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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.10.16 at 17:33, <wei.liu2@xxxxxxxxxx> wrote:
> On Wed, Oct 12, 2016 at 06:42:53AM -0600, Jan Beulich wrote:
>> >>> On 11.10.16 at 12:31, <wei.liu2@xxxxxxxxxx> wrote:
>> > --- /dev/null
>> > +++ b/xen/common/gcov/gcc_4_7.c
>> > @@ -0,0 +1,205 @@
>> > +/*
>> > + *  This code provides functions to handle gcc's profiling data format
>> > + *  introduced with gcc 4.7.
>> > + *
>> > + *  This file is based heavily on gcc_3_4.c file.
>> > + *
>> > + *  For a better understanding, refer to gcc source:
>> > + *  gcc/gcov-io.h
>> > + *  libgcc/libgcov.c
>> > + *
>> > + *  Uses gcc-internal data definitions.
>> > + *
>> > + *  Imported from Linux and modified for Xen by
>> > + *    Wei Liu <wei.liu2@xxxxxxxxxx>
>> > + */
>> > +
>> > +#include <xen/string.h>
>> > +
>> > +#include "gcov.h"
>> > +
>> > +#if GCC_VERSION < 40700
>> > +#error "Wrong version of GCC used to compile gcov"
>> > +#endif
>> > +
>> > +#if (__GNUC__ > 5) || (__GNUC__ == 5 && __GNUC_MINOR__ >= 1)
>> > +#define GCOV_COUNTERS                   10
>> > +#elif __GNUC__ == 4 && __GNUC_MINOR__ >= 9
>> > +#define GCOV_COUNTERS                   9
>> > +#else
>> > +#define GCOV_COUNTERS                   8
>> > +#endif
>> 
>> I'm sorry for not having pointed this out on v2 (I had noticed it,
>> but then didn't finish analyzing the situation), but I'm afraid this
>> together with ...
>> 
>> > +struct gcov_info {
>> > +    unsigned int version;
>> > +    struct gcov_info *next;
>> > +    unsigned int stamp;
>> > +    const char *filename;
>> > +    void (*merge[GCOV_COUNTERS])(gcov_type *, unsigned int);
>> > +    unsigned int n_functions;
>> > +    struct gcov_fn_info **functions;
>> > +};
>> 
>> ... 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've broken down things into several files as well as provided
> corresponding Kconfig options:
> 
>  gcc_4_7_base.c: the body of what is now gcc_4_7.c, better name is
>                  welcome

Why don't you keep it gcc_4_7.c, with its counter definition being
conditional upon the symbol not already being defined?

Jan


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