[PATCH v2] perf/x86/amd/uncore: Avoid a false positive warning about snprintf truncation in amd_uncore_umc_ctx_init

[Jean Delvare]

Fix the following warning:
  CC [M]  arch/x86/events/amd/uncore.o
arch/x86/events/amd/uncore.c: In function ‘amd_uncore_umc_ctx_init’:
arch/x86/events/amd/uncore.c:951:52: warning: ‘%d’ directive output may be truncated writing between 1 and 10 bytes into a region of size 8 [-Wformat-truncation=]
    snprintf(pmu->name, sizeof(pmu->name), "amd_umc_%d", index);
                                                    ^~
arch/x86/events/amd/uncore.c:951:43: note: directive argument in the range [0, 2147483647]
    snprintf(pmu->name, sizeof(pmu->name), "amd_umc_%d", index);
                                           ^~~~~~~~~~~~
arch/x86/events/amd/uncore.c:951:4: note: ‘snprintf’ output between 10 and 19 bytes into a destination of size 16
    snprintf(pmu->name, sizeof(pmu->name), "amd_umc_%d", index);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As far as I can see, there can't be more than UNCORE_GROUP_MAX (256)
groups and each group can't have more than 255 PMU, so the number
printed by this %d can't exceed 65279, that's only 5 digits and would
fit into the buffer. So it's a false positive warning. But we can
make the compiler happy by declaring index as a 16-bit number.

Signed-off-by: Jean Delvare <jdelvare@xxxxxxx>
---
Changes in v2:
 * Use the proper printf conversion specifier, to be on the safe side.

An alternative fix would be to extend UNCORE_NAME_LEN to 20, the
downside being an increased memory consumption. Depends whether we
expect UNCORE_GROUP_MAX to ever be increased, or groups to ever
support more than 255 PMU.

 arch/x86/events/amd/uncore.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- linux-6.12-rc6.orig/arch/x86/events/amd/uncore.c
+++ linux-6.12-rc6/arch/x86/events/amd/uncore.c
@@ -916,7 +916,8 @@ int amd_uncore_umc_ctx_init(struct amd_u
 	u8 group_num_pmcs[UNCORE_GROUP_MAX] = { 0 };
 	union amd_uncore_info info;
 	struct amd_uncore_pmu *pmu;
-	int index = 0, gid, i;
+	int gid, i;
+	u16 index = 0;
 
 	if (pmu_version < 2)
 		return 0;
@@ -948,7 +949,7 @@ int amd_uncore_umc_ctx_init(struct amd_u
 	for_each_set_bit(gid, gmask, UNCORE_GROUP_MAX) {
 		for (i = 0; i < group_num_pmus[gid]; i++) {
 			pmu = &uncore->pmus[index];
-			snprintf(pmu->name, sizeof(pmu->name), "amd_umc_%d", index);
+			snprintf(pmu->name, sizeof(pmu->name), "amd_umc_%hu", index);
 			pmu->num_counters = group_num_pmcs[gid] / group_num_pmus[gid];
 			pmu->msr_base = MSR_F19H_UMC_PERF_CTL + i * pmu->num_counters * 2;
 			pmu->rdpmc_base = -1;


-- 
Jean Delvare
SUSE L3 Support