Re: [Qemu-devel] [PATCH] w32: Always use standard instead of native format strings

[Stefan Weil <sw@weilnetz.de>]

Am 24.09.2012 21:28, schrieb Eric Blake:
> On 08/22/2012 01:42 PM, Stefan Weil wrote:
>> GLib 2.0 include files use __printf__ for the format attribute
>> which resolves to native format strings on w32 hosts.
>>
>> QEMU wants standard format strings instead of native format
>> strings, so we simply change any declaration with __printf__
>> to use __gnu_printf__.
>>
>> This works because all basic printf functions support both
>> kinds of format strings.
>>
>> This fixes a compiler warning:
>>
>> qapi/string-output-visitor.c: In function ‘print_type_int’:
>> qapi/string-output-visitor.c:34:5: warning: unknown conversion type character ‘l’ in format [-Wformat]
>> qapi/string-output-visitor.c:34:5: warning: too many arguments for format [-Wformat-extra-args]
>>
>> Signed-off-by: Stefan Weil<sw@weilnetz.de>
>> ---
>>   compiler.h |    5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/compiler.h b/compiler.h
>> index 07ba1f8..c734a71 100644
>> --- a/compiler.h
>> +++ b/compiler.h
>> @@ -44,6 +44,11 @@
>>      /* Use gnu_printf when supported (qemu uses standard format strings). */
>>   #  define GCC_ATTR __attribute__((__unused__, format(gnu_printf, 1, 2)))
>>   #  define GCC_FMT_ATTR(n, m) __attribute__((format(gnu_printf, n, m)))
>> +#  if defined(_WIN32)
>> +    /* Map __printf__ to __gnu_printf__ because we want standard format strings
>> +     * even when MinGW or GLib include files use __printf__. */
>> +#   define __printf__ __gnu_printf__
>> +#  endif
>
> Don't you need to make this conditional on the gcc version?  That is,
> gcc 4.4 added __gnu_printf__, but gcc 4.3 understands only __printf__
> and attempts to pass __gnu_printf__ will cause compilation failure.
>

It is conditional. The complete code is here:

# if !QEMU_GNUC_PREREQ(4, 4)
    /* gcc versions before 4.4.x don't support gnu_printf, so use printf. */
#  define GCC_ATTR __attribute__((__unused__, format(printf, 1, 2)))
#  define GCC_FMT_ATTR(n, m) __attribute__((format(printf, n, m)))
# else
    /* Use gnu_printf when supported (qemu uses standard format strings). */
#  define GCC_ATTR __attribute__((__unused__, format(gnu_printf, 1, 2)))
#  define GCC_FMT_ATTR(n, m) __attribute__((format(gnu_printf, n, m)))
#  if defined(_WIN32)
     /* Map __printf__ to __gnu_printf__ because we want standard format 
strings
      * even when MinGW or GLib include files use __printf__. */
#   define __printf__ __gnu_printf__
#  endif
# endif

gcc 4.3 and older will still produce compiler warnings.