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

[Mukesh Kumar Chaurasiya]

On Fri, Apr 25, 2025 at 02:46:43PM -0300, Arnaldo Carvalho de Melo wrote:
> On Fri, Apr 25, 2025 at 08:19:02PM +0530, Athira Rajeev wrote:
> > > On 14 Apr 2025, at 7:08 AM, Madhavan Srinivasan <maddy at linux.ibm.com> wrote:
> > > On 4/7/25 5:38 PM, Venkat Rao Bagalkote wrote:
> > >> On 07/04/25 12:10 am, Athira Rajeev wrote:
> > >>>> On 6 Apr 2025, at 10:04 PM, Likhitha Korrapati <likhitha at linux.ibm.com> wrote:
> 
> > >>>> perf build break observed when using gcc 13-3 (FC39 ppc64le)
> > >>>> with the following error.
> 
> > >>>> cpumap.c: In function 'perf_cpu_map__merge':
> > >>>> cpumap.c:414:20: error: argument 1 range [18446744069414584320, 18446744073709551614] exceeds maximum object size 9223372036854775807 [-Werror=alloc-size-larger-than=]
> > >>>>   414 |         tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
> > >>>>       |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >>>> In file included from cpumap.c:4:
> > >>>> /usr/include/stdlib.h:672:14: note: in a call to allocation function 'malloc' declared here
> > >>>>   672 | extern void *malloc (size_t __size) __THROW __attribute_malloc__
> > >>>>       |              ^~~~~~
> > >>>> cc1: all warnings being treated as errors
> 
> > >>>> Error happens to be only in gcc13-3 and not in latest gcc 14.
> > >>>> Even though git-bisect pointed bad commit as:
> > >>>> 'commit f5b07010c13c ("libperf: Don't remove -g when EXTRA_CFLAGS are used")',
> > >>>> issue is with tmp_len being "int". It holds number of cpus and making
> > >>>> it "unsigned int" fixes the issues.
> 
> > >>>> After the fix:
> 
> > >>>>   CC      util/pmu-flex.o
> > >>>>   CC      util/expr-flex.o
> > >>>>   LD      util/perf-util-in.o
> > >>>>   LD      perf-util-in.o
> > >>>>   AR      libperf-util.a
> > >>>>   LINK    perf
> > >>>>   GEN     python/perf.cpython-312-powerpc64le-linux-gnu.so
> 
> > >>>> Signed-off-by: Likhitha Korrapati <likhitha at linux.ibm.com>
> > >>> Looks good to me
> 
> > >>> Reviewed-by: Athira Rajeev <atrajeev at linux.ibm.com>
> 
> > >> Tested this patch on perf-tools-next repo, and this patch fixes the issue.
> 
> > >> Tested-by: Venkat Rao Bagalkote <venkat88 at linux.ibm.com>
> 
> > > Arnaldo, Namhyung,
> 
> > > can you consider pulling this fix? since it is breaking the build in gcc13-3 or
> > > if you have any comments do let us know.
> 
> This isn't the only place in that file where this pattern exists:
> 
> ⬢ [acme at toolbx perf-tools-next]$ grep malloc tools/lib/perf/cpumap.c 
> 	cpus = malloc(sizeof(*cpus) + sizeof(struct perf_cpu) * nr_cpus);
> 	tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
> 	tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
> ⬢ [acme at toolbx perf-tools-next]$
> 
> 
> struct perf_cpu_map *perf_cpu_map__alloc(int nr_cpus)
> {
>         RC_STRUCT(perf_cpu_map) *cpus;
>         struct perf_cpu_map *result;
> 
>         if (nr_cpus == 0)
>                 return NULL;
> 
>         cpus = malloc(sizeof(*cpus) + sizeof(struct perf_cpu) * nr_cpus);
> 
> 
> int perf_cpu_map__merge(struct perf_cpu_map **orig, struct perf_cpu_map *other)
> {
>         struct perf_cpu *tmp_cpus;
>         int tmp_len;
>         int i, j, k;
>         struct perf_cpu_map *merged;
> 
>         if (perf_cpu_map__is_subset(*orig, other))
>                 return 0;
>         if (perf_cpu_map__is_subset(other, *orig)) {
>                 perf_cpu_map__put(*orig);
>                 *orig = perf_cpu_map__get(other);
>                 return 0;
>         }
> 
>         tmp_len = __perf_cpu_map__nr(*orig) + __perf_cpu_map__nr(other);
>         tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
> 
> 
> struct perf_cpu_map *perf_cpu_map__intersect(struct perf_cpu_map *orig,
>                                              struct perf_cpu_map *other)
> {
>         struct perf_cpu *tmp_cpus;
>         int tmp_len;
>         int i, j, k;
>         struct perf_cpu_map *merged = NULL;
> 
>         if (perf_cpu_map__is_subset(other, orig))
>                 return perf_cpu_map__get(orig);
>         if (perf_cpu_map__is_subset(orig, other))
>                 return perf_cpu_map__get(other);
> 
>         tmp_len = max(__perf_cpu_map__nr(orig), __perf_cpu_map__nr(other));
>         tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
> 
> I'm trying to figure out why its only in perf_cpu_map__merge() that this
> triggers :-\
> 
> 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.
> 
> But wouldn't turning this into a calloc() be better?
> 
> Like:
> 
> diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
> index 4454a5987570cfbc..99d21618a252ac0e 100644
> --- a/tools/lib/perf/cpumap.c
> +++ 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?
> 
> - Arnaldo
Isn't it better to use perf_cpu_map__nr. That should fix this problem.

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?

Regards,
Mukesh