[dpdk-dev] [PATCH v4 1/4] doc: separate versioning.rst into version and policy
Ray Kinsella
mdr at ashroe.eu
Fri Sep 27 18:43:26 CEST 2019
On 27/09/2019 16:43, Aaron Conole wrote:
> Ray Kinsella <mdr at ashroe.eu> writes:
>
>> Separate versioning.rst into abi versioning and abi policy guidance, in
>> preparation for adding more detail to the abi policy.
>>
>> Signed-off-by: Ray Kinsella <mdr at ashroe.eu>
>> ---
>> doc/guides/contributing/abi_policy.rst | 169 +++++++++
>> doc/guides/contributing/abi_versioning.rst | 427 +++++++++++++++++++++
>> doc/guides/contributing/index.rst | 3 +-
>> doc/guides/contributing/versioning.rst | 591 -----------------------------
>> 4 files changed, 598 insertions(+), 592 deletions(-)
>> create mode 100644 doc/guides/contributing/abi_policy.rst
>> create mode 100644 doc/guides/contributing/abi_versioning.rst
>> delete mode 100644 doc/guides/contributing/versioning.rst
>>
>> diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
>> new file mode 100644
>> index 0000000..55bacb4
>> --- /dev/null
>> +++ b/doc/guides/contributing/abi_policy.rst
>> @@ -0,0 +1,169 @@
>> +.. SPDX-License-Identifier: BSD-3-Clause
>> + Copyright 2018 The DPDK contributors
>> +
>> +.. abi_api_policy:
>> +
>> +DPDK ABI/API policy
>> +===================
>> +
>> +Description
>> +-----------
>> +
>> +This document details some methods for handling ABI management in the DPDK.
>> +
>> +General Guidelines
>> +------------------
>> +
>> +#. Whenever possible, ABI should be preserved
>> +#. ABI/API may be changed with a deprecation process
>> +#. The modification of symbols can generally be managed with versioning
>> +#. Libraries or APIs marked in ``experimental`` state may change without constraint
>> +#. New APIs will be marked as ``experimental`` for at least one release to allow
>> + any issues found by users of the new API to be fixed quickly
>> +#. The addition of symbols is generally not problematic
>> +#. The removal of symbols generally is an ABI break and requires bumping of the
>> + LIBABIVER macro
>> +#. Updates to the minimum hardware requirements, which drop support for hardware which
>> + was previously supported, should be treated as an ABI change.
>> +
>> +What is an ABI
>> +~~~~~~~~~~~~~~
>> +
>> +An ABI (Application Binary Interface) is the set of runtime interfaces exposed
>> +by a library. It is similar to an API (Application Programming Interface) but
>> +is the result of compilation. It is also effectively cloned when applications
>> +link to dynamic libraries. That is to say when an application is compiled to
>> +link against dynamic libraries, it is assumed that the ABI remains constant
>> +between the time the application is compiled/linked, and the time that it runs.
>> +Therefore, in the case of dynamic linking, it is critical that an ABI is
>> +preserved, or (when modified), done in such a way that the application is unable
>> +to behave improperly or in an unexpected fashion.
>> +
>
> This section probably needs a bit more details. People still are
> confused what exactly constitutes ABI vs. API (see
> http://mails.dpdk.org/archives/dev/2018-January/085209.html for a
> confusing example).
>
> It's important that people know not just function signatures, but also
> return codes, and even data structure layouts are all part of the ABI.
Hi Aaron, just saw this now after I sent the v5.
This text is actually from the original policy, this patch is just
separating the abi policy from the abi versioning.
That said, I think another diagram would also be helpful here.
I have one we can use.
>
>> +
>> +ABI/API Deprecation
>> +-------------------
>> +
>> +The DPDK ABI policy
>> +~~~~~~~~~~~~~~~~~~~
>> +
>> +ABI versions are set at the time of major release labeling, and the ABI may
>> +change multiple times, without warning, between the last release label and the
>> +HEAD label of the git tree.
>> +
>> +ABI versions, once released, are available until such time as their
>> +deprecation has been noted in the Release Notes for at least one major release
>> +cycle. For example consider the case where the ABI for DPDK 2.0 has been
>> +shipped and then a decision is made to modify it during the development of
>> +DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
>> +release and the modification will be made available in the DPDK 2.2 release.
>> +
>> +ABI versions may be deprecated in whole or in part as needed by a given
>> +update.
