Re: Move tst-signal-numbers to Python

[Florian Weimer <fweimer at redhat dot com>]

* Joseph Myers:

> On Mon, 10 Dec 2018, Florian Weimer wrote:
>
>> I would expect something not based on regular expression for those
>> filters, and it's odd there are two of them.  I don't think using two
>> filters does not include expressiveness here.
>> 
>>     re_signal_macro = re.compile(r'^SIG[A-Z].*')
>>     ignored_macros = set("SIGCLD SIGIOT SIGSWI SIGUNUSED"
>>                          " SIGSTKSZ SIGRTMIN SIGRTMAX".split())
>>     def signal_macro(name):
>>       return re_signal_macro.match(name) and name not in ignored_macros
>
> I don't want to require separate Python code for each such test.

Why not?

> Once there are a few more such tests, I think it will become natural
> to have a single Python script that reads text files describing the
> headers and constants to compare - with separate Python code only for
> more unusual cases.

I still think the comment you included in your patch, listing the signal
names explicitly, is a strong hint that regular expressions are not the
right interface here.

> I think having a regular expression to describe macros to include, and one 
> to describe those to exclude, naturally matches multiple use cases for 
> such tests.  Consider e.g. a test for MAP_* macros, which might compare 
> MAP_[A-Z].* but exclude MAP_HUGE_[0-9].* from the comparison, without 
> wanting to list all the macros such as MAP_HUGE_256MB individually.  
> (That's an example of a case that will also need a kernel version to be 
> specified, so that extra macros are allowed on the glibc side if the 
> kernel headers are older, and extra macros are allowed on the kernel side 
> if the kernel headers are newer.)

The other issue to consider is that the current approach only works if
GCC can interpret the macro constant as a long int.  (I think the cast
in an input constraint is not really a C cast.)  Future macro
comparisons may well need type annotations, and that that point, regular
expressions seem rather problematic to me.

But please do not let this block you.  It's just a test.  I don't have a
strong opinion about all this.

Thanks,
Florian