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

[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@suse.de>
---
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

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

[Sandipan Das]

On 11/5/2024 2:22 PM, Jean Delvare wrote:
> 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@suse.de>
> ---
> 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.
> 

Its very unlikely for UNCORE_GROUP_MAX to change and the current
solution looks good to me.

Reviewed-by: Sandipan Das <sandipan.das@amd.com>

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

[tip-bot2 for Jean Delvare]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     2e71e8bc6f02275a67bcb882779ab6d21abc68c4
Gitweb:        https://git.kernel.org/tip/2e71e8bc6f02275a67bcb882779ab6d21abc68c4
Author:        Jean Delvare <jdelvare@suse.de>
AuthorDate:    Tue, 05 Nov 2024 09:52:53 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 11 Nov 2024 11:49:47 +01:00

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

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@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sandipan Das <sandipan.das@amd.com>
Link: https://lore.kernel.org/r/20241105095253.18f34b4d@endymion.delvare
---
 arch/x86/events/amd/uncore.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
index 0bfde2e..49c26ce 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -916,7 +916,8 @@ int amd_uncore_umc_ctx_init(struct amd_uncore *uncore, unsigned int cpu)
 	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_uncore *uncore, unsigned int cpu)
 	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;