>> +
>> +Some ABI changes may be too significant to reasonably maintain multiple
>> +versions. In those cases ABI's may be updated without backward compatibility
>> +being provided. The requirements for doing so are:
>> +
>> +#. At least 3 acknowledgments of the need to do so must be made on the
>> + dpdk.org mailing list.
>> +
>> + - The acknowledgment of the maintainer of the component is mandatory, or if
>> + no maintainer is available for the component, the tree/sub-tree maintainer
>> + for that component must acknowledge the ABI change instead.
>> +
>> + - It is also recommended that acknowledgments from different "areas of
>> + interest" be sought for each deprecation, for example: from NIC vendors,
>> + CPU vendors, end-users, etc.
>> +
>> +#. The changes (including an alternative map file) can be included with
>> + deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
>> + to provide more details about oncoming changes.
>> + ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
>> + More preferred way to provide this information is sending the feature
>> + as a separate patch and reference it in deprecation notice.
>> +
>> +#. A full deprecation cycle, as explained above, must be made to offer
>> + downstream consumers sufficient warning of the change.
>> +
>> +Note that the above process for ABI deprecation should not be undertaken
>> +lightly. ABI stability is extremely important for downstream consumers of the
>> +DPDK, especially when distributed in shared object form. Every effort should
>> +be made to preserve the ABI whenever possible. The ABI should only be changed
>> +for significant reasons, such as performance enhancements. ABI breakage due to
>> +changes such as reorganizing public structure fields for aesthetic or
>> +readability purposes should be avoided.
>> +
>> +.. note::
>> +
>> + Updates to the minimum hardware requirements, which drop support for hardware
>> + which was previously supported, should be treated as an ABI change, and
>> + follow the relevant deprecation policy procedures as above: 3 acks and
>> + announcement at least one release in advance.
>> +
>> +Examples of Deprecation Notices
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> +
>> +The following are some examples of ABI deprecation notices which would be
>> +added to the Release Notes:
>> +
>> +* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
>> + to be replaced with the inline function ``rte_foo()``.
>> +
>> +* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
>> + in version 2.0. Backwards compatibility will be maintained for this function
>> + until the release of version 2.1
>> +
>> +* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
>> + performance reasons. Existing binary applications will have backwards
>> + compatibility in release 2.0, while newly built binaries will need to
>> + reference the new structure variant ``struct rte_foo2``. Compatibility will
>> + be removed in release 2.2, and all applications will require updating and
>> + rebuilding to the new structure at that time, which will be renamed to the
>> + original ``struct rte_foo``.
>> +
>> +* Significant ABI changes are planned for the ``librte_dostuff`` library. The
>> + upcoming release 2.0 will not contain these changes, but release 2.1 will,
>> + and no backwards compatibility is planned due to the extensive nature of
>> + these changes. Binaries using this library built prior to version 2.1 will
>> + require updating and recompilation.
>> +
>> +New API replacing previous one
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> +
>> +If a new API proposed functionally replaces an existing one, when the new API
>> +becomes non-experimental then the old one is marked with ``__rte_deprecated``.
>> +Deprecated APIs are removed completely just after the next LTS.
>> +
>> +Reminder that old API should follow deprecation process to be removed.
>> +
>> +
>> +Experimental APIs
>> +-----------------
>> +
>> +APIs marked as ``experimental`` are not considered part of the ABI and may
>> +change without warning at any time. Since changes to APIs are most likely
>> +immediately after their introduction, as users begin to take advantage of
>> +those new APIs and start finding issues with them, new DPDK APIs will be
>> +automatically marked as ``experimental`` to allow for a period of stabilization
>> +before they become part of a tracked ABI.
>> +
>> +Note that marking an API as experimental is a multi step process.
>> +To mark an API as experimental, the symbols which are desired to be exported
>> +must be placed in an EXPERIMENTAL version block in the corresponding libraries'
>> +version map script.
>> +Secondly, the corresponding prototypes of those exported functions (in the
>> +development header files), must be marked with the ``__rte_experimental`` tag
>> +(see ``rte_compat.h``).
>> +The DPDK build makefiles perform a check to ensure that the map file and the
>> +C code reflect the same list of symbols.
>> +This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
>> +during compilation in the corresponding library Makefile.
>> +
>> +In addition to tagging the code with ``__rte_experimental``,
>> +the doxygen markup must also contain the EXPERIMENTAL string,
>> +and the MAINTAINERS file should note the EXPERIMENTAL libraries.
>> +
>> +For removing the experimental tag associated with an API, deprecation notice
>> +is not required. Though, an API should remain in experimental state for at least
>> +one release. Thereafter, normal process of posting patch for review to mailing
>> +list can be followed.
