[PATCH] tools/lib/perf: Fix -Werror=alloc-size-larger-than in cpumap.c
Likhitha Korrapati
likhitha at linux.ibm.com
Wed May 21 23:03:43 AEST 2025
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.
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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