Storing package metadata in ELF objects

Storing package metadata in ELF objects

[Luca Boccassi]

[-- Attachment #1: Type: text/plain, Size: 2496 bytes --]

Hello,

Cross-posting to the mailing lists of a few relevant projects.

After an initial discussion [0], recently we have been working on a new
specification [0] to encode rich package-level metadata inside ELF
objects, so that it can be included automatically in generated coredump
files. The prototype to parse this in systemd-coredump and store the
information in systemd-journal is ready for testing and merged
upstream. We are now seeking further comments/opinions/suggestions, as
we have a few months before the next release and thus there's plenty of
time to make incompatible changes to the format and implementation, if
required.

A proposal to use this by default for all packages built in Fedora 35
has been submitted [1].

The Fedora Wiki and the systemd.io document have more details, but to
make a long story short, a new .notes.package section with a JSON
payload will be included in ELF objects, encoding various package-
build-time information like distro name&version, package name&version,
etc.

To summarize from the discussion, the main reasons why we believe this
is useful are as following:

1) minimal containers: the rpm database is not installed in the
containers. The information about build-ids needs to be stored
externally, so package name information is not available immediately,
but only after offline processing. The new note doesn't depend on the
rpm db in any way.

2) handling of a core from a container, where the container and host
have different distros

3) self-built and external packages: unless a lot of care is taken to
keep access to the debuginfo packages, this information may be lost.
The new note is available even if the repository metadata gets lost.
Users can easily provide equivalent information in a format that makes
sense in their own environment. It should work even when rpms and debs
and other formats are mixed, e.g. during container image creation.

Other than in Fedora, we are already making the required code changes
at Microsoft to use the same format&specification for internally-built
binaries, and for tools that parse core files and logs.

Tools for RPM and DEB (debhelper) integration are also available [3].

-- 
Kind regards,
Luca Boccassi

[0] https://github.com/systemd/systemd/issues/18433
[1] https://systemd.io/COREDUMP_PACKAGE_METADATA/
[2] https://fedoraproject.org/wiki/Changes/Package_information_on_ELF_objects
[3] https://github.com/systemd/package-notes

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: Storing package metadata in ELF objects

[Luca Boccassi]

[-- Attachment #1: Type: text/plain, Size: 2493 bytes --]

On Sat, 2021-04-10 at 13:29 +0100, Luca Boccassi wrote:
> Hello,
> 
> Cross-posting to the mailing lists of a few relevant projects.
> 
> After an initial discussion [0], recently we have been working on a new
> specification [0] to encode rich package-level metadata inside ELF
> objects, so that it can be included automatically in generated coredump
> files. The prototype to parse this in systemd-coredump and store the
> information in systemd-journal is ready for testing and merged
> upstream. We are now seeking further comments/opinions/suggestions, as
> we have a few months before the next release and thus there's plenty of
> time to make incompatible changes to the format and implementation, if
> required.
> 
> A proposal to use this by default for all packages built in Fedora 35
> has been submitted [1].
> 
> The Fedora Wiki and the systemd.io document have more details, but to
> make a long story short, a new .notes.package section with a JSON
> payload will be included in ELF objects, encoding various package-
> build-time information like distro name&version, package name&version,
> etc.
> 
> To summarize from the discussion, the main reasons why we believe this
> is useful are as following:
> 
> 1) minimal containers: the rpm database is not installed in the
> containers. The information about build-ids needs to be stored
> externally, so package name information is not available immediately,
> but only after offline processing. The new note doesn't depend on the
> rpm db in any way.
> 
> 2) handling of a core from a container, where the container and host
> have different distros
> 
> 3) self-built and external packages: unless a lot of care is taken to
> keep access to the debuginfo packages, this information may be lost.
> The new note is available even if the repository metadata gets lost.
> Users can easily provide equivalent information in a format that makes
> sense in their own environment. It should work even when rpms and debs
> and other formats are mixed, e.g. during container image creation.
> 
> Other than in Fedora, we are already making the required code changes
> at Microsoft to use the same format&specification for internally-built
> binaries, and for tools that parse core files and logs.
> 
> Tools for RPM and DEB (debhelper) integration are also available [3].

Wrong Fedora list address - off to a great start already :-)
(fixed now)

-- 
Kind regards,
Luca Boccassi

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: Storing package metadata in ELF objects

[Zbigniew Jędrzejewski-Szmek]

[I'm forwarding the mail from Luca who is not subscribed to fedora-devel]

On Sat, Apr 10, 2021 at 01:38:31PM +0100, Luca Boccassi wrote:

Hello,

Cross-posting to the mailing lists of a few relevant projects.

After an initial discussion [0], recently we have been working on a new
specification [0] to encode rich package-level metadata inside ELF
objects, so that it can be included automatically in generated coredump
files. The prototype to parse this in systemd-coredump and store the
information in systemd-journal is ready for testing and merged
upstream. We are now seeking further comments/opinions/suggestions, as
we have a few months before the next release and thus there's plenty of
time to make incompatible changes to the format and implementation, if
required.

A proposal to use this by default for all packages built in Fedora 35
has been submitted [1].

The Fedora Wiki and the systemd.io document have more details, but to
make a long story short, a new .notes.package section with a JSON
payload will be included in ELF objects, encoding various package-
build-time information like distro name&version, package name&version,
etc.

To summarize from the discussion, the main reasons why we believe this
is useful are as following:

1) minimal containers: the rpm database is not installed in the
containers. The information about build-ids needs to be stored
externally, so package name information is not available immediately,
but only after offline processing. The new note doesn't depend on the
rpm db in any way.

2) handling of a core from a container, where the container and host
have different distros

3) self-built and external packages: unless a lot of care is taken to
keep access to the debuginfo packages, this information may be lost.
The new note is available even if the repository metadata gets lost.
Users can easily provide equivalent information in a format that makes
sense in their own environment. It should work even when rpms and debs
and other formats are mixed, e.g. during container image creation.

Other than in Fedora, we are already making the required code changes
at Microsoft to use the same format&specification for internally-built
binaries, and for tools that parse core files and logs.

Tools for RPM and DEB (debhelper) integration are also available [3].

> -- 
> Kind regards,
> Luca Boccassi

Re: Storing package metadata in ELF objects

[