>> diff --git a/doc/guides/contributing/abi_versioning.rst b/doc/guides/contributing/abi_versioning.rst
>> new file mode 100644
>> index 0000000..53e6ac0
>> --- /dev/null
>> +++ b/doc/guides/contributing/abi_versioning.rst
>> @@ -0,0 +1,427 @@
>> +.. SPDX-License-Identifier: BSD-3-Clause
>> + Copyright 2018 The DPDK contributors
>> +
>> +.. library_versioning:
>> +
>> +Library versioning
>> +------------------
>> +
>> +Downstreams might want to provide different DPDK releases at the same time to
>> +support multiple consumers of DPDK linked against older and newer sonames.
>> +
>> +Also due to the interdependencies that DPDK libraries can have applications
>> +might end up with an executable space in which multiple versions of a library
>> +are mapped by ld.so.
>> +
>> +Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
>> +depending on LibA.
>> +
>> +.. note::
>> +
>> + Application
>> + \-> LibA.old
>> + \-> LibB.new -> LibA.new
>> +
>> +That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
>> +If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
>> +library - versions defined in the libraries ``LIBABIVER``.
>> +An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
>> +``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
>> +
>> +
>> +ABI versioning
>> +--------------
>> +
>> +Versioning Macros
>> +~~~~~~~~~~~~~~~~~
>> +
>> +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 and
>> +arguments. Occasionally that function may need to change to accommodate new
>> +functionality or behavior. When that occurs, it is desirable to allow for
>> +backward compatibility for a time with older binaries that are dynamically
>> +linked to the DPDK.
>> +
>> +To support backward compatibility the ``rte_compat.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
>> +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.
>> +
>> +The macros exported are:
>> +
>> +* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
>> + versioned symbol ``b at DPDK_n`` to the internal function ``b_e``.
>> +
>> +* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
>> + the linker to bind references to symbol ``b`` to the internal symbol
>> + ``b_e``.
>> +
>> +* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
>> + fully qualified function ``p``, so that if a symbol becomes versioned, it
>> + can still be mapped back to the public symbol name.
>> +
>> +Examples of ABI Macro use
>> +^^^^^^^^^^^^^^^^^^^^^^^^^
>> +
>> +Updating a public API
>> +_____________________
>> +
>> +Assume we have a function as follows
>> +
>> +.. 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)
>> + {
>> + ...
>> + }
>> +
>> +
>> +Assume that struct rte_acl_ctx is a private structure, and that a developer
>> +wishes to enhance the acl api so that a debugging flag can be enabled on a
>> +per-context basis. This requires an addition to the structure (which, being
>> +private, is safe), but it also requires modifying the code as follows
>> +
>> +.. 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, int debug)
>> + {
>> + ...
>> + }
>> +
>> +
>> +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
>> +
>> +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
>> +compatibility macros in DPDK allow a developer to use symbol versioning so that
>> +multiple functions can be mapped to the same public symbol based on when an
>> +application was linked to it. To see how this is done, we start with the
>> +requisite libraries version map file. Initially the version map file for the
>> +acl library looks like this
>> +
>> +.. code-block:: none
>> +
>> + DPDK_2.0 {
>> + global:
>> +
>> + rte_acl_add_rules;
>> + rte_acl_build;
>> + rte_acl_classify;
>> + rte_acl_classify_alg;
>> + rte_acl_classify_scalar;
>> + rte_acl_create;
>> + rte_acl_dump;
>> + rte_acl_find_existing;
>> + rte_acl_free;
>> + rte_acl_ipv4vlan_add_rules;
>> + rte_acl_ipv4vlan_build;
>> + rte_acl_list_dump;
>> + rte_acl_reset;
>> + rte_acl_reset_rules;
>> + rte_acl_set_ctx_classify;
>> +
>> + local: *;
>> + };
>> +
>> +This file needs to be modified as follows
>> +
>> +.. code-block:: none
>> +
>> + DPDK_2.0 {
>> + global:
>> +
>> + rte_acl_add_rules;
>> + rte_acl_build;
>> + rte_acl_classify;
>> + rte_acl_classify_alg;
>> + rte_acl_classify_scalar;
>> + rte_acl_create;
>> + rte_acl_dump;
>> + rte_acl_find_existing;
>> + rte_acl_free;
>> + rte_acl_ipv4vlan_add_rules;
>> + rte_acl_ipv4vlan_build;
>> + rte_acl_list_dump;
>> + rte_acl_reset;
>> + rte_acl_reset_rules;
>> + rte_acl_set_ctx_classify;
>> +
>> + local: *;
>> + };
>> +
>> + DPDK_2.1 {
>> + global:
>> + rte_acl_create;
>> +
>> + } DPDK_2.0;
>> +
>> +The addition of the new block tells the linker that a new version node is
