[Buildroot] [RFCv2 0/7] Per-package SDK and target directories
Thomas Petazzoni
thomas.petazzoni at free-electrons.com
Fri Nov 24 16:46:03 UTC 2017
Hello,
Here is a second iteration of the per-package SDK and target directory
implementation. This is definitely not ready for merging, but it
already works enough to give it some exposure. I'm sending it early so
that:
- Interested people can take the patches, try them on their
configurations, and report me the problems that they face.
- Interested people start reviewing the patch series will it is still
small and simple, because I'm sure it will grow quite a bit before
it gets to a point where it can be merged.
If you're interested in testing it, you can find the patch series at:
http://git.free-electrons.com/users/thomas-petazzoni/buildroot/log/?h=ppsh-v2
Note: in the following discussion, we use the terminology "SDK" to
refer to the combination of HOST_DIR and STAGING_DIR, i.e the
cross-compiler and its sysroot with target libraries/headers, and a
bunch of other native programs. Since STAGING_DIR is included inside
HOST_DIR, the SDK directory is in essence just HOST_DIR.
Changes since v1
================
- Rebased on the latest Buildroot next branch
- The pkg-config changes are reworked according to Arnout's comments:
only @STAGING_SUBDIR@ is replaced in pkg-config.in to generate
pkg-config, the rest of the logic is internal to the script.
- New patch to move the "host skeleton" logic into a proper
host-skeleton package.
- New patch to have the CMake related files generated as part of the
toolchain package.
- New patch to add a new "install" step that depends on the different
install steps (target, staging, images, host). This is needed to
later add some logic that is executed once all install steps of a
package have been done.
- Fix the approach to solve the RPATH logic: instead of using
LD_LIBRARY_PATH, we actually fix with patchelf the RPATH of host
binaries right after their installation.
- Misc other improvements in the per-package SDK implementation.
What is per-package SDK and target?
===================================
Currently, output/host (SDK) and output/target are global directories:
all packages use files installed by other packages in those global
directories, and in turn into those global directories.
The idea of per-package SDK and target is that instead of having such
global directories, we would have one SDK directory and one target
directory per-package, containing just what this package needs
(dependencies), and in which the package installs its files.
Why do we want per-package SDK and target?
==========================================
There are two main motivations for per-package SDK and target
directories, which are related:
1. Since the SDK directory is global, a package can currently see
libraries/headers that it has not explicitly expressed a
dependency on. So package A may not have a dependency on package
B, but if package B happens to have been installed before, and
package A "configure" script automaticatically detects a library
installed by package B, it will use it. We have added tons of
conditional dependencies in Buildroot to make such situations less
problematic, but it is an endless fight, as upstream developers
constantly add more optional dependencies to their software.
Using per-package SDK, a given package uses as its SDK a directory
that only contains the libraries/headers from packages explicitly
listed in its dependencies. So it cannot mistakenly see a
library/header installed by another package.
2. Top-level parallel build (building multiple packages in parallel)
is currently not enabled because we have global SDK and target
directories.
Let's imagine package A configure script auto-detects a library
provided by package B, but Buildroot does not encode this
dependency in package A's .mk file. Package A and package B are
therefore totally independent from a build dependency point of
view.
Without top-level parallel build (current situation), you have a
guarantee on the build order: either A is always built before B,
or B is always built before A. So at least, every build gives the
same result: A is built with B's functionality or without it, but
it is consistent accross rebuilds.
If you enable top-level parallel build, because A and B are
totally independent, you can get A built before B or B built
before A depending on the build scheduling. This can change at
every build! This means that for a given configuration, A will
sometimes be built with B's functionality, sometimes not. Totally
unacceptable.
And of course, this extends to case where package B gets installed
while package A is being configured. So package A configure script
will see some parts of B being installed, other parts not
installed, causing all sort of weird and difficult to debug race
conditions.
By having per-package SDK directories, we ensure that package A
will only see the dependencies its has explicitly expressed, and
that no other package gets installed in parallel in the same SDK
directory.
How is it implemented?
======================
The basic idea is pretty simple:
- For each package, we have:
output/per-package/<package>/host, which is the specific SDK
directory for <package>.
output/per-package/<package>/target, which is the specific target
directory for <package>.
- Before <package> is configured, we copy into its specific SDK and
target directories the SDK and target directories from its direct
dependencies. This basically populates its SDK with the
cross-compiler and all libraries that <package> needs. This copy is
done using rsync with hard links, so it is very fast and cheap from
a storage consumption point of view.
- While <package> is being built, HOST_DIR, STAGING_DIR and
TARGET_DIR are tweaked to point to the current <package> specific
SDK and target directories. I.e, HOST_DIR no longer points to
output/host, but to output/per-package/<package>/host/.
And this is basically enough to get things working!
There are of course a few additional things to do:
- At the end of the build, we still want a global target directory
(to generate the filesystem images) and a global SDK. Therefore, in
target-finalize, we assemble such global directories by copying the
per-package SDK and target directories from all packages listed in
the $(PACKAGES) variable.
- We need to fix our pkg-config wrapper script so that it uses
relative path instead of absolute paths. This allows the wrapper
script to work regardless of which per-package SDK directory it is
installed in.
