[RFC PATCH 1/9] bitbake.conf: Pad rpath and remove build ID in native binaries

[Jacob Kroon <jacob.kroon@gmail.com>]

Try to make sure that the RUNTIME dynamic entry size is the same for all
binaries produced with the native compiler. This is necessary in order to
produce identical binaries when using differently sized buildpaths. I've
tried using only patchelf, and keeping the linker flags as they are, but
I am unable to produce identical binaries. Has anyone else managed to do
this with patchelf ? If not, maybe we can write a new tool that can handle it ?

The build-id also needs to be removed since it is calculated based on
the data present at link time. This includes STAGING_LIBDIR_NATIVE
and STAGING_BASE_LIBDIR_NATIVE. Both will differ and they need to be temporarily
preserved since some recipes will execute the binaries during do_install()
(for example python3-native). Later on these are removed in chrpath.bbclass.

This hack is the first step for producing identical native binaries when using
different build paths. 'zstd-native' is a working example.

Signed-off-by: Jacob Kroon <jacob.kroon@gmail.com>
---
 meta/classes/chrpath.bbclass | 3 +++
 meta/conf/bitbake.conf       | 6 +++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/meta/classes/chrpath.bbclass b/meta/classes/chrpath.bbclass
index 26b984c4db..3c6956304a 100644
--- a/meta/classes/chrpath.bbclass
+++ b/meta/classes/chrpath.bbclass
@@ -24,6 +24,9 @@ def process_file_linux(cmd, fpath, rootdir, baseprefix, tmpdir, d, break_hardlin
     new_rpaths = []
     modified = False
     for rpath in rpaths:
+        if rpath.startswith('rpath-padding-'):
+            modified = True
+            continue
         # If rpath is already dynamic copy it to new_rpath and continue
         if rpath.find("$ORIGIN") != -1:
             new_rpaths.append(rpath)
diff --git a/meta/conf/bitbake.conf b/meta/conf/bitbake.conf
index fba99e8f0c..9621023354 100644
--- a/meta/conf/bitbake.conf
+++ b/meta/conf/bitbake.conf
@@ -580,6 +580,8 @@ BUILDSDK_CXXFLAGS = "${BUILDSDK_CFLAGS}"
 export CXXFLAGS = "${TARGET_CXXFLAGS}"
 TARGET_CXXFLAGS = "${TARGET_CFLAGS}"
 
+RPATH_PADDING ?= "rpath-padding-${@'x' * (512 - len(d.expand('${STAGING_LIBDIR_NATIVE}:${STAGING_BASE_LIBDIR_NATIVE}:rpath-padding-')))}"
+RPATH_PADDING_FLAG ?= "-Wl,-rpath,${RPATH_PADDING}"
 export BUILD_LDFLAGS = "-L${STAGING_LIBDIR_NATIVE} \
                         -L${STAGING_BASE_LIBDIR_NATIVE} \
                         -Wl,--enable-new-dtags \
@@ -587,7 +589,9 @@ export BUILD_LDFLAGS = "-L${STAGING_LIBDIR_NATIVE} \
                         -Wl,-rpath-link,${STAGING_BASE_LIBDIR_NATIVE} \
                         -Wl,-rpath,${STAGING_LIBDIR_NATIVE} \
                         -Wl,-rpath,${STAGING_BASE_LIBDIR_NATIVE} \
-                        -Wl,-O1"
+                        ${RPATH_PADDING_FLAG} \
+                        -Wl,-O1 \
+                        -Wl,--build-id=none"
 
 BUILDSDK_LDFLAGS = "-Wl,-O1"