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[[migrating-from-ol-versions]]
== Migrating from older Buildroot versions

Some versions have introduced backward incompatibilities. This section
explains those incompatibilities, and for each explains what to do to
complete the migration.

[[migrating-approach]]
=== General approach

To migrate from an older Buildroot version, take the following steps.

. For all your configurations, do a build in the old Buildroot
  environment. Run +make graph-size+. Save
  +graphs/file-size-stats.csv+ in a different location. Run +make
  clean+ to remove the rest.
. Review the specific migration notes below and make the required
  adaptations to external packages and custom build scripts.
. Update Buildroot.
. Run +make menuconfig+ starting from the existing +.config+.
. If anything is enabled in the Legacy menu, check its help text,
  unselect it, and save the configuration.
. For more details, review the git commit messages for the packages that
  you need. Change into the +packages+ directory and run
  +git log <old version>.. -- <your packages>+.
. Build in the new Buildroot environment.
. Fix build issues in external packages (usually due to updated
  dependencies).
. Run +make graph-size+.
. Compare the new +file-size-stats.csv+ with the original one, to
  check if no required files have disappeared and if no new big unneeded
  files have appeared.
. For configuration (and other) files in a custom overlay that overwrite
  files created by Buildroot, check if there are changes in the
  Buildroot-generated file that need to be propagated to your custom
  file.

[[br2-external-converting]]
=== Migrating to 2016.11

Before Buildroot 2016.11, it was possible to use only one br2-external
tree at once. With Buildroot 2016.11 came the possibility to use more
than one simultaneously (for details, see xref:outside-br-custom[]).

This however means that older br2-external trees are not usable as-is.
A minor change has to be made: adding a name to your br2-external tree.

This can be done very easily in just a few steps:

 * First, create a new file named +external.desc+, at the root of your
   br2-external tree, with a single line defining the name of your
   br2-external tree:
+
----
$ echo 'name: NAME_OF_YOUR_TREE' >external.desc
----
+
.Note
Be careful when choosing a name: It has to be unique and be made
with only ASCII characters from the set +[A-Za-z0-9_]+.

 * Then, change every occurrence of +BR2_EXTERNAL+ in your br2-external
   tree with the new variable:
+
----
$ find . -type f | xargs sed -i 's/BR2_EXTERNAL/BR2_EXTERNAL_NAME_OF_YOUR_TREE_PATH/g'
----

Now, your br2-external tree can be used with Buildroot 2016.11 onward.

.Note:
This change makes your br2-external tree incompatible with Buildroot
before 2016.11.

[[migrating-host-usr]]
=== Migrating to 2017.08

Before Buildroot 2017.08, host packages were installed in +$(HOST_DIR)/usr+
(with e.g. the autotools' +--prefix=$(HOST_DIR)/usr+). With Buildroot
2017.08, they are now installed directly in +$(HOST_DIR)+.

Whenever a package installs an executable that is linked with a library
in +$(HOST_DIR)/lib+, it must have an RPATH pointing to that directory.

An RPATH pointing to +$(HOST_DIR)/usr/lib+ is no longer accepted.

[[migrating-svn-externals]]
=== Migrating to 2023.11

Before Buildroot 2023.11, the subversion download backend unconditionally
retrieved the external references (objects with an `svn:externals`
property). Starting with 2023.11, externals are no longer retrieved by
default; if you need them, set +LIBFOO_SVN_EXTERNALS+ to +YES+. This
change implies that:

* the generated archive content may change, and thus the hashes may need
  to be updated appropriately;
* the archive version suffix has been updated to +-br3+, so the hash
  files must be updated appropriately.

Before Buildroot 2023.11, it was possible (but undocumented and unused)
to apply architecture-specific patches, by prefixing the patch filename
with the architecture, e.g. `0001-some-changes.patch.arm` and such a
patch would only be applied for that architecture. With Buildroot 2023.11,
this is no longer supported, and such patches are no longer applied at
all.

If you still need per-architecture patches, then you may provide a
xref:hooks[pre-patch hook] that copies the patches applicable to the
configured architecture, e.g.:

----
define LIBFOO_ARCH_PATCHES
    $(foreach p,$(wildcard $(LIBFOO_PKGDIR)/*.patch.$(ARCH)), \
        cp -f $(p) $(patsubst %.$(ARCH),%,$(p))
    )
endef
LIBFOO_PRE_PATCH_HOOKS += LIBFOO_ARCH_PATCHES
----

Note that no package in Buildroot has architecture-specific patches, and
that such patches will most probably not be accepted.
