---------------------------
System libraries usually adopt the familiar major and minor version naming
-convention, where major versions (e.g. ``librte_eal 20.x, 21.x``) are presumed
+convention, where major versions (e.g. ``librte_eal 21.x, 22.x``) are presumed
to be ABI incompatible with each other and minor versions (e.g. ``librte_eal
-20.1, 20.2``) are presumed to be ABI compatible. A library's `soname
+21.1, 21.2``) are presumed to be ABI compatible. A library's `soname
<https://en.wikipedia.org/wiki/Soname>`_. is typically used to provide backward
compatibility information about a given library, describing the lowest common
denominator ABI supported by the library. The soname or logical name for the
library, is typically comprised of the library's name and major version e.g.
-``librte_eal.so.20``.
+``librte_eal.so.21``.
During an application's build process, a library's soname is noted as a runtime
dependency of the application. This information is then used by the `dynamic
linker <https://en.wikipedia.org/wiki/Dynamic_linker>`_ when resolving the
applications dependencies at runtime, to load a library supporting the correct
ABI version. The library loaded at runtime therefore, may be a minor revision
-supporting the same major ABI version (e.g. ``librte_eal.20.2``), as the library
-used to link the application (e.g ``librte_eal.20.0``).
+supporting the same major ABI version (e.g. ``librte_eal.21.2``), as the library
+used to link the application (e.g ``librte_eal.21.0``).
.. _major_abi_versions:
.. code-block:: none
- $ head ./lib/librte_acl/rte_acl_version.map
- DPDK_20 {
+ $ head ./lib/acl/version.map
+ DPDK_21 {
global:
...
- $ head ./lib/librte_eal/rte_eal_version.map
- DPDK_20 {
+ $ head ./lib/eal/version.map
+ DPDK_21 {
global:
...
When an ABI change is made between major ABI versions to a given library, a new
section is added to that library's version map describing the impending new ABI
version, as described in the section :ref:`example_abi_macro_usage`. The
-library's soname and filename however do not change, e.g. ``libacl.so.20``, as
+library's soname and filename however do not change, e.g. ``libacl.so.21``, as
ABI compatibility with the last major ABI version continues to be preserved for
that library.
.. code-block:: none
- $ head ./lib/librte_acl/rte_acl_version.map
- DPDK_20 {
+ $ head ./lib/acl/version.map
+ DPDK_21 {
global:
...
- DPDK_21 {
+ DPDK_22 {
global:
- } DPDK_20;
+ } DPDK_21;
...
- $ head ./lib/librte_eal/rte_eal_version.map
- DPDK_20 {
+ $ head ./lib/eal/version.map
+ DPDK_21 {
global:
...
-However when a new ABI version is declared, for example DPDK ``21``, old
+However when a new ABI version is declared, for example DPDK ``22``, old
depreciated functions may be safely removed at this point and the entire old
major ABI version removed, see the section :ref:`deprecating_entire_abi` on
how this may be done.
.. code-block:: none
- $ head ./lib/librte_acl/rte_acl_version.map
- DPDK_21 {
+ $ head ./lib/acl/version.map
+ DPDK_22 {
global:
...
- $ head ./lib/librte_eal/rte_eal_version.map
- DPDK_21 {
+ $ head ./lib/eal/version.map
+ DPDK_22 {
global:
...
At the same time, the major ABI version is changed atomically across all
libraries by incrementing the major version in the ABI_VERSION file. This is
-done globally for all libraries that declare a stable ABI. For libraries marked
-as EXPERIMENTAL, their major ABI version is always set to 0.
+done globally for all libraries.
Minor ABI versions
~~~~~~~~~~~~~~~~~~
To support backward compatibility the ``rte_function_versioning.h``
header file provides macros to use when updating exported functions. These
-macros are used in conjunction with the ``rte_<library>_version.map`` file for
+macros are used in conjunction with the ``version.map`` file for
a given library to allow multiple versions of a symbol to exist in a shared
library so that older binaries need not be immediately recompiled.
``be`` to signal that it is being used as an implementation of a particular
version of symbol ``b``.
