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 03:15:09AM -0600, Jan Beulich wrote:
> >>> 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.
> 

OK. The check is now like:

#if GCC_VERSION < 50000
#error "Wrong version of GCC used to compile gcov"
#endif

GCC_VERSION is a convenient marco that you can find in this patch.

Then all reference to gcc 5.1 will be changed to gcc 5.

Wei.

> Jan
> 

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