"Denis V. Lunev" <d...@openvz.org> writes:
> On 10/16/2015 10:17 AM, Markus Armbruster wrote:
>> "Denis V. Lunev" <d...@openvz.org> writes:
>>
>>> The patch is intended to avoid to perform any operation including
>>> calculation of log function arguments when the log is not enabled due to
>>> various reasons.
>>>
>>> Functions qemu_log and qemu_log_mask are replaced with variadic macros.
>>> Unfortunately the code is not C99 compatible and we can not use
>>> portable __VA_ARGS__ way. There are a lot of warnings in the other
>>> places with --std=c99. Thus the only way to achive the result is to use
>>> args.. GCC extension.
>> Really? We use __VA_ARGS__ all over the place, why won't it work here?
>
> I have received warning like this
> "__VA_ARGS__ can only appear in the expansion of a C99 variadic macro"
> with intermediate version of the patch.
>
> At the moment (with the current version) the replacement to __VA_ARGS__
> works. Something strange has been happen. This syntax is definitely
> better for me.
>
> Will change.
>
>>> Format checking performed by compiler will not suffer by this patch. It
>>> will be done inside in fprintf arguments checking.
>>>
>>> Signed-off-by: Denis V. Lunev <d...@openvz.org>
>>> Signed-off-by: Pavel Butsykin <pbutsy...@virtuozzo.com>
>>> CC: Markus Armbruster <arm...@redhat.com>
>>> CC: Luiz Capitulino <lcapitul...@redhat.com>
>>> CC: Eric Blake <ebl...@redhat.com>
>>> CC: Peter Maydell <peter.mayd...@linaro.org>
>>> ---
>>> include/qemu/log.h | 17 ++++++++++++++---
>>> qemu-log.c | 21 ---------------------
>>> 2 files changed, 14 insertions(+), 24 deletions(-)
>>>
>>> diff --git a/include/qemu/log.h b/include/qemu/log.h
>>> index f880e66..57b8c96 100644
>>> --- a/include/qemu/log.h
>>> +++ b/include/qemu/log.h
>>> @@ -53,7 +53,13 @@ static inline bool qemu_loglevel_mask(int mask)
>>> /* main logging function
>>> */
>>> -void GCC_FMT_ATTR(1, 2) qemu_log(const char *fmt, ...);
>>> +#define qemu_log(args...) \
>>> + do { \
>>> + if (!qemu_log_enabled()) { \
>>> + break; \
>>> + } \
>>> + fprintf(qemu_logfile, args); \
>>> + } while (0)
>> Feels stilted. Like Alex's, I'd prefer something like
>>
>> #define qemu_log(fmt, ...) \
>> do { \
>> if (unlikely(qemu_log_enabled())) { \
>> fprintf(qemu_logfile, fmt, ## __VA_ARGS__); \
>> } \
>> } while (0)
>>
>> I'm no fan of hiding qemu_logfile in qemu_log_enabled(), then using it
>> directly to print to it, but that's a different conversation.
> actually I am fine with any approach :) as there is no difference to me.
> In general, this was taken from another project where I have
> had more code below if. This is just an option to reduce indentation
> to a meaningful piece of the code.
>
>> However, we already have
>>
>> static inline void GCC_FMT_ATTR(1, 0)
>> qemu_log_vprintf(const char *fmt, va_list va)
>> {
>> if (qemu_logfile) {
>> vfprintf(qemu_logfile, fmt, va);
>> }
>> }
>>
>> Wouldn't static inline work for qemu_log(), too?
>
> AFAIK no and the problem is that this could be compiler
> specific.
>
> irbis ~ $ cat 1.c
> #include <stdio.h>
>
> int f()
> {
> return 1;
> }
>
> static inline int test(int a, int b)
> {
> if (a == 1) {
> printf("%d\n", b);
> }
> }
>
> int main()
> {
> test(2, f());
> return 0;
> }
> irbis ~ $
>
> 000000000040056b <main>:
> 40056b: 55 push %rbp
> 40056c: 48 89 e5 mov %rsp,%rbp
> 40056f: b8 00 00 00 00 mov $0x0,%eax
> 400574: e8 bd ff ff ff callq 400536 <f>
> 400579: 89 c6 mov %eax,%esi
> 40057b: bf 02 00 00 00 mov $0x2,%edi
> 400580: e8 bc ff ff ff callq 400541 <test>
> 400585: b8 00 00 00 00 mov $0x0,%eax
> 40058a: 5d pop %rbp
> 40058b: c3 retq
> 40058c: 0f 1f 40 00 nopl 0x0(%rax)
>
>
> as you can see here f() is called before calling to test()
>
> Thus I feel that this inline should be replaced too ;)
Well, what did you expect? You asked the compiler to inline test(), and
it inlined test(). You didn't ask it to inline f(), and it didn't
inline f().
[...]
