[systemd-devel] [PATCH 2/2] macro: allow assert_se() assertions to also be optimized out when NDEBUG is set

[Shawn Landden]

On Thu, Mar 26, 2015 at 1:19 AM, Lennart Poettering
<lennart at poettering.net> wrote:
> On Tue, 24.03.15 11:11, Shawn Landden (shawn at churchofgit.com) wrote:
>
>> Will result in slightly smaller binaries, and cuts out the branch, even if
>> the expression is still executed.
>
> I am sorry, but the whole point of assert_se() is that it has side
> effects. That's why it is called that way (the "se" suffix stands for
> "side effects"), and is different from assert(). You are supposed to
> use it whenever the code enclosed in it shall not be suppressed if
> NDEBUG is defined. This patch of yours breaks that whole logic!

+#define assert_se(expr) do {expr} while(false)
 #define assert(expr) do {} while(false)

No it does not. see "{expr}", it still is doing the side effect. It
just doesn't check if the return value is as expected.
>
> Lennart
>
>> ---
>>  src/shared/macro.h | 12 ++++++------
>>  1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/src/shared/macro.h b/src/shared/macro.h
>> index 7f89951..02219ea 100644
>> --- a/src/shared/macro.h
>> +++ b/src/shared/macro.h
>> @@ -212,17 +212,17 @@ static inline unsigned long ALIGN_POWER2(unsigned long u) {
>>                  (__x / __y + !!(__x % __y));                            \
>>          })
>>
>> -#define assert_se(expr)                                                 \
>> -        do {                                                            \
>> -                if (_unlikely_(!(expr)))                                \
>> -                        log_assert_failed(#expr, __FILE__, __LINE__, __PRETTY_FUNCTION__); \
>> -        } while (false)                                                 \
>> -
>>  /* We override the glibc assert() here. */
>>  #undef assert
>>  #ifdef NDEBUG
>> +#define assert_se(expr) do {expr} while(false)
>>  #define assert(expr) do {} while(false)
>>  #else
>> +#define assert_se(expr)                                                 \
>> +        do {                                                            \
>> +                if (_unlikely_(!(expr)))                                \
>> +                        log_assert_failed(#expr, __FILE__, __LINE__, __PRETTY_FUNCTION__); \
>> +        } while (false)
>>  #define assert(expr) assert_se(expr)
>>  #endif
>>
>> --
>> 2.2.1.209.g41e5f3a
>>
>> _______________________________________________
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>> systemd-devel at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/systemd-devel
>
>
> Lennart
>
> --
> Lennart Poettering, Red Hat
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-- 
Shawn Landden