[dpdk-dev] [PATCH 1/4] compat: Add infrastructure to support symbol versioning

[Sergio Gonzalez Monroy]

On Tue, Sep 23, 2014 at 10:58:29AM -0400, Neil Horman wrote:
> On Tue, Sep 23, 2014 at 11:39:29AM +0100, Sergio Gonzalez Monroy wrote:
> > Hi Neil,
> > 
> > On Mon, Sep 15, 2014 at 03:23:48PM -0400, Neil Horman wrote:
> > > Add initial pass header files to support symbol versioning.
> > > 
> > > Signed-off-by: Neil Horman <nhorman at tuxdriver.com>
> > > CC: Thomas Monjalon <thomas.monjalon at 6wind.com>
> > > CC: "Richardson, Bruce" <bruce.richardson at intel.com>
> > > ---
> > >  lib/Makefile                   |  1 +
> > >  lib/librte_compat/Makefile     | 38 +++++++++++++++++++
> > >  lib/librte_compat/rte_compat.h | 86 ++++++++++++++++++++++++++++++++++++++++++
> > >  mk/rte.lib.mk                  |  6 +++
> > >  4 files changed, 131 insertions(+)
> > >  create mode 100644 lib/librte_compat/Makefile
> > >  create mode 100644 lib/librte_compat/rte_compat.h
> > > 
> > > diff --git a/lib/Makefile b/lib/Makefile
> > > index 10c5bb3..a85b55b 100644
> > > --- a/lib/Makefile
> > > +++ b/lib/Makefile
> > > @@ -32,6 +32,7 @@
> > >  include $(RTE_SDK)/mk/rte.vars.mk
> > >  
> > >  DIRS-$(CONFIG_RTE_LIBC) += libc
> > > +DIRS-y += librte_compat
> > >  DIRS-$(CONFIG_RTE_LIBRTE_EAL) += librte_eal
> > >  DIRS-$(CONFIG_RTE_LIBRTE_MALLOC) += librte_malloc
> > >  DIRS-$(CONFIG_RTE_LIBRTE_RING) += librte_ring
> > > diff --git a/lib/librte_compat/Makefile b/lib/librte_compat/Makefile
> > > new file mode 100644
> > > index 0000000..a61511a
> > > --- /dev/null
> > > +++ b/lib/librte_compat/Makefile
> > > @@ -0,0 +1,38 @@
> > > +#   BSD LICENSE
> > > +#
> > > +#   Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
> > > +#   All rights reserved.
> > > +#
> > > +#   Redistribution and use in source and binary forms, with or without
> > > +#   modification, are permitted provided that the following conditions
> > > +#   are met:
> > > +#
> > > +#     * Redistributions of source code must retain the above copyright
> > > +#       notice, this list of conditions and the following disclaimer.
> > > +#     * Redistributions in binary form must reproduce the above copyright
> > > +#       notice, this list of conditions and the following disclaimer in
> > > +#       the documentation and/or other materials provided with the
> > > +#       distribution.
> > > +#     * Neither the name of Intel Corporation nor the names of its
> > > +#       contributors may be used to endorse or promote products derived
> > > +#       from this software without specific prior written permission.
> > > +#
> > > +#   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
> > > +#   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
> > > +#   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
> > > +#   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
> > > +#   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
> > > +#   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
> > > +#   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
> > > +#   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
> > > +#   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> > > +#   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
> > > +#   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> > > +
> > > +include $(RTE_SDK)/mk/rte.vars.mk
> > > +
> > > +
> > > +# install includes
> > > +SYMLINK-y-include := rte_compat.h
> > > +
> > > +include $(RTE_SDK)/mk/rte.lib.mk
> > > diff --git a/lib/librte_compat/rte_compat.h b/lib/librte_compat/rte_compat.h
> > > new file mode 100644
> > > index 0000000..6d65a53
> > > --- /dev/null
> > > +++ b/lib/librte_compat/rte_compat.h
> > > @@ -0,0 +1,86 @@
> > > +/*-
> > > + *   BSD LICENSE
> > > + *
> > > + *   Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
> > > + *   All rights reserved.
> > > + *
> > > + *   Redistribution and use in source and binary forms, with or without
> > > + *   modification, are permitted provided that the following conditions
> > > + *   are met:
> > > + *
> > > + *     * Redistributions of source code must retain the above copyright
> > > + *       notice, this list of conditions and the following disclaimer.
> > > + *     * Redistributions in binary form must reproduce the above copyright
> > > + *       notice, this list of conditions and the following disclaimer in
> > > + *       the documentation and/or other materials provided with the
> > > + *       distribution.
> > > + *     * Neither the name of Intel Corporation nor the names of its
> > > + *       contributors may be used to endorse or promote products derived
> > > + *       from this software without specific prior written permission.
> > > + *
> > > + *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
> > > + *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
> > > + *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
> > > + *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
> > > + *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
> > > + *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
> > > + *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
> > > + *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
> > > + *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> > > + *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
> > > + *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> > > + */
> > > +
> > > +#ifndef _RTE_COMPAT_H_
> > > +#define _RTE_COMPAT_H_
> > > +
> > > +/*
> > > + * This is just a stringification macro for use below.
> > > + */
> > > +#define SA(x) #x
> > > +
> > > +#ifdef RTE_SYMBOL_VERSIONING
> > > +
> > > +/*
> > > + * Provides backwards compatibility when updating exported functions.
> > > + * When a symol 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 accomodate
> > > + * new functionality, behavior, etc.  When that occurs, it is desireable to
> > > + * allow for backwards compatibility for a time with older binaries that are
> > > + * dynamically linked to the dpdk.  to support that the __vsym and
> > > + * VERSION_SYMBOL macros are created.  They, in conjunction with the
> > > + * <library>_version.map file for a given library allow for multiple versions of
> > > + * a symbol to exist in a shared library so that older binaries need not be
> > > + * immediately recompiled. Their use is outlined in the following example:
> > > + * Assumptions: DPDK 1.(X) contains a function int foo(char *string)
> > > + *              DPDK 1.(X+1) needs to change foo to be int foo(int index)
> > > + *
> > > + * To accomplish this:
> > > + * 1) Edit lib/<library>/library_version.map to add a DPDK_1.8 node, in which
> > > + * foo is exported as a global symbol
> > > + *
> > > + * 2) rename the existing function int foo(char *string) to 
> > > + * 	int __vsym foo_v18(char *string)
> > > + *
> > > + * 3) Add this macro immediately below the function
> > > + * 	VERSION_SYMBOL(foo, _v18, 1.8);
> > > + *
> > > + */
> > > +#define VERSION_SYMBOL(b, e, v) __asm__(".symver " SA(b) SA(e) ", "SA(b)"@DPDK_"SA(v))
> > > +#define __vsym __attribute__((used))
> > > +
> > 
> > I may be missing something here but would it not be neccessary to define a
> > default symbol?
> > Otherwise there would be multiple definitions of a given symbol and the linker
> > won't know which symbol version to bind to.
> > 
> > Following your example, something along these lines:
> >  4) Edit lib/<library>/library_version.map to add a DPDK_1.9 node that is a
> >    successor to DPDK_1.8, in which foo is exported as a global symbol 
> >    DPDK_1.9 {
> >       global: foo;
> >    } DPDK_1.8;
> > 
> >  5) rename new function int foo(int index) to
> >    int __vsym foo_v19(int index)
> > 
> >  6) Add this macro immediately below the function:
> >    DEFAULT_SYMBOL(foo, _v19, 1.9);
> > 
> > #define DEFAULT_SYMBOL(b, e, v) __asm__(".symver " SA(b) SA(e) ", "SA(b)"@@DPDK_"SA(v))
> > 
> 
> You're spot on (though the macro that I created in rte_compat.h is
> VERSION_SYMBOL).  
> 
> When you use a version script to create a DSO, at link time, the appropriate
> version is appended to the symbol name (you can see it with objdump -t in a
> linked binary).  If you want to update the symbol to a new version, you do what
> I documented in the header file (though now that I re-read it, it could be more
> clear.  Hows this for a change to the documentation:
> 
> To make a new version of a function foo in a DSO:
> 
> 1) Edit lib/<library>/library_version.map to add a DPDK_1.8 node, in which
>    foo is exported as a global symbol
> 
> 2) rename the existing function int foo(char *string) to 
>    int __vsym foo_v18(char *string)
> 
> 3) Add this macro immediately below the function
>    VERSION_SYMBOL(foo, _v18, 1.8);
> 
> 4) Implement the new version of the function foo.
> 
> 
> Those steps above will create two symbols in your export table of the DSO:
> 
> foo@@DPDK_1.8
> foo@@DPDK_1.9
> 
> Any application linked against this DSO will link against the latest version
> (DPDK_1.9).  But if you look at the symbols referenced in a binary linked
> against an older version of the same DSO, you'll note they explicitly look for
> foo@@DPDK_1.8.  Thats how we provide backwards compatibility
> 
> Does that answer your questions?
> 
> Neil
> 
Correct me if I am wrong but when we define multiple versions of a symbol we
need to specify a default one.
As an example, if we were to have three versions of foo the export table of the
DSO should look something like this:

foo at VER_1.0
foo at VER_1.1
foo@@VER_1.2

In the above example, foo VER_1.2 is the default one and is indicated by
having double @.

Effectively we would need two macros VERSION_SYMBOL and DEFAULT_VERSION_SYMBOL
(maybe this name is more appropriate).

#define VERSION_SYMBOL(b, e, v)         \
    __asm__(".symver " SA(b) SA(e) ", "SA(b)"@DPDK_"SA(v))
#define DEFAULT_VERSION_SYMBOL(b, e, v) \
    __asm__(".symver " SA(b) SA(e) ", "SA(b)"@@DPDK_"SA(v))

Following on the example, we should have something like:

   int __vsym foo_v18(char *string) {...}
   VERSION_SYMBOL(foo, _v18, 1.8);

   int __vsym foo_v19(int index) {...}
   DEFAULT_VERSION_SYMBOL(foo, _v19, 1.9);

The DSO export table would have the following symbols:

   foo at DPDK_1.8
   foo@@DPDK_1.9

Old binaries linked against DPDK 1.8 would have references to:
foo@@DPDK_1.8

and new binaries linked against DPDK 1.9 would have to:
foo@@DPDK_1.9

Sergio

> > > +#else
> > > +/*
> > > + * No symbol versioning in use
> > > + */
> > > +#define VERSION_SYMBOL(b, e, v)
> > > +#define __vsym
> > > +
> > > +/*
> > > + * RTE_SYMBOL_VERSIONING
> > > + */
> > > +#endif
> > > +
> > > +
> > > +#endif /* _RTE_COMPAT_H_ */
> > > diff --git a/mk/rte.lib.mk b/mk/rte.lib.mk
> > > index f458258..82ac309 100644
> > > --- a/mk/rte.lib.mk
> > > +++ b/mk/rte.lib.mk
> > > @@ -40,8 +40,12 @@ VPATH += $(SRCDIR)
> > >  
> > >  ifeq ($(RTE_BUILD_SHARED_LIB),y)
> > >  LIB := $(patsubst %.a,%.so,$(LIB))
> > > +
> > > +CPU_LDFLAGS += --version-script=$(EXPORT_MAP)
> > > +
> > >  endif
> > >  
> > > +
> > >  _BUILD = $(LIB)
> > >  _INSTALL = $(INSTALL-FILES-y) $(SYMLINK-FILES-y) $(RTE_OUTPUT)/lib/$(LIB)
> > >  _CLEAN = doclean
> > > @@ -160,7 +164,9 @@ endif
> > >  $(RTE_OUTPUT)/lib/$(LIB): $(LIB)
> > >  	@echo "  INSTALL-LIB $(LIB)"
> > >  	@[ -d $(RTE_OUTPUT)/lib ] || mkdir -p $(RTE_OUTPUT)/lib
> > > +ifneq ($(LIB),)
> > >  	$(Q)cp -f $(LIB) $(RTE_OUTPUT)/lib
> > > +endif
> > >  
> > >  #
> > >  # Clean all generated files
> > > -- 
> > > 1.9.3
> > > 
> > 
> > Sergio
> >