>> +available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
>> +symbols from the DPDK_2.0 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
>> +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
>> +
>> +.. code-block:: c
>> +
>> + struct rte_acl_ctx *
>> + -rte_acl_create(const struct rte_acl_param *param)
>> + +rte_acl_create_v20(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. That is our next step, mapping this new
>> +symbol name to the initial symbol name at version node 2.0. Immediately after
>> +the function, we add this line of code
>> +
>> +.. code-block:: c
>> +
>> + VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> +
>> +Remembering to also add the rte_compat.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 at DPDK_2.0``, 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 2.1 version of the symbol. We create a new function
>> +name, with a different suffix, and implement it appropriately
>> +
>> +.. code-block:: c
>> +
>> + struct rte_acl_ctx *
>> + rte_acl_create_v21(const struct rte_acl_param *param, int debug);
>> + {
>> + struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
>> +
>> + ctx->debug = debug;
>> +
>> + return ctx;
>> + }
>> +
>> +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 at DPDK_2.1``. 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
>> +
>> +.. code-block:: c
>> +
>> + struct rte_acl_ctx *
>> + -rte_acl_create(const struct rte_acl_param *param);
>> + +rte_acl_create(const struct rte_acl_param *param, int debug);
>> + +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> +
>> +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_2.1
>> +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.
>> +
>> +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
>> +defined, we add this
>> +
>> +.. code-block:: c
>> +
>> + struct rte_acl_ctx *
>> + rte_acl_create_v21(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);
>> +
>> +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``
>> +
>> +That's it, on the next shared library rebuild, there will be two versions of
>> +rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
>> +and a new DPDK_2.1 version, used by future built applications.
>> +
>> +
>> +Deprecating part of a public API
>> +________________________________
>> +
>> +Lets assume that you've done the above update, and after a few releases have
>> +passed 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 file:
>> +
>> +.. code-block:: none
>> +
>> + DPDK_2.0 {
>> + global:
>> +
>> + rte_acl_add_rules;
>> + rte_acl_build;
>> + rte_acl_classify;
>> + rte_acl_classify_alg;
>> + rte_acl_classify_scalar;
>> + rte_acl_dump;
>> + - rte_acl_create
>> + rte_acl_find_existing;
>> + rte_acl_free;
>> + rte_acl_ipv4vlan_add_rules;
>> + rte_acl_ipv4vlan_build;
>> + rte_acl_list_dump;
>> + rte_acl_reset;
>> + rte_acl_reset_rules;
>> + rte_acl_set_ctx_classify;
>> +
>> + local: *;
>> + };
>> +
>> + DPDK_2.1 {
>> + global:
>> + rte_acl_create;
>> + } DPDK_2.0;
>> +
>> +
>> +Next remove the corresponding versioned export.
>> +
>> +.. code-block:: c
>> +
>> + -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> +
>> +
>> +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. This is a
>> +coding style choice.
>> +
>> +Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
>> +indicate to applications doing dynamic linking that this is a later, and
>> +possibly incompatible library version:
>> +
>> +.. code-block:: c
>> +
>> + -LIBABIVER := 1
>> + +LIBABIVER := 2
>> +
>> +Deprecating an entire ABI version
>> +_________________________________
>> +
>> +While removing a symbol from and ABI may be useful, it is often more practical
>> +to remove an entire version node at once. If a version node completely
>> +specifies an API, then removing part of it, typically makes it incomplete. In
>> +those cases it is better to remove the entire node
>> +
>> +To do this, start by modifying the version map file, such that all symbols from
>> +the node to be removed are merged into the next node in the map
>> +
>> +In the case of our map above, it would transform to look as follows
>> +
>> +.. code-block:: none
>> +
>> + DPDK_2.1 {
>> + global:
>> +
>> + rte_acl_add_rules;
>> + rte_acl_build;
>> + rte_acl_classify;
>> + rte_acl_classify_alg;
>> + rte_acl_classify_scalar;
>> + rte_acl_dump;
>> + rte_acl_create
>> + rte_acl_find_existing;
>> + rte_acl_free;
>> + rte_acl_ipv4vlan_add_rules;
>> + rte_acl_ipv4vlan_build;
>> + rte_acl_list_dump;
>> + rte_acl_reset;
>> + rte_acl_reset_rules;
>> + rte_acl_set_ctx_classify;
>> +
>> + local: *;
>> + };
>> +
>> +Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
>> +updated to point to the new version node in any header files for all affected
>> +symbols.
