[OpenWrt-Devel] [PATCH] procd: Fix compile error with GCC8

[Arjen de Korte]

Citeren John Crispin <john at phrozen.org>:

> On 21/06/18 22:58, Rosen Penev wrote:
>> error: ‘%d’ directive output may be truncated writing between 2 and 10
>> bytes into a region of size 3 [-Werror=format-truncation=]
>> snprintf(fd_buf, sizeof(fd_buf), "%d", wdt_fd);
>>                                     ^~~
>> note: directive argument in the range [0, 2147483647]
>> snprintf(fd_buf, sizeof(fd_buf), "%d", wdt_fd);
>>                                    ^~~~~
>> note: ‘snprintf’ output between 3 and 11 bytes into a destination of size
>> 3
>> snprintf(fd_buf, sizeof(fd_buf), "%d", wdt_fd);
>>
>> Signed-off-by: Rosen Penev <rosenp at gmail.com>
>> ---
>>  watchdog.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/watchdog.c b/watchdog.c
>> index ec10ba6..efe30f1 100644
>> --- a/watchdog.c
>> +++ b/watchdog.c
>> @@ -144,8 +144,9 @@ char* watchdog_fd(void)
>>  {
>>  	static char fd_buf[3];
>>  -	if (wdt_fd < 0)
>> +	if (wdt_fd < 0 || wdt_fd > 99)
>>  		return NULL;
>> +
>>  	snprintf(fd_buf, sizeof(fd_buf), "%d", wdt_fd);
> imho the %d should be changed to %ld or something similar.

That's not the problem here. The fd_buf is only large enough to store  
values between 0 and 99 (inclusive). Although this will fix the  
compilation warning/error, I'm slightly worried that this may confuse  
callers when the filedescriptor is > 99. Before this patch, you'd get  
a truncated value (the first two digits), after there will be no  
difference between an error condition (wdt_fd < 0) or a filedescriptor  
that is too large to fit in the static fd_buf.

The wdt_fd is defined as an 'int', so %d is appropriate here.

>>    	return fd_buf;
>
>
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