+* ``VERSION_SYMBOL_EXPERIMENTAL(b, e)``: Creates a symbol version table entry
+ binding versioned symbol ``b@EXPERIMENTAL`` to the internal function ``be``.
+ The macro is used when a symbol matures to become part of the stable ABI, to
+ provide an alias to experimental until the next major ABI version.
+
.. _example_abi_macro_usage:
Examples of ABI Macro use
Note also that, being a public function, the header file prototype must also be
changed, as must all the call sites, to reflect the new ABI footprint. We will
maintain previous ABI versions that are accessible only to previously compiled
-binaries
+binaries.
The addition of a parameter to the function is ABI breaking as the function is
public, and existing application may use it in its current form. However, the
.. code-block:: none
- DPDK_20 {
+ DPDK_21 {
global:
rte_acl_add_rules;
.. code-block:: none
- DPDK_20 {
+ DPDK_21 {
global:
rte_acl_add_rules;
local: *;
};
- DPDK_21 {
+ DPDK_22 {
global:
rte_acl_create;
- } DPDK_20;
+ } DPDK_21;
-The addition of the new block tells the linker that a new version node is
-available (DPDK_21), which contains the symbol rte_acl_create, and inherits
-the symbols from the DPDK_20 node. This list is directly translated into a
-list of exported symbols when DPDK is compiled as a shared library
+The addition of the new block tells the linker that a new version node
+``DPDK_22`` is available, which contains the symbol rte_acl_create, and inherits
+the symbols from the DPDK_21 node. This list is directly translated into a
+list of exported symbols when DPDK is compiled as a shared library.
-Next, we need to specify in the code which function map to the rte_acl_create
+Next, we need to specify in the code which function maps to the rte_acl_create
symbol at which versions. First, at the site of the initial symbol definition,
we need to update the function so that it is uniquely named, and not in conflict
with the public symbol name
-struct rte_acl_ctx *
-rte_acl_create(const struct rte_acl_param *param)
+struct rte_acl_ctx * __vsym
- +rte_acl_create_v20(const struct rte_acl_param *param)
+ +rte_acl_create_v21(const struct rte_acl_param *param)
{
size_t sz;
struct rte_acl_ctx *ctx;
...
Note that the base name of the symbol was kept intact, as this is conducive to
-the macros used for versioning symbols and we have annotated the function as an
-implementation of versioned symbol. That is our next step, mapping this new
-symbol name to the initial symbol name at version node 20. Immediately after
-the function, we add this line of code
+the macros used for versioning symbols and we have annotated the function as
+``__vsym``, an implementation of a versioned symbol . That is our next step,
+mapping this new symbol name to the initial symbol name at version node 21.
+Immediately after the function, we add the VERSION_SYMBOL macro.
.. code-block:: c
- VERSION_SYMBOL(rte_acl_create, _v20, 20);
+ #include <rte_function_versioning.h>
+
+ ...
+ VERSION_SYMBOL(rte_acl_create, _v21, 21);
Remembering to also add the rte_function_versioning.h header to the requisite c
-file where these changes are being made. The above macro instructs the linker to
-create a new symbol ``rte_acl_create@DPDK_20``, which matches the symbol created
+file where these changes are being made. The macro instructs the linker to
+create a new symbol ``rte_acl_create@DPDK_21``, which matches the symbol created
in older builds, but now points to the above newly named function. We have now
mapped the original rte_acl_create symbol to the original function (but with a
new name).
-Next, we need to create the 21 version of the symbol. We create a new function
-name, with a different suffix, and implement it appropriately
+Please see the section :ref:`Enabling versioning macros
+<enabling_versioning_macros>` to enable this macro in the meson/ninja build.
+Next, we need to create the new ``v22`` version of the symbol. We create a new
+function name, with the ``v22`` suffix, and implement it appropriately.