>> +
>> +.. code-block:: c
>> +
>> + -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
>> + +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> +
>> +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.
>> +
>> +
>> +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 between two tags:
>> + ./devtools/validate-abi.sh v2.0.0 v2.1.0
>> +
>> + # Check between git master and local topic-branch "vhost-hacking":
>> + ./devtools/validate-abi.sh master vhost-hacking
>> +
>> +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::
>> +
>> + grep -lr Incompatible abi-check/compat_reports/
>> diff --git a/doc/guides/contributing/index.rst b/doc/guides/contributing/index.rst
>> index e2608d3..2fefd91 100644
>> --- a/doc/guides/contributing/index.rst
>> +++ b/doc/guides/contributing/index.rst
>> @@ -10,7 +10,8 @@ Contributor's Guidelines
>>
>> coding_style
>> design
>> - versioning
>> + abi_policy
>> + abi_versioning
>> documentation
>> patches
>> vulnerability
>> diff --git a/doc/guides/contributing/versioning.rst b/doc/guides/contributing/versioning.rst
>> deleted file mode 100644
>> index 3ab2c43..0000000
>> --- a/doc/guides/contributing/versioning.rst
>> +++ /dev/null
>> @@ -1,591 +0,0 @@
>> -.. SPDX-License-Identifier: BSD-3-Clause
>> - Copyright 2018 The DPDK contributors
>> -
>> -DPDK ABI/API policy
>> -===================
>> -
>> -Description
>> ------------
>> -
>> -This document details some methods for handling ABI management in the DPDK.
>> -
>> -General Guidelines
>> -------------------
>> -
>> -#. Whenever possible, ABI should be preserved
>> -#. ABI/API may be changed with a deprecation process
>> -#. The modification of symbols can generally be managed with versioning
>> -#. Libraries or APIs marked in ``experimental`` state may change without constraint
>> -#. New APIs will be marked as ``experimental`` for at least one release to allow
>> - any issues found by users of the new API to be fixed quickly
>> -#. The addition of symbols is generally not problematic
>> -#. The removal of symbols generally is an ABI break and requires bumping of the
>> - LIBABIVER macro
>> -#. Updates to the minimum hardware requirements, which drop support for hardware which
>> - was previously supported, should be treated as an ABI change.
>> -
>> -What is an ABI
>> -~~~~~~~~~~~~~~
>> -
>> -An ABI (Application Binary Interface) is the set of runtime interfaces exposed
>> -by a library. It is similar to an API (Application Programming Interface) but
>> -is the result of compilation. It is also effectively cloned when applications
>> -link to dynamic libraries. That is to say when an application is compiled to
>> -link against dynamic libraries, it is assumed that the ABI remains constant
>> -between the time the application is compiled/linked, and the time that it runs.
>> -Therefore, in the case of dynamic linking, it is critical that an ABI is
>> -preserved, or (when modified), done in such a way that the application is unable
>> -to behave improperly or in an unexpected fashion.
>> -
>> -
>> -ABI/API Deprecation
>> --------------------
>> -
>> -The DPDK ABI policy
>> -~~~~~~~~~~~~~~~~~~~
>> -
>> -ABI versions are set at the time of major release labeling, and the ABI may
>> -change multiple times, without warning, between the last release label and the
>> -HEAD label of the git tree.
>> -
>> -ABI versions, once released, are available until such time as their
>> -deprecation has been noted in the Release Notes for at least one major release
>> -cycle. For example consider the case where the ABI for DPDK 2.0 has been
>> -shipped and then a decision is made to modify it during the development of
>> -DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
>> -release and the modification will be made available in the DPDK 2.2 release.
>> -
>> -ABI versions may be deprecated in whole or in part as needed by a given
>> -update.
>> -
>> -Some ABI changes may be too significant to reasonably maintain multiple
>> -versions. In those cases ABI's may be updated without backward compatibility
>> -being provided. The requirements for doing so are:
>> -
>> -#. At least 3 acknowledgments of the need to do so must be made on the
>> - dpdk.org mailing list.
>> -
>> - - The acknowledgment of the maintainer of the component is mandatory, or if
>> - no maintainer is available for the component, the tree/sub-tree maintainer
>> - for that component must acknowledge the ABI change instead.
