Re: [PATCH] tools/lib/perf: Fix -Werror=alloc-size-larger-than in cpumap.c

[Likhitha Korrapati <likhitha@linux.ibm.com>]

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@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