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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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.

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 feel strongly about this version comparison thing, I'm fine with
just comparing it to the major number, too.

Wei.

> Jan
> 

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