>> -
>> - - It is also recommended that acknowledgments from different "areas of
>> - interest" be sought for each deprecation, for example: from NIC vendors,
>> - CPU vendors, end-users, etc.
>> -
>> -#. The changes (including an alternative map file) can be included with
>> - deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
>> - to provide more details about oncoming changes.
>> - ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
>> - More preferred way to provide this information is sending the feature
>> - as a separate patch and reference it in deprecation notice.
>> -
>> -#. A full deprecation cycle, as explained above, must be made to offer
>> - downstream consumers sufficient warning of the change.
>> -
>> -Note that the above process for ABI deprecation should not be undertaken
>> -lightly. ABI stability is extremely important for downstream consumers of the
>> -DPDK, especially when distributed in shared object form. Every effort should
>> -be made to preserve the ABI whenever possible. The ABI should only be changed
>> -for significant reasons, such as performance enhancements. ABI breakage due to
>> -changes such as reorganizing public structure fields for aesthetic or
>> -readability purposes should be avoided.
>> -
>> -.. note::
>> -
>> - Updates to the minimum hardware requirements, which drop support for hardware
>> - which was previously supported, should be treated as an ABI change, and
>> - follow the relevant deprecation policy procedures as above: 3 acks and
>> - announcement at least one release in advance.
>> -
>> -Examples of Deprecation Notices
>> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> -
>> -The following are some examples of ABI deprecation notices which would be
>> -added to the Release Notes:
>> -
>> -* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
>> - to be replaced with the inline function ``rte_foo()``.
>> -
>> -* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
>> - in version 2.0. Backwards compatibility will be maintained for this function
>> - until the release of version 2.1
>> -
>> -* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
>> - performance reasons. Existing binary applications will have backwards
>> - compatibility in release 2.0, while newly built binaries will need to
>> - reference the new structure variant ``struct rte_foo2``. Compatibility will
>> - be removed in release 2.2, and all applications will require updating and
>> - rebuilding to the new structure at that time, which will be renamed to the
>> - original ``struct rte_foo``.
>> -
>> -* Significant ABI changes are planned for the ``librte_dostuff`` library. The
>> - upcoming release 2.0 will not contain these changes, but release 2.1 will,
>> - and no backwards compatibility is planned due to the extensive nature of
>> - these changes. Binaries using this library built prior to version 2.1 will
>> - require updating and recompilation.
>> -
>> -New API replacing previous one
>> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> -
>> -If a new API proposed functionally replaces an existing one, when the new API
>> -becomes non-experimental then the old one is marked with ``__rte_deprecated``.
>> -Deprecated APIs are removed completely just after the next LTS.
>> -
>> -Reminder that old API should follow deprecation process to be removed.
>> -
>> -
>> -Experimental APIs
>> ------------------
>> -
>> -APIs marked as ``experimental`` are not considered part of the ABI and may
>> -change without warning at any time. Since changes to APIs are most likely
>> -immediately after their introduction, as users begin to take advantage of
>> -those new APIs and start finding issues with them, new DPDK APIs will be
>> -automatically marked as ``experimental`` to allow for a period of stabilization
>> -before they become part of a tracked ABI.
>> -
>> -Note that marking an API as experimental is a multi step process.
>> -To mark an API as experimental, the symbols which are desired to be exported
>> -must be placed in an EXPERIMENTAL version block in the corresponding libraries'
>> -version map script.
>> -Secondly, the corresponding prototypes of those exported functions (in the
>> -development header files), must be marked with the ``__rte_experimental`` tag
>> -(see ``rte_compat.h``).
>> -The DPDK build makefiles perform a check to ensure that the map file and the
>> -C code reflect the same list of symbols.
>> -This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
>> -during compilation in the corresponding library Makefile.
>> -
>> -In addition to tagging the code with ``__rte_experimental``,
>> -the doxygen markup must also contain the EXPERIMENTAL string,
>> -and the MAINTAINERS file should note the EXPERIMENTAL libraries.
>> -
>> -For removing the experimental tag associated with an API, deprecation notice
>> -is not required. Though, an API should remain in experimental state for at least
>> -one release. Thereafter, normal process of posting patch for review to mailing
>> -list can be followed.
>> -
>> -
>> -Library versioning
>> -------------------
>> -
>> -Downstreams might want to provide different DPDK releases at the same time to
>> -support multiple consumers of DPDK linked against older and newer sonames.
