[PATCH v3 0/1] lib/oe/package: Add strip keep-section support

[PATCH v3 0/1] lib/oe/package: Add strip keep-section support

[Mathieu Othacehe]

Hello,

This is v3 of the .debug_frame / keep-section patch, picking back up the
thread from last year:

  v1 (PACKAGE_KEEP_DEBUG_FRAME):
  https://lists.openembedded.org/g/openembedded-core/message/203797

  v2 (PACKAGE_KEEP_SECTIONS):
  https://patchwork.yoctoproject.org/project/oe-core/patch/20250204103744.27883-1-othacehe@gnu.org/

Quick recap of the motivation: on 32-bit Arm, GCC's default EHABI unwind
tables (.ARM.exidx / .ARM.extab) don't currently allow libunwind to
produce a full backtrace once execution reaches the C++ termination path
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117941). GCC also emits
DWARF Call Frame Information for the same functions under .debug_frame,
which does allow a complete backtrace, but that section is unconditionally
stripped today. This series lets a recipe opt back in on a per-section
basis via PACKAGE_KEEP_SECTIONS, e.g.:

  PACKAGE_KEEP_SECTIONS:pn-myrecipe = ".debug_frame"

What's new in v3:

- Rebased on master, in particular on top of the runstrip() argument
  cleanup that landed since v2 -- no more tuple unpacking

- Added an oe-selftest case (package.PackageKeepSections) that builds
  core-image-minimal for qemuarm and uses readelf to show busybox loses
  .debug_frame by default and keeps it once PACKAGE_KEEP_SECTIONS is set,
  per Alexander's request for test coverage on v2.

- A couple of open points from the v2 thread I'd like to address before
  this goes further:

  * Richard asked whether this should just be folded into minidebuginfo
    instead of being a separate "magic" option. minidebuginfo only
    injects compressed *symbol* information (.gnu_debugdata); it says
    nothing about unwind data. PACKAGE_KEEP_SECTIONS is orthogonal --
    you need both symbols and unwind information to get a readable
    on-target backtrace, but a user may reasonably want only one of the
    two (e.g. GDB against a remote symbol store vs. a fully standalone
    coredump). I'd rather keep this as a separate, generic, opt-in knob
    than silently grow every minidebuginfo image by ~70KB per Arm binary
    that uses C++ exceptions.

  * Khem asked whether minidebuginfo could reuse .ARM.exidx/.ARM.extab
    the way it uses .eh_frame elsewhere. Per the GCC bug above, those
    EHABI tables are exactly the ones that currently produce partial
    backtraces on Arm -- that limitation is the reason this series exists.
    If that gets fixed on the GCC side, PACKAGE_KEEP_SECTIONS simply
    becomes unnecessary for this particular use case, but until then
    .debug_frame is the only way to get complete backtraces on 32-bit Arm.

- The matching ref-manual documentation for PACKAGE_KEEP_SECTIONS has been
  sent as a separate patch to the docs list.

Mathieu Othacehe (1):
  lib/oe/package: Add strip keep-section support

 meta/classes-global/staging.bbclass     |  4 +-
 meta/lib/oe/package.py                  | 19 +++++++--
 meta/lib/oeqa/selftest/cases/package.py | 52 ++++++++++++++++++++++++-
 3 files changed, 69 insertions(+), 6 deletions(-)

-- 
2.34.1

[PATCH 1/1] lib/oe/package: Add strip keep-section support

[Mathieu Othacehe]

On 32-bit Arm, the .ARM.extab and .ARM.exidx unwinding sections do not
always provide enough information to get a full backtrace on C++
exceptions:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117941

In addition to those unwinding sections, GCC also emits unwinding
instructions in DWARF format under the .debug_frame section. By
instructing 'strip' not to remove that section, libunwind can use it
to produce a full backtrace, for example when an unhandled C++
exception is thrown.

Add a PACKAGE_KEEP_SECTIONS variable, listing space separated ELF
section names that should be kept around instead of stripped, for
example:

  PACKAGE_KEEP_SECTIONS:pn-myrecipe = ".debug_frame"

This variable is never applied to kernel modules, which are covered
by CONFIG_UNWINDER_* instead.

