Re: [Qemu-devel] [PATCH] trace/simple: Fix warning and wrong trace file name for MinGW

[Stefan Weil <sw@weilnetz.de>]

Am 28.09.2015 um 09:00 schrieb Markus Armbruster:
> Stefan Weil <sw@weilnetz.de> writes:
>
>> On Windows, getpid() always returns an int value, but pid_t (which is
>> expected by the format string) is either a 32 bit or a 64 bit value.
>>
>> Without a type cast (or a modified format string), the compiler prints
>> a warning when building for 64 bit Windows and the resulting trace_file_name
>> will include a wrong pid:
>>
>> trace/simple.c:332:9: warning:
>>  format ‘%lld’ expects argument of type ‘long long int’,
>>  but argument 2 has type ‘int’ [-Wformat=]
>>
>> Signed-off-by: Stefan Weil <sw@weilnetz.de>
>> ---
>>  trace/simple.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/trace/simple.c b/trace/simple.c
>> index 11ad030..56a624c 100644
>> --- a/trace/simple.c
>> +++ b/trace/simple.c
>> @@ -329,7 +329,8 @@ bool st_set_trace_file(const char *file)
>>      g_free(trace_file_name);
>>  
>>      if (!file) {
>> -        trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, getpid());
>> +        /* Type cast needed for Windows where getpid() returns an int. */
>> +        trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, (pid_t)getpid());
>>      } else {
>>          trace_file_name = g_strdup_printf("%s", file);
>>      }
> First we go to the trouble of defining a platform-dependent FMT_pid, and
> then we get to cast anyway.  Meh.
>
> Can you explain why osdep.h's
>
>     #define FMT_pid "%" PRId64
>
> is appropriate for Windows?

Don't blame me for any strangeness which you might find in Windows. :-)

Mingw-w64 sys/types.h defines pid_t to be either an int or an __int64.
FMT_pid must match these definitions.

But getpid returns an int, not a pid_t...