>> -
>> -Also due to the interdependencies that DPDK libraries can have applications
>> -might end up with an executable space in which multiple versions of a library
>> -are mapped by ld.so.
>> -
>> -Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
>> -depending on LibA.
>> -
>> -.. note::
>> -
>> - Application
>> - \-> LibA.old
>> - \-> LibB.new -> LibA.new
>> -
>> -That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
>> -If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
>> -library - versions defined in the libraries ``LIBABIVER``.
>> -An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
>> -``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
>> -
>> -
>> -ABI versioning
>> ---------------
>> -
>> -Versioning Macros
>> -~~~~~~~~~~~~~~~~~
>> -
>> -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 and
>> -arguments. Occasionally that function may need to change to accommodate new
>> -functionality or behavior. When that occurs, it is desirable to allow for
>> -backward compatibility for a time with older binaries that are dynamically
>> -linked to the DPDK.
>> -
>> -To support backward compatibility the ``rte_compat.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
>> -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.
>> -
>> -The macros exported are:
>> -
>> -* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
>> - versioned symbol ``b at DPDK_n`` to the internal function ``b_e``.
>> -
>> -* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
>> - the linker to bind references to symbol ``b`` to the internal symbol
>> - ``b_e``.
>> -
>> -* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
>> - fully qualified function ``p``, so that if a symbol becomes versioned, it
>> - can still be mapped back to the public symbol name.
>> -
>> -Examples of ABI Macro use
>> -^^^^^^^^^^^^^^^^^^^^^^^^^
>> -
>> -Updating a public API
>> -_____________________
>> -
>> -Assume we have a function as follows
>> -
>> -.. 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)
>> - {
>> - ...
>> - }
>> -
>> -
>> -Assume that struct rte_acl_ctx is a private structure, and that a developer
>> -wishes to enhance the acl api so that a debugging flag can be enabled on a
>> -per-context basis. This requires an addition to the structure (which, being
>> -private, is safe), but it also requires modifying the code as follows
>> -
>> -.. 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, int debug)
>> - {
>> - ...
>> - }
>> -
>> -
>> -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
>> -
>> -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
>> -compatibility macros in DPDK allow a developer to use symbol versioning so that
>> -multiple functions can be mapped to the same public symbol based on when an
>> -application was linked to it. To see how this is done, we start with the
>> -requisite libraries version map file. Initially the version map file for the
>> -acl library looks like this
>> -
>> -.. code-block:: none
>> -
>> - DPDK_2.0 {
>> - global:
>> -
>> - rte_acl_add_rules;
>> - rte_acl_build;
>> - rte_acl_classify;
>> - rte_acl_classify_alg;
>> - rte_acl_classify_scalar;
>> - rte_acl_create;
>> - rte_acl_dump;
>> - rte_acl_find_existing;
>> - rte_acl_free;
>> - rte_acl_ipv4vlan_add_rules;
>> - rte_acl_ipv4vlan_build;
>> - rte_acl_list_dump;
>> - rte_acl_reset;
>> - rte_acl_reset_rules;
>> - rte_acl_set_ctx_classify;
>> -
>> - local: *;
>> - };
>> -
>> -This file needs to be modified as follows
>> -
>> -.. code-block:: none
>> -
>> - DPDK_2.0 {
>> - global:
>> -
>> - rte_acl_add_rules;
>> - rte_acl_build;
>> - rte_acl_classify;
>> - rte_acl_classify_alg;
>> - rte_acl_classify_scalar;
>> - rte_acl_create;
>> - rte_acl_dump;
>> - rte_acl_find_existing;
>> - rte_acl_free;
>> - rte_acl_ipv4vlan_add_rules;
>> - rte_acl_ipv4vlan_build;
>> - rte_acl_list_dump;
>> - rte_acl_reset;
>> - rte_acl_reset_rules;
>> - rte_acl_set_ctx_classify;
>> -
>> - local: *;
>> - };
>> -
>> - DPDK_2.1 {
>> - global:
>> - rte_acl_create;
>> -
>> - } DPDK_2.0;
>> -
>> -The addition of the new block tells the linker that a new version node is
>> -available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
>> -symbols from the DPDK_2.0 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
>> -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
>> -
>> -.. code-block:: c
>> -
>> - struct rte_acl_ctx *
>> - -rte_acl_create(const struct rte_acl_param *param)
>> - +rte_acl_create_v20(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. That is our next step, mapping this new
>> -symbol name to the initial symbol name at version node 2.0. Immediately after
>> -the function, we add this line of code
>> -
>> -.. code-block:: c
>> -
>> - VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> -
>> -Remembering to also add the rte_compat.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 at DPDK_2.0``, 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 2.1 version of the symbol. We create a new function
>> -name, with a different suffix, and implement it appropriately
>> -
>> -.. code-block:: c
>> -
>> - struct rte_acl_ctx *
>> - rte_acl_create_v21(const struct rte_acl_param *param, int debug);
>> - {
>> - struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
>> -
>> - ctx->debug = debug;
>> -
>> - return ctx;
>> - }
>> -
>> -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 at DPDK_2.1``. 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
>> -
>> -.. code-block:: c
>> -
>> - struct rte_acl_ctx *
>> - -rte_acl_create(const struct rte_acl_param *param);
>> - +rte_acl_create(const struct rte_acl_param *param, int debug);
>> - +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> -
>> -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_2.1
>> -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.