Add a oe-selftest case building core-image-minimal for qemuarm, and
checking with readelf that busybox loses its .debug_frame section by
default, but keeps it once PACKAGE_KEEP_SECTIONS is set.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>
---
 meta/classes-global/staging.bbclass     |  4 +-
 meta/lib/oe/package.py                  | 19 +++++++--
 meta/lib/oeqa/selftest/cases/package.py | 52 ++++++++++++++++++++++++-
 3 files changed, 69 insertions(+), 6 deletions(-)

diff --git a/meta/classes-global/staging.bbclass b/meta/classes-global/staging.bbclass
index 5833abebc8..9ea4c644db 100644
--- a/meta/classes-global/staging.bbclass
+++ b/meta/classes-global/staging.bbclass
@@ -91,10 +91,12 @@ python sysroot_strip () {
     base_libdir = d.getVar("base_libdir")
     qa_already_stripped = 'already-stripped' in (d.getVar('INSANE_SKIP:' + pn) or "").split()
     strip_cmd = d.getVar("STRIP")
+    keep_sections = d.getVar('PACKAGE_KEEP_SECTIONS') or ""
 
     max_process = oe.utils.get_bb_number_threads(d)
     oe.package.strip_execs(pn, dstdir, strip_cmd, libdir, base_libdir, max_process,
-                           qa_already_stripped=qa_already_stripped)
+                           qa_already_stripped=qa_already_stripped,
+                           keep_sections=keep_sections)
 }
 
 do_populate_sysroot[dirs] = "${SYSROOT_DESTDIR}"
diff --git a/meta/lib/oe/package.py b/meta/lib/oe/package.py
index b7030643d2..620f9fefc8 100644
--- a/meta/lib/oe/package.py
+++ b/meta/lib/oe/package.py
@@ -19,7 +19,7 @@ import shutil
 import bb.parse
 import oe.cachedpath
 
-def runstrip(file, elftype, strip, extra_strip_sections=''):
+def runstrip(file, elftype, strip, extra_strip_sections='', keep_sections=''):
     # Function to strip a single file, called from split_and_strip_files below
     # A working 'file' (one which works on the target architecture)
     #
@@ -49,6 +49,10 @@ def runstrip(file, elftype, strip, extra_strip_sections=''):
             for section in extra_strip_sections.split():
                 stripcmd.extend(["--remove-section=" + section])
 
+    if keep_sections != '' and not elftype & 16:
+        for section in keep_sections.split():
+            stripcmd.extend(["--keep-section=" + section])
+
     stripcmd.append(file)
     bb.debug(1, "runstrip: %s" % stripcmd)
 
@@ -96,7 +100,8 @@ def is_static_lib(path):
             return start == magic
     return False
 
-def strip_execs(pn, dstdir, strip_cmd, libdir, base_libdir, max_process, qa_already_stripped=False):
+def strip_execs(pn, dstdir, strip_cmd, libdir, base_libdir, max_process,
+                qa_already_stripped=False, keep_sections=''):
     """
     Strip executable code (like executables, shared libraries) _in_place_
     - Based on sysroot_strip in staging.bbclass
@@ -107,6 +112,9 @@ def strip_execs(pn, dstdir, strip_cmd, libdir, base_libdir, max_process, qa_alre
     :param max_process: number of stripping processes started in parallel
     :param qa_already_stripped: Set to True if already-stripped' in ${INSANE_SKIP}
     This is for proper logging and messages only.
+    :param keep_sections: Space separated list of ELF sections to keep even
+    though the file is being stripped, for example ".debug_frame" so that
+    libunwind can use it to generate backtraces.
     """
     import stat, errno, oe.path, oe.utils
 
@@ -175,7 +183,8 @@ def strip_execs(pn, dstdir, strip_cmd, libdir, base_libdir, max_process, qa_alre
         elf_file = int(elffiles[file])
         sfiles.append((file, elf_file, strip_cmd))
 
-    oe.utils.multiprocess_launch_mp(runstrip, sfiles, max_process)
+    oe.utils.multiprocess_launch_mp(runstrip, sfiles, max_process,
+                                    extraargs=('', keep_sections))
 
 TRANSLATE = (
     ("@", "@at@"),
@@ -1359,7 +1368,9 @@ def process_split_and_strip_files(d):
             for f in staticlibs:
                 sfiles.append((f, 16, strip))
 
-        oe.utils.multiprocess_launch(oe.package.runstrip, sfiles, d)
+        keep_sections = d.getVar('PACKAGE_KEEP_SECTIONS') or ""
+        oe.utils.multiprocess_launch(oe.package.runstrip, sfiles, d,
+                                     extraargs=('', keep_sections))
 
     # Build "minidebuginfo" and reinject it back into the stripped binaries
     if bb.utils.contains('DISTRO_FEATURES', 'minidebuginfo', True, False, d):
diff --git a/meta/lib/oeqa/selftest/cases/package.py b/meta/lib/oeqa/selftest/cases/package.py
index 38ed7173fe..96aee21177 100644
--- a/meta/lib/oeqa/selftest/cases/package.py
+++ b/meta/lib/oeqa/selftest/cases/package.py
@@ -5,10 +5,12 @@
 #
 
 from oeqa.selftest.case import OESelftestTestCase
-from oeqa.utils.commands import bitbake, get_bb_vars, get_bb_var, runqemu
+from oeqa.utils.commands import bitbake, get_bb_vars, get_bb_var, runqemu, runCmd
 import subprocess, os
 import oe.path
 import re
+import tempfile
+import tarfile
 
 class VersionOrdering(OESelftestTestCase):
     # version1, version2, sort order
@@ -208,3 +210,51 @@ class PackageTests(OESelftestTestCase):
                           sysconfdir + "/selftest-chown/symlink",
                           sysconfdir + "/selftest-chown/fifotest/fifo"]:
                 check_ownership(qemu, "test", "test", path)
+
+class PackageKeepSections(OESelftestTestCase):
+    def test_package_keep_sections(self):
+        """
+        Verify that PACKAGE_KEEP_SECTIONS prevents 'strip' from removing the
+        listed ELF sections, and that they are removed as usual when the
+        variable isn't set.
+        """
+        # GCC only emits .debug_frame on targets that don't already rely on
+        # .eh_frame for unwinding, which in practice means 32-bit Arm: use
+        # qemuarm so the section actually exists before strip runs. Do this
+        # before querying any other variable below, as they all depend on
+        # MACHINE.
+        self.write_config("""
+MACHINE = "qemuarm"
+IMAGE_FSTYPES = "tar.bz2"
+""")
+
+        target_sys = get_bb_var("TARGET_SYS")
+        bb_vars = get_bb_vars(['DEPLOY_DIR_IMAGE', 'IMAGE_LINK_NAME', 'READELF'], 'core-image-minimal')
+        binutils = "binutils-cross-{}".format(get_bb_var("TARGET_ARCH"))
+        bitbake("{}:do_addto_recipe_sysroot".format(binutils))
+        native_sysroot = get_bb_var("RECIPE_SYSROOT_NATIVE", binutils)
+
+        def has_section(section):
+            with tempfile.TemporaryDirectory(prefix = "unpackfs-") as unpackedfs:
+                filename = os.path.join(bb_vars['DEPLOY_DIR_IMAGE'], "{}.tar.bz2".format(bb_vars['IMAGE_LINK_NAME']))
+                with tarfile.open(filename) as tar:
+                    tar.extract("./usr/bin/busybox.nosuid", path=unpackedfs)
+
+                r = runCmd([bb_vars['READELF'], "-W", "-S", os.path.join(unpackedfs, "usr", "bin", "busybox.nosuid")],
+                        native_sysroot = native_sysroot, target_sys = target_sys)
+                return section in r.output
+
+        bitbake("core-image-minimal")
+        self.assertFalse(has_section(".debug_frame"),
+                          "busybox should not carry a .debug_frame section by default")
+
+        self.write_config("""
+MACHINE = "qemuarm"
+IMAGE_FSTYPES = "tar.bz2"
+PACKAGE_KEEP_SECTIONS:pn-busybox = ".debug_frame"
+""")
+        bitbake("busybox -c package -f")
+        bitbake("core-image-minimal")
+        self.assertTrue(has_section(".debug_frame"),
+                         "busybox should carry a .debug_frame section when "
+                         "PACKAGE_KEEP_SECTIONS is set")
-- 
2.34.1

Re: [OE-core] [PATCH 1/1] lib/oe/package: Add strip keep-section support

[Mathieu Dubois-Briand]

On Sat Sep 12, 2026 at 12:01 AM CEST, Mathieu Othacehe via lists.openembedded.org wrote:
> On 32-bit Arm, the .ARM.extab and .ARM.exidx unwinding sections do not
> always provide enough information to get a full backtrace on C++
> exceptions:
>
>   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117941
>
> In addition to those unwinding sections, GCC also emits unwinding
> instructions in DWARF format under the .debug_frame section. By
> instructing 'strip' not to remove that section, libunwind can use it
> to produce a full backtrace, for example when an unhandled C++
> exception is thrown.
>
> Add a PACKAGE_KEEP_SECTIONS variable, listing space separated ELF
> section names that should be kept around instead of stripped, for
> example:
>
>   PACKAGE_KEEP_SECTIONS:pn-myrecipe = ".debug_frame"
>
> This variable is never applied to kernel modules, which are covered
> by CONFIG_UNWINDER_* instead.
>
> Add a oe-selftest case building core-image-minimal for qemuarm, and
> checking with readelf that busybox loses its .debug_frame section by
> default, but keeps it once PACKAGE_KEEP_SECTIONS is set.
>
> Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>
> ---

Hi Mathieu,

Thanks for your patch.

It looks like the added test is failing on the autobuilder:

2026-09-12 09:19:34,528 - oe-selftest - INFO - package.PackageKeepSections.test_package_keep_sections (subunit.RemotedTestCase)
2026-09-12 09:19:34,529 - oe-selftest - INFO -  ... ERROR
...
2026-09-12 09:19:34,529 - oe-selftest - INFO - 5: 28/54 531/772 (122.95s) (0 failed) (package.PackageKeepSections.test_package_keep_sections)
2026-09-12 09:19:34,529 - oe-selftest - INFO - testtools.testresult.real._StringException: Traceback (most recent call last):
  File "/srv/pokybuild/yocto-worker/oe-selftest-fedora/build/layers/openembedded-core/meta/lib/oeqa/selftest/cases/package.py", line 248, in test_package_keep_sections
    self.assertFalse(has_section(".debug_frame"),
                     ~~~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/srv/pokybuild/yocto-worker/oe-selftest-fedora/build/layers/openembedded-core/meta/lib/oeqa/selftest/cases/package.py", line 241, in has_section
    tar.extract("./usr/bin/busybox.nosuid", path=unpackedfs)
    ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/pokybuild/yocto-worker/oe-selftest-fedora/build/buildtools/sysroots/x86_64-pokysdk-linux/usr/lib/python3.13/tarfile.py", line 2365, in extract
    tarinfo = self._get_extract_tarinfo(member, filter_function, path)
  File "/srv/pokybuild/yocto-worker/oe-selftest-fedora/build/buildtools/sysroots/x86_64-pokysdk-linux/usr/lib/python3.13/tarfile.py", line 2372, in _get_extract_tarinfo
    tarinfo = self.getmember(member)
  File "/srv/pokybuild/yocto-worker/oe-selftest-fedora/build/buildtools/sysroots/x86_64-pokysdk-linux/usr/lib/python3.13/tarfile.py", line 2041, in getmember
    raise KeyError("filename %r not found" % name)
KeyError: "filename './usr/bin/busybox.nosuid' not found"

https://autobuilder.yoctoproject.org/valkyrie/#/builders/48/builds/4649
https://autobuilder.yoctoproject.org/valkyrie/#/builders/35/builds/4842

Can you have a look at the issue?

Thanks,
Mathieu

-- 
Mathieu Dubois-Briand, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com