Re: [PATCH] Check jvmti_agent snprintf return value to avoid build failures with GCC-8.1.1

[William Cohen <wcohen@redhat.com>]

On 07/10/2018 06:58 PM, Jiri Olsa wrote:
> On Tue, Jul 10, 2018 at 02:27:16PM -0400, William Cohen wrote:
>> Newer versions of GCC perform static analysis to determine whether
>> string truncation is possible with functions such as snprintf and
>> provide a warning if truncation could occur.  The make for
>> jvmti_agent.c uses the compiler option that treats any compiler
>> warnings as compiler errors.  For GCC-8.1.1 in Fedora 28 this causes
>> the build to fail.  The return value of the snprint is now checked to
>> ensure snprintf produced a NULL-terminated string.  If the string for
>> the path is invalid, the code does attempt to use the string.
> 
> hi,
> I posted fix for this recently:
>   https://lore.kernel.org/lkml/20180702134202.17745-1-jolsa@kernel.org/
> 
> it also covers the perf_regs.c, which was failing with gcc8 for me
> 
> should be pulled in soon
> 
> thanks,
> jirka

Hi Jirka,

Thanks.  I hadn't seen the patch, and this failing to build for the past week has been bugging me.  Glad to hear there is already a fix queued up.

-Will
> 
>>
>> Signed-off-by: William Cohen <wcohen@redhat.com>
>> ---
>>  tools/perf/jvmti/jvmti_agent.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/jvmti/jvmti_agent.c b/tools/perf/jvmti/jvmti_agent.c
>> index 0c6d1002b524..30f14eafe4b3 100644
>> --- a/tools/perf/jvmti/jvmti_agent.c
>> +++ b/tools/perf/jvmti/jvmti_agent.c
>> @@ -227,7 +227,7 @@ void *jvmti_open(void)
>>  {
>>  	char dump_path[PATH_MAX];
>>  	struct jitheader header;
>> -	int fd;
>> +	int retlen, fd;
>>  	FILE *fp;
>>  
>>  	init_arch_timestamp();
>> @@ -249,7 +249,10 @@ void *jvmti_open(void)
>>  	/*
>>  	 * jitdump file name
>>  	 */
>> -	snprintf(dump_path, PATH_MAX, "%s/jit-%i.dump", jit_path, getpid());
>> +	retlen = snprintf(dump_path, PATH_MAX, "%s/jit-%i.dump",
>> +			  jit_path, getpid());
>> +	if (retlen <= 0 || ((int) sizeof(dump_path)) <= retlen)
>> +		return NULL;
>>  
>>  	fd = open(dump_path, O_CREAT|O_TRUNC|O_RDWR, 0666);
>>  	if (fd == -1)
>> -- 
>> 2.17.1
>>