On 8/5/21 6:21 AM, Richard Purdie wrote:

On Wed, 2021-08-04 at 20:13 -0400, Randy MacLeod wrote:

quoted

On 2021-07-27 9:34 a.m., Tony Battersby wrote:

quoted

Currently, enabling Link Time Optimization via:

require conf/distro/include/lto.inc
DISTRO_FEATURES_append = " lto"

makes the build non-reproducible (as in
https://reproducible-builds.org/).  This patch set fixes some of the
problems, but is not yet a complete solution.

This patch set addresses the following bugs:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=14481
https://bugzilla.yoctoproject.org/show_bug.cgi?id=14490

openembedded-core patches
1/4: lto.inc: disable LTO for grub
2/4: gcc: Backport patch to make LTO builds more reproducible
3/4: bitbake.conf: add DEBUG_PREFIX_MAP to TARGET_LDFLAGS

openembedded-devel patches
4/4: net-snmp: fix QA Issue after LDFLAGS change

Patch 3 adds DEBUG_PREFIX_MAP to TARGET_LDFLAGS (it was already in
TARGET_CFLAGS).  This could possibly be done differently, such as by
removing it from TARGET_CFLAGS and adding it to TOOLCHAIN_OPTIONS,
TARGET_CC_ARCH, or TUNE_CCARGS, but I haven't tested those.  Let me know
if there is a better/preferred way to do it.

The TARGET_LDFLAGS change broke net-snmp from meta-networking, so I have
included a patch to fix that.  Other packages might have been broken as
well, although I haven't found any others.

With all these patches, there are still many shared libraries in /lib
and /usr/lib that are still not reproducible with LTO enabled because
x86_64-poky-linux-libtool filters out the -f*-prefix-map flags added by
patch 3 when linking shared libraries.  /usr/lib/libbz2.so.1.0.6 from
the libbz2 package from the bzip2 recipe is a good example.  I do not
have a patch for that problem.  I will leave that to someone else.

So this is what we need to achieve reproducible LTO builds:
*) This patch set
*) A fix for libtool
*) Add LTO to reproducible builds testing if appropriate (e.g.
meta/lib/oeqa/selftest/cases/reproducible.py, CI on Autobuilder)
*) Fixes for individual packages, if needed
*) Once everything works, update the documentation again (I previously
requested a documentation change for this bug, which will eventually
show up at
http://docs.yoctoproject.org/test-manual/reproducible-builds.html).

This is certainly a few steps in the right direction with a good outline
of what's next.

I suspect that Richard has been busy with other things like overrides
and the update to glibc-2.34.

Do you have any suggestions or questions about what we should do
with this patch series Richard?

Thanks for the reminder, I've been meaning to queue/test this which I will
do. The gcc version has been bumped but I ported the patch forward to it
and the patches are in master-next for testing. It is great to see this
support moving forward.

Much as it pains me to admit having any libtool knowledge, I may be able to
help with that bit. There is an untested patch below which may address that
issue, or at least give a good hint on how to do it if it doesn't work. I
don't have an environment to test easily right now.

Cheers,

Richard

I tested your libtool patch in master-next with the bzip2 recipe.  It
works as intended; libbz2.so.1.0.6 and all the other output files are
now reproducible with LTO enabled.  I also verified that libtool is
passing the -f*-prefix-map flags to the link command in log.do_compile
as intended.

I also verified that core-image-minimal builds successfully with the
libtool patch.

Tony Battersby