpm@linux-foundation.org>
>>>>>> Cc: Shuah Khan <shuah@kernel.org>
>>>>>> Cc: linux-mm@kvack.org
>>>>>> Cc: linux-kselftest@vger.kernel.org
>>>>>> Cc: linux-kernel@vger.kernel.org
>>>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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.
>>>
>>> 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?
>
Reading
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105562#c29
"Note that sanitizers tend to increase the rate of false positive
warnings, most notably those around -Wmaybe-uninitialized. We recommend
against combining -Werror and [the use of] sanitizers."
Is this maybe related to the use of sanitizers?
--
Cheers,
David / dhildenb
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