.. code-block:: c
struct rte_acl_ctx * __vsym
- rte_acl_create_v21(const struct rte_acl_param *param, int debug);
+ rte_acl_create_v22(const struct rte_acl_param *param, int debug);
{
- struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
+ struct rte_acl_ctx *ctx = rte_acl_create_v21(param);
ctx->debug = debug;
}
This code serves as our new API call. Its the same as our old call, but adds the
-new parameter in place. Next we need to map this function to the symbol
-``rte_acl_create@DPDK_21``. To do this, we modify the public prototype of the
-call in the header file, adding the macro there to inform all including
-applications, that on re-link, the default rte_acl_create symbol should point to
-this function. Note that we could do this by simply naming the function above
-rte_acl_create, and the linker would chose the most recent version tag to apply
-in the version script, but we can also do this in the header file
+new parameter in place. Next we need to map this function to the new default
+symbol ``rte_acl_create@DPDK_22``. To do this, immediately after the function,
+we add the BIND_DEFAULT_SYMBOL macro.
+
+.. code-block:: c
+
+ #include <rte_function_versioning.h>
+
+ ...
+ BIND_DEFAULT_SYMBOL(rte_acl_create, _v22, 22);
+
+The macro instructs the linker to create the new default symbol
+``rte_acl_create@DPDK_22``, which points to the above newly named function.
+
+We finally modify the prototype of the call in the public header file,
+such that it contains both versions of the symbol and the public API.
.. code-block:: c
struct rte_acl_ctx *
- -rte_acl_create(const struct rte_acl_param *param);
- +rte_acl_create_v21(const struct rte_acl_param *param, int debug);
- +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 21);
-
-The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
-header, to link to the rte_acl_create_v21 function and apply the DPDK_21
-version node to it. This method is more explicit and flexible than just
-re-implementing the exact symbol name, and allows for other features (such as
-linking to the old symbol version by default, when the new ABI is to be opt-in
-for a period.
-
-One last thing we need to do. Note that we've taken what was a public symbol,
-and duplicated it into two uniquely and differently named symbols. We've then
-mapped each of those back to the public symbol ``rte_acl_create`` with different
-version tags. This only applies to dynamic linking, as static linking has no
-notion of versioning. That leaves this code in a position of no longer having a
-symbol simply named ``rte_acl_create`` and a static build will fail on that
-missing symbol.
+ rte_acl_create(const struct rte_acl_param *param);
+
+ struct rte_acl_ctx * __vsym
+ rte_acl_create_v21(const struct rte_acl_param *param);
+
+ struct rte_acl_ctx * __vsym
+ rte_acl_create_v22(const struct rte_acl_param *param, int debug);
+
+
+And that's it, on the next shared library rebuild, there will be two versions of
+rte_acl_create, an old DPDK_21 version, used by previously built applications,
+and a new DPDK_22 version, used by future built applications.
+
+.. note::
+
+ **Before you leave**, please take care reviewing the sections on
+ :ref:`mapping static symbols <mapping_static_symbols>`,
+ :ref:`enabling versioning macros <enabling_versioning_macros>`,
+ and :ref:`ABI deprecation <abi_deprecation>`.
+
+
+.. _mapping_static_symbols:
+
+Mapping static symbols
+______________________
+
+Now we've taken what was a public symbol, and duplicated it into two uniquely
+and differently named symbols. We've then mapped each of those back to the
+public symbol ``rte_acl_create`` with different version tags. This only applies
+to dynamic linking, as static linking has no notion of versioning. That leaves
+this code in a position of no longer having a symbol simply named
+``rte_acl_create`` and a static build will fail on that missing symbol.
To correct this, we can simply map a function of our choosing back to the public
symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro. Generally the
assumption is that the most recent version of the symbol is the one you want to
-map. So, back in the C file where, immediately after ``rte_acl_create_v21`` is
+map. So, back in the C file where, immediately after ``rte_acl_create_v22`` is
defined, we add this
.. code-block:: c
struct rte_acl_ctx * __vsym
- rte_acl_create_v21(const struct rte_acl_param *param, int debug)
+ rte_acl_create_v22(const struct rte_acl_param *param, int debug)
{
...