>> -
>> -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
>> -defined, we add this
>> -
>> -.. code-block:: c
>> -
>> - struct rte_acl_ctx *
>> - rte_acl_create_v21(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);
>> -
>> -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``
>> -
>> -That's it, on the next shared library rebuild, there will be two versions of
>> -rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
>> -and a new DPDK_2.1 version, used by future built applications.
>> -
>> -
>> -Deprecating part of a public API
>> -________________________________
>> -
>> -Lets assume that you've done the above update, and after a few releases have
>> -passed 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 file:
>> -
>> -.. code-block:: none
>> -
>> - DPDK_2.0 {
>> - global:
>> -
>> - rte_acl_add_rules;
>> - rte_acl_build;
>> - rte_acl_classify;
>> - rte_acl_classify_alg;
>> - rte_acl_classify_scalar;
>> - rte_acl_dump;
>> - - rte_acl_create
>> - rte_acl_find_existing;
>> - rte_acl_free;
>> - rte_acl_ipv4vlan_add_rules;
>> - rte_acl_ipv4vlan_build;
>> - rte_acl_list_dump;
>> - rte_acl_reset;
>> - rte_acl_reset_rules;
>> - rte_acl_set_ctx_classify;
>> -
>> - local: *;
>> - };
>> -
>> - DPDK_2.1 {
>> - global:
>> - rte_acl_create;
>> - } DPDK_2.0;
>> -
>> -
>> -Next remove the corresponding versioned export.
>> -
>> -.. code-block:: c
>> -
>> - -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> -
>> -
>> -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. This is a
>> -coding style choice.
>> -
>> -Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
>> -indicate to applications doing dynamic linking that this is a later, and
>> -possibly incompatible library version:
>> -
>> -.. code-block:: c
>> -
>> - -LIBABIVER := 1
>> - +LIBABIVER := 2
>> -
>> -Deprecating an entire ABI version
>> -_________________________________
>> -
>> -While removing a symbol from and ABI may be useful, it is often more practical
>> -to remove an entire version node at once. If a version node completely
>> -specifies an API, then removing part of it, typically makes it incomplete. In
>> -those cases it is better to remove the entire node
>> -
>> -To do this, start by modifying the version map file, such that all symbols from
>> -the node to be removed are merged into the next node in the map
>> -
>> -In the case of our map above, it would transform to look as follows
>> -
>> -.. code-block:: none
>> -
>> - DPDK_2.1 {
>> - global:
>> -
>> - rte_acl_add_rules;
>> - rte_acl_build;
>> - rte_acl_classify;
>> - rte_acl_classify_alg;
>> - rte_acl_classify_scalar;
>> - rte_acl_dump;
>> - rte_acl_create
>> - rte_acl_find_existing;
>> - rte_acl_free;
>> - rte_acl_ipv4vlan_add_rules;
>> - rte_acl_ipv4vlan_build;
>> - rte_acl_list_dump;
>> - rte_acl_reset;
>> - rte_acl_reset_rules;
>> - rte_acl_set_ctx_classify;
>> -
>> - local: *;
>> - };
>> -
>> -Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
>> -updated to point to the new version node in any header files for all affected
>> -symbols.
>> -
>> -.. code-block:: c
>> -
>> - -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
>> - +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> -
>> -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.
>> -
>> -
>> -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 between two tags:
>> - ./devtools/validate-abi.sh v2.0.0 v2.1.0
>> -
>> - # Check between git master and local topic-branch "vhost-hacking":
>> - ./devtools/validate-abi.sh master vhost-hacking
>> -
>> -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::
>> -
>> - grep -lr Incompatible abi-check/compat_reports/
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