[dpdk-dev] [PATCH 1/4] compat: Add infrastructure to support symbol versioning
Neil Horman
nhorman at tuxdriver.com
Tue Sep 23 16:58:29 CEST 2014
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
> > +#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
>
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