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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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+.

And then - how is all of this supposed to be working in conjucntion
with live patching, where the patch may have been created by yet
another compiler version?

Jan


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