Re: [Xen-devel] [PATCH v3] gcov: add new interface and 3.4 and 4.7 format support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.10.16 at 10:49, <wei.liu2@xxxxxxxxxx> wrote:
> On Thu, Oct 13, 2016 at 02:29:08AM -0600, Jan Beulich wrote:
> [...]
>> >> >> ... this structure's trailing fields actually getting used by the code
>> >> >> won't work well when changing compiler versions without cleaning
>> >> >> the tree. I think instead you need thin gcc_5.c and gcc_4_9.c
>> >> >> #define-ing their GCOV_COUNTERS and then #include-ing this
>> >> >> shared source file. Plus btw, I don't think gcc 5.0.x (the
>> >> >> development variant of 5.x) would use anything different from
>> >> >> 5.1.x or 5.2.x; in fact use of __GNUC_MINOR__ should not
>> >> >> normally be necessary anymore with gcc 5+.
>> >> >> 
>> >> > 
>> >> > I think you misread here: __GNUC_MINOR__ is the "x" part of 5.x.y, the
>> >> > "y" part is __GNUC_PATCHLEVEL__.
>> >> 
>> >> No, I didn't. From 5.x onwards the information previously carried in
>> >> __GNUC_PATCHLEVEL__ is now in __GNUC_MINOR__. And as much
>> >> as previously you would not normally need to look at the former,
>> >> with newer gcc you shouldn't need to look at the latter.
>> >> 
>> > 
>> > I can't find relevant information in GCC cpp manual.
>> > 
>> > Specifically, I look at 4.9.4 and 5.4.0 doc:
>> > 
>> > 
> https://gcc.gnu.org/onlinedocs/gcc-4.9.4/cpp/Common-Predefined-Macros.html#Comm
>  
> 
>> > on-Predefined-Macros
>> > 
> https://gcc.gnu.org/onlinedocs/gcc-5.4.0/cpp/Common-Predefined-Macros.html#Comm
>  
> 
>> > on-Predefined-Macros
>> > 
>> > The sections about __GNUC_* macros are identical, their semantics stay
>> > the same.
>> > 
>> > What did I miss?
>> 
>> Their change in how version numbers get used. I'm sure you've noticed
>> there never was a released 5.0.0 or 6.0.0, and that the stable updates
>> following 5.1.0 were 5.2.0, 5.3.0, etc.
>> 
> 
> OK. I found the bits at https://gcc.gnu.org/develop.html. I see what you
> meant previously.
> 
> It doesn't seem to be a problem to me to compare to 5.1 though -- that's
> the first release of gcc 5, which should be what people use anyway.

But your check should cover the introduction point of the feature,
which is 5.0.0 imo.

> If it is the complexity of the macro that concerns you, now it has been
> changed to use GCC_VERSION macro in gcov.h, which is a lot simpler to
> reason about. Are you happy with such arrangement?

If you mean this to be an adjustment newer than v3, then I think
I'd be fine with that, provided you cover the full range (as indicated
above), i.e. starting at 5.0.0.

Jan


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