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From: David Marchand <david.marchand@redhat.com>
Date: Wed, 2 Apr 2025 14:16:04 +0200
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Subject: Re: [PATCH v6 8/8] eal: rework function versioning macros
To: Thomas Monjalon <thomas@monjalon.net>
Cc: dev@dpdk.org, bruce.richardson@intel.com, andremue@linux.microsoft.com, 
 Tyler Retzlaff <roretzla@linux.microsoft.com>,
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On Wed, Apr 2, 2025 at 1:53=E2=80=AFPM Thomas Monjalon <thomas@monjalon.net=
> wrote:
>
> 28/03/2025 11:52, David Marchand:
> > --- a/lib/eal/common/eal_symbol_exports.h
> > +++ b/lib/eal/common/eal_symbol_exports.h
> > @@ -5,6 +5,8 @@
> >  #ifndef EAL_SYMBOL_EXPORTS_H
> >  #define EAL_SYMBOL_EXPORTS_H
> >
> > +#include <rte_common.h>
> > +
> >  /* Internal macros for exporting symbols, used by the build system.
> >   * For RTE_EXPORT_EXPERIMENTAL_SYMBOL, ver indicates the
> >   * version this symbol was introduced in.
> > @@ -13,4 +15,68 @@
> >  #define RTE_EXPORT_INTERNAL_SYMBOL(a)
> >  #define RTE_EXPORT_SYMBOL(a)
> >
> > +#if !defined(RTE_USE_FUNCTION_VERSIONING) && (defined(RTE_CC_GCC) || d=
efined(RTE_CC_CLANG))
> > +#define VERSIONING_WARN RTE_PRAGMA_WARNING(Use of function versioning =
disabled. \
> > +       Is "use_function_versioning=3Dtrue" in meson.build?)
> > +#else
> > +#define VERSIONING_WARN
> > +#endif
>
> Why no warning for other compilers?
> Why not warn at Meson level?

Symbol versioning is not functional with Windows compiler / linker atm.

When it is ready, the right warning mechanism can be implemented here.

>
> > +
> > +/*
> > + * Provides backwards compatibility when updating exported functions.
>
> I feel a word is missing. What "provides" it?

I'll reword.


>
> > + * When a symbol is exported from a library to provide an API, it also=
 provides a
> > + * calling convention (ABI) that is embodied in its name, return type,
> > + * arguments, etc.  On occasion that function may need to change to ac=
commodate
> > + * new functionality, behavior, etc.  When that occurs, it is desirabl=
e to
> > + * allow for backwards compatibility for a time with older binaries th=
at are
> > + * dynamically linked to the dpdk.
> > + */
> > +
> > +#ifdef RTE_BUILD_SHARED_LIB
> > +
> > +/*
>
> Why not Doxygen style?

Because this header is internal, and not parsed by Doxygen?


>
> > + * RTE_VERSION_SYMBOL
>
> No need to repeat the macro name here.
>
> > + * Creates a symbol version table entry binding symbol <name>@DPDK_<ve=
r> to the internal
>
> Imperative form is more usual.

Ack.

>
> > + * function name <name>_v<ver>.
> > + */
> > +#define RTE_VERSION_SYMBOL(ver, type, name, args) VERSIONING_WARN \
> > +__asm__(".symver " RTE_STR(name) "_v" RTE_STR(ver) ", " RTE_STR(name) =
"@DPDK_" RTE_STR(ver)); \
> > +__rte_used type name ## _v ## ver args; \
> > +type name ## _v ## ver args
>
> This is only GNU style. It should be highlighted both in this file and th=
e commit log.

Yes, I'll insist on this point in the commitlog.


--=20
David Marchand