[PATCH] tools/lib/perf: Fix -Werror=alloc-size-larger-than in cpumap.c
Likhitha Korrapati
likhitha at linux.ibm.com
Thu May 22 03:28:16 AEST 2025
Hi Ian,
On 5/21/25 21:15, Ian Rogers wrote:
> On Wed, May 21, 2025 at 6:03 AM Likhitha Korrapati
> <likhitha at linux.ibm.com> wrote:
>>
>> Hi Arnaldo,
>>
>> On 5/14/25 02:43, Arnaldo Carvalho de Melo wrote:
>>> On Fri, May 02, 2025 at 01:14:32PM +0530, Mukesh Kumar Chaurasiya wrote:
>>>> On Fri, Apr 25, 2025 at 02:46:43PM -0300, Arnaldo Carvalho de Melo wrote:
>>>>> Maybe that max() call in perf_cpu_map__intersect() somehow makes the
>>>>> compiler happy.
>>>
>>>>> And in perf_cpu_map__alloc() all calls seems to validate it.
>>>
>>>>> Like:
>>>
>>>>> +++ b/tools/lib/perf/cpumap.c
>>>>> @@ -411,7 +411,7 @@ int perf_cpu_map__merge(struct perf_cpu_map **orig, struct perf_cpu_map *other)
>>>>> }
>>>>>
>>>>> tmp_len = __perf_cpu_map__nr(*orig) + __perf_cpu_map__nr(other);
>>>>> - tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
>>>>> + tmp_cpus = calloc(tmp_len, sizeof(struct perf_cpu));
>>>>> if (!tmp_cpus)
>>>>> return -ENOMEM;
>>>
>>>>> ⬢ [acme at toolbx perf-tools-next]$
>>>
>>>>> And better, do the max size that the compiler is trying to help us
>>>>> catch?
>>>
>>>> Isn't it better to use perf_cpu_map__nr. That should fix this problem.
>>>
>>> Maybe, have you tried it?
>>
>> I have tried this method and it works.
>>
>> --- a/tools/lib/perf/cpumap.c
>> +++ b/tools/lib/perf/cpumap.c
>> @@ -410,7 +410,7 @@ int perf_cpu_map__merge(struct perf_cpu_map **orig,
>> struct perf_cpu_map *other)
>> return 0;
>> }
>>
>> - tmp_len = max(__perf_cpu_map__nr(*orig), __perf_cpu_map__nr(other));
>> + tmp_len = perf_cpu_map__nr(*orig) + perf_cpu_map__nr(other);
>> tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
>> if (!tmp_cpus)
>> return -ENOMEM;
>>
>> I will send a V2 with this change if this looks good.
>
> How is this different from the existing code:
> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/lib/perf/cpumap.c?h=perf-tools-next#n423
> ```
> tmp_len = __perf_cpu_map__nr(*orig) + __perf_cpu_map__nr(other);
> tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
> if (!tmp_cpus)
> return -ENOMEM;
> ```
>
> Thanks,
> Ian
I gave the wrong diff. Here is the corrected diff.
--- a/tools/lib/perf/cpumap.c
+++ b/tools/lib/perf/cpumap.c
@@ -410,7 +410,7 @@ int perf_cpu_map__merge(struct perf_cpu_map **orig,
struct perf_cpu_map *other)
return 0;
}
- tmp_len = __perf_cpu_map__nr(*orig) + __perf_cpu_map__nr(other);
+ tmp_len = perf_cpu_map__nr(*orig) + perf_cpu_map__nr(other);
tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
if (!tmp_cpus)
return -ENOMEM;
I am using perf_cpu_map__nr instead of __perf_cpu_map__nr.
Thanks,
Likhitha.
>
>> Thanks
>> Likhitha.
>>
>>>
>>>> One question I have, in perf_cpu_map__nr, the function is returning
>>>> 1 in case *cpus is NULL. Is it ok to do that? wouldn't it cause problems?
>>>
>>> Indeed this better be documented, as by just looking at:
>>>
>>> int perf_cpu_map__nr(const struct perf_cpu_map *cpus)
>>> {
>>> return cpus ? __perf_cpu_map__nr(cpus) : 1;
>>> }
>>>
>>> It really doesn't make much sense to say that a NULL map has one entry.
>>>
>>> But the next functions are:
>>>
>>> bool perf_cpu_map__has_any_cpu_or_is_empty(const struct perf_cpu_map *map)
>>> {
>>> return map ? __perf_cpu_map__cpu(map, 0).cpu == -1 : true;
>>> }
>>>
>>> bool perf_cpu_map__is_any_cpu_or_is_empty(const struct perf_cpu_map *map)
>>> {
>>> if (!map)
>>> return true;
>>>
>>> return __perf_cpu_map__nr(map) == 1 && __perf_cpu_map__cpu(map, 0).cpu == -1;
>>> }
>>>
>>> bool perf_cpu_map__is_empty(const struct perf_cpu_map *map)
>>> {
>>> return map == NULL;
>>> }
>>>
>>> So it seems that a NULL cpu map means "any/all CPU) and a map with just
>>> one entry would have as its content "-1" that would mean "any/all CPU".
>>>
>>> Ian did work on trying to simplify/clarify this, so maybe he can chime
>>> in :-)
>>>
>>> - Arnaldo
>>
>
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