GCC (15.2.1) warns on about the following string truncation in blkparse.c

gcc -o blkparse.o -c -Wall -O2 -g -W -D_GNU_SOURCE -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 blkparse.c
blkparse.c: In function ‘main’:
blkparse.c:2103:68: warning: ‘):’ directive output may be truncated writing 2 bytes into a region of size between 1 and 41 [-Wformat-truncation=]
 2103 |                         snprintf(line, sizeof(line) - 1, "CPU%d (%s):",
      |                                                                    ^~
In function ‘show_device_and_cpu_stats’,
    inlined from ‘show_stats’ at blkparse.c:3064:3,
    inlined from ‘main’ at blkparse.c:3386:3:
blkparse.c:2103:25: note: ‘snprintf’ output between 9 and 49 bytes into a destination of size 47
 2103 |                         snprintf(line, sizeof(line) - 1, "CPU%d (%s):",
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 2104 |                                  j, get_dev_name(pdi, name, sizeof(name)));
      |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
gcc -Wall -O2 -g -W -D_GNU_SOURCE -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64  -o blkparse blkparse.o blkparse_fmt.o rbtree.o act_mask.o

Add two more bytes to the string in order to mitigate the compiler warning.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 blkparse.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/blkparse.c b/blkparse.c
index d6aaa8b..3f4d827 100644
--- a/blkparse.c
+++ b/blkparse.c
@@ -2023,7 +2023,7 @@ static void show_device_and_cpu_stats(void)
 	struct io_stats total, *ios;
 	unsigned long long rrate, wrate, msec;
 	int i, j, pci_events;
-	char line[3 + 8/*cpu*/ + 2 + 32/*dev*/ + 3];
+	char line[3 + 8/*cpu*/ + 2 + 32/*dev*/ + 3 + 2];
 	char name[32];
 	double ratio;
 
-- 
2.51.0

On 9/26/25 00:04, Johannes Thumshirn wrote:
> GCC (15.2.1) warns on about the following string truncation in blkparse.c
> 
> gcc -o blkparse.o -c -Wall -O2 -g -W -D_GNU_SOURCE -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 blkparse.c
> blkparse.c: In function ‘main’:
> blkparse.c:2103:68: warning: ‘):’ directive output may be truncated writing 2 bytes into a region of size between 1 and 41 [-Wformat-truncation=]
>  2103 |                         snprintf(line, sizeof(line) - 1, "CPU%d (%s):",
>       |                                                                    ^~
> In function ‘show_device_and_cpu_stats’,
>     inlined from ‘show_stats’ at blkparse.c:3064:3,
>     inlined from ‘main’ at blkparse.c:3386:3:
> blkparse.c:2103:25: note: ‘snprintf’ output between 9 and 49 bytes into a destination of size 47
>  2103 |                         snprintf(line, sizeof(line) - 1, "CPU%d (%s):",
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  2104 |                                  j, get_dev_name(pdi, name, sizeof(name)));
>       |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> gcc -Wall -O2 -g -W -D_GNU_SOURCE -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64  -o blkparse blkparse.o blkparse_fmt.o rbtree.o act_mask.o
> 
> Add two more bytes to the string in order to mitigate the compiler warning.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>


-- 
Damien Le Moal
Western Digital Research