Re: [Xen-devel] [PATCH 2 of 3] xen/debug: Introduce ASSERT_PRINTK()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.10.12 at 11:29, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:

> On 15/10/12 10:17, Jan Beulich wrote:
>>>>> On 08.10.12 at 20:16, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>>> This is a variant of ASSERT() which takes a predicate, and a variable
>>> number of arguments which get fed to prink() before the BUG().
>>>
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>
>>> --
>>> This does use C99 varadic macros, but given that we use other C99
>>> features without #ifdef guards, I felt it not necessary to guard this as
>>> well.
>>>
>>> diff -r 2927e18e9a7c -r 477ccdb9870e xen/include/xen/lib.h
>>> --- a/xen/include/xen/lib.h
>>> +++ b/xen/include/xen/lib.h
>>> @@ -38,11 +38,26 @@ do {                                    
>>>  } while (0)
>>>  #endif
>>>  
>>> +#ifndef assert_printk_failed
>>> +#define assert_printk_failed(p, ...)                            \
>>> +do {                                                            \
>>> +    printk("Assertion '%s' failed, line %d, file %s\n", p ,     \
>>> +                   __LINE__, __FILE__);                         \
>>> +    printk(__VA_ARGS__);                                        \
>> The first argument here necessarily is a format string, so it
>> should also be enforced that way.
> 
> Except for the trailing comma issue present in C99 varadic macros, which
> is why it is specified this way.
> 
> #define COMMA(fmt, ...) printf(fmt, _VA_ARGS__);
> 
> Calling COMMA("foobar") will expand to 'printf("foobar",);' leading to a
> syntax error.  There is a GCCism which fixes this issue, but it is not
> portable.

But this is not a public header, so gcc-isms are no problem.

Jan


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