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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Fri, Apr 25, 2025 at 08:19:02PM +0530, Athira Rajeev wrote:
> > On 14 Apr 2025, at 7:08 AM, Madhavan Srinivasan <maddy@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@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@linux.ibm.com>
> >>> Looks good to me

> >>> Reviewed-by: Athira Rajeev <atrajeev@linux.ibm.com>

> >> Tested this patch on perf-tools-next repo, and this patch fixes the issue.

> >> Tested-by: Venkat Rao Bagalkote <venkat88@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@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@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@toolbx perf-tools-next]$


And better, do the max size that the compiler is trying to help us
catch?

- Arnaldo