- We need to move away from using absolute RPATH for host binaries,
and to achieve that we fix the RPATH to $ORIGIN/../lib in host
binaries right after the installation of each package.
What remains to be done?
========================
- Completely get rid of the global HOST_DIR, TARGET_DIR and
STAGING_DIR definitions, so that nothing uses them, and they really
become per-package variables.
- While the toolchain sysroot, pkg-config paths and host RPATHs are
properly handled, there are quite certainly a lot of other places
that have absolute paths that won't work well with per-package SDK,
and that need to be adjusted.
- Perhaps use a temporary per-package SDK and target directory when
building a package, and rename it to the final name once the
package has finished building. This would allow to detect
situations where the per-package SDK directory of package A
contains absolute paths referring to the per-package SDK directory
of package B. Such absolute paths are wrong, but we currently don't
see them because the per-package SDK directory for package B still
exists.
- Think about what needs to be done about the output/images/
folder. Should it also be per-package like we do for output/target?
- Handle host-lzip, host-tar and host-ccache properly, as well as
PATCH_DEPENDENCIES.
- Many other issues that I'm sure people will report.
Comparison with Gustavo's patch series
======================================
Gustavo Zacarias did a previous implementation of this, available in
http://repo.or.cz/buildroot-gz.git/shortlog/refs/heads/pps3-next. Compared
to Gustavo's patch series, this patch series:
- Implement per-package SDK and target directories, while Gustavo was
only doing per-package staging.
- Gustavo had several patches to pass BR_TOOLCHAIN_SYSROOT to the
toolchain wrapper to pass the location of the current sysroot.
This is no longer needed, because 1/ we're doing a full per-package
SDK directory rather than per-package staging, which means the
sysroot is always at the same relative location compared to the
cross-compiler binary and 2/ the toolchain wrapper derives the
sysroot location relatively to the wrapper location. Thanks to
this, the following patches from Gustavo are (I believe) not
needed:
http://repo.or.cz/buildroot-gz.git/commitdiff/1ef6e798064649726d396bcb581ddbe4573c2460
http://repo.or.cz/buildroot-gz.git/commitdiff/d15f6c6917b555bbbbbf97c292fad4db9d4007d4
http://repo.or.cz/buildroot-gz.git/commitdiff/95900b65c29a010d85a769c9c6374cf3835f2169
http://repo.or.cz/buildroot-gz.git/commitdiff/7ed53a5437ab09b85bf6d1953f6ff6049dfcc114
- Gustavo had a patch to make our pkg-config wrapper script look at
BR_TOOLCHAIN_SYSROOT, in order to find the
/usr/{lib,share}/pkgconfig folders of the current sysroot. Just
like for the toolchain-wrapper, such a change is no longer needed,
and a simple change to our pkg-config script to use relative paths
is sufficient.
- I haven't integrated Gustavo patches that move from $(shell ...) to
using backticks to delay the evaluation of
STAGING_DIR/HOST_DIR/TARGET_DIR:
http://repo.or.cz/buildroot-gz.git/commitdiff/0c11c60865f1445830643bb404f92c20d563260c
http://repo.or.cz/buildroot-gz.git/commitdiff/207d2248ec8542293b6201b5c86f971021a3a591
http://repo.or.cz/buildroot-gz.git/commitdiff/7f6a69819fbb176e29a1c3a53b4a76efe87dad15
http://repo.or.cz/buildroot-gz.git/commitdiff/3328a9745eee555f5e5ef7df835afc26612ecd7b
http://repo.or.cz/buildroot-gz.git/commitdiff/45a9d8c2aa6f3c0d2d8ed989d843890025faa3e8
- I haven't looked at Qt specific issues, such as the ones fixed by
Gustavo in:
http://repo.or.cz/buildroot-gz.git/commitdiff/643e982e635f4386ccefcda9da4b84536af84d04
- I am not doing all the .la files, *-config, *.prl, etc. tweaks that
Gustavo is doing in:
http://repo.or.cz/buildroot-gz.git/commitdiff/3f7b227b4c8e4514df6e5d54f88fcfb3a3a4bae0
It is part of the "remaining absolute paths that need to be fixed"
item that I mentionned above.
Best regards,
Thomas
Thomas Petazzoni (7):
pkgconf: use relative path to STAGING_DIR instead of absolute path
toolchain: post-pone evaluation of TOOLCHAIN_EXTERNAL_BIN
Makefile, skeleton: move the host skeleton logic to host-skeleton
package
pkg-cmake: install CMake files as part of a package
pkg-generic: add .stamp_installed step
core: change host RPATH handling
core: implement per-package SDK and target
Makefile | 34 +++++------
package/Makefile.in | 2 +-
package/pkg-cmake.mk | 12 ++--
package/pkg-generic.mk | 71 ++++++++++++++--------
package/pkgconf/pkg-config.in | 5 +-
package/pkgconf/pkgconf.mk | 3 +-
package/skeleton/skeleton.mk | 12 ++++
support/scripts/fix-rpath | 31 ++++++----
.../toolchain-external/pkg-toolchain-external.mk | 2 +-
toolchain/toolchain/toolchain.mk | 3 -
10 files changed, 108 insertions(+), 67 deletions(-)
--
2.13.6
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