}
- MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
+ MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v22);
That tells the compiler that, when building a static library, any calls to the
-symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
+symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v22``
+
+
+.. _enabling_versioning_macros:
+
+Enabling versioning macros
+__________________________
+
+Finally, we need to indicate to the :doc:`meson/ninja build system
+<../prog_guide/build-sdk-meson>` to enable versioning macros when building the
+library or driver. In the libraries or driver where we have added symbol
+versioning, in the ``meson.build`` file we add the following
-That's it, on the next shared library rebuild, there will be two versions of
-rte_acl_create, an old DPDK_20 version, used by previously built applications,
-and a new DPDK_21 version, used by future built applications.
+.. code-block:: none
+
+ use_function_versioning = true
+
+at the start of the head of the file. This will indicate to the tool-chain to
+enable the function version macros when building.
+
+
+.. _aliasing_experimental_symbols:
+
+Aliasing experimental symbols
+_____________________________
+
+In situations in which an ``experimental`` symbol has been stable for some time,
+and it becomes a candidate for promotion to the stable ABI. At this time, when
+promoting the symbol, the maintainer may choose to provide an alias to the
+``experimental`` symbol version, so as not to break consuming applications.
+This alias is then dropped in the next major ABI version.
+
+The process to provide an alias to ``experimental`` is similar to that, of
+:ref:`symbol versioning <example_abi_macro_usage>` described above.
+Assume we have an experimental function ``rte_acl_create`` as follows:
+
+.. code-block:: c
+
+ #include <rte_compat.h>
+
+ /*
+ * Create an acl context object for apps to
+ * manipulate
+ */
+ __rte_experimental
+ struct rte_acl_ctx *
+ rte_acl_create(const struct rte_acl_param *param)
+ {
+ ...
+ }
+
+In the map file, experimental symbols are listed as part of the ``EXPERIMENTAL``
+version node.
+
+.. code-block:: none
+
+ DPDK_21 {
+ global:
+ ...
+ local: *;
+ };
+
+ EXPERIMENTAL {
+ global:
+
+ rte_acl_create;
+ };
+
+When we promote the symbol to the stable ABI, we simply strip the
+``__rte_experimental`` annotation from the function and move the symbol from the
+``EXPERIMENTAL`` node, to the node of the next major ABI version as follow.
+
+.. code-block:: c
+
+ /*
+ * Create an acl context object for apps to
+ * manipulate
+ */
+ struct rte_acl_ctx *
+ rte_acl_create(const struct rte_acl_param *param)
+ {
+ ...
+ }
+
+We then update the map file, adding the symbol ``rte_acl_create``
+to the ``DPDK_22`` version node.
+
+.. code-block:: none
+
+ DPDK_21 {
+ global:
+ ...
+
+ local: *;
+ };
+
+ DPDK_22 {
+ global:
+
+ rte_acl_create;
+ } DPDK_21;
+
+
+Although there are strictly no guarantees or commitments associated with
+:ref:`experimental symbols <experimental_apis>`, a maintainer may wish to offer
+an alias to experimental. The process to add an alias to experimental,
+is similar to the symbol versioning process. Assuming we have an experimental
+symbol as before, we now add the symbol to both the ``EXPERIMENTAL``
+and ``DPDK_22`` version nodes.
+
+.. code-block:: c
+
+ #include <rte_compat.h>;
+ #include <rte_function_versioning.h>
+
+ /*
+ * Create an acl context object for apps to
+ * manipulate
+ */
+ struct rte_acl_ctx *
+ rte_acl_create(const struct rte_acl_param *param)
+ {
+ ...
+ }
+
+ __rte_experimental
+ struct rte_acl_ctx *
+ rte_acl_create_e(const struct rte_acl_param *param)
+ {
+ return rte_acl_create(param);
+ }
+ VERSION_SYMBOL_EXPERIMENTAL(rte_acl_create, _e);
+
+ struct rte_acl_ctx *
+ rte_acl_create_v22(const struct rte_acl_param *param)
+ {
+ return rte_acl_create(param);
+ }
+ BIND_DEFAULT_SYMBOL(rte_acl_create, _v22, 22);
+
+In the map file, we map the symbol to both the ``EXPERIMENTAL``
+and ``DPDK_22`` version nodes.
+
+.. code-block:: none
+
+ DPDK_21 {
+ global:
+ ...
+
+ local: *;
+ };
+
+ DPDK_22 {
+ global:
+
+ rte_acl_create;
+ } DPDK_21;
+
+ EXPERIMENTAL {
+ global:
+
+ rte_acl_create;
+ };
+
+.. note::
+
+ Please note, similar to :ref:`symbol versioning <example_abi_macro_usage>`,
+ when aliasing to experimental you will also need to take care of
+ :ref:`mapping static symbols <mapping_static_symbols>`.
+
+
+.. _abi_deprecation:
Deprecating part of a public API
________________________________
-Lets assume that you've done the above update, and in preparation for the next
+Lets assume that you've done the above updates, and in preparation for the next
major ABI version you decide you would like to retire the old version of the
function. After having gone through the ABI deprecation announcement process,
removal is easy. Start by removing the symbol from the requisite version map
.. code-block:: none
- DPDK_20 {
+ DPDK_21 {
global:
rte_acl_add_rules;
local: *;
};
- DPDK_21 {
+ DPDK_22 {
global:
rte_acl_create;
- } DPDK_20;
+ } DPDK_21;
Next remove the corresponding versioned export.
.. code-block:: c
- -VERSION_SYMBOL(rte_acl_create, _v20, 20);
+ -VERSION_SYMBOL(rte_acl_create, _v21, 21);
Note that the internal function definition could also be removed, but its used
-in our example by the newer version v21, so we leave it in place and declare it
-as static. This is a coding style choice.
+in our example by the newer version ``v22``, so we leave it in place and declare
+it as static. This is a coding style choice.
.. _deprecating_entire_abi:
.. code-block:: none
- DPDK_21 {
+ DPDK_22 {
global:
rte_acl_add_rules;
.. code-block:: c
- -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 20);
- +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 21);
+ -BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 21);
+ +BIND_DEFAULT_SYMBOL(rte_acl_create, _v22, 22);
-Lastly, any VERSION_SYMBOL macros that point to the old version node should be
-removed, taking care to keep, where need old code in place to support newer
-versions of the symbol.
+Lastly, any VERSION_SYMBOL macros that point to the old version nodes
+should be removed, taking care to preserve any code that is shared
+with the new version node.
Running the ABI Validator
-------------------------
The ``devtools`` directory in the DPDK source tree contains a utility program,
-``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
-Compliance Checker
-<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
-
-This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
-utilities which can be installed via a package manager. For example::
-
- sudo yum install abi-compliance-checker
- sudo yum install abi-dumper
-
-The syntax of the ``validate-abi.sh`` utility is::
-
- ./devtools/validate-abi.sh <REV1> <REV2>
-
-Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
-https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
-on the local repo.
-
-For example::
-
- # Check between the previous and latest commit:
- ./devtools/validate-abi.sh HEAD~1 HEAD
-
- # Check on a specific compilation target:
- ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
+``check-abi.sh``, for validating the DPDK ABI based on the libabigail
+`abidiff utility <https://sourceware.org/libabigail/manual/abidiff.html>`_.
- # Check between two tags:
- ./devtools/validate-abi.sh v2.0.0 v2.1.0
+The syntax of the ``check-abi.sh`` utility is::
- # Check between git master and local topic-branch "vhost-hacking":
- ./devtools/validate-abi.sh master vhost-hacking
+ devtools/check-abi.sh <refdir> <newdir>
-After the validation script completes (it can take a while since it need to
-compile both tags) it will create compatibility reports in the
-``./abi-check/compat_report`` directory. Listed incompatibilities can be found
-as follows::
+Where <refdir> specifies the directory housing the reference build of DPDK,
+and <newdir> specifies the DPDK build directory to check the ABI of.
- grep -lr Incompatible abi-check/compat_reports/
+The ABI compatibility is automatically verified when using a build script
+from ``devtools``, if the variable ``DPDK_ABI_REF_VERSION`` is set with a tag,
+as described in :ref:`ABI check recommendations<integrated_abi_check>`.