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

[Likhitha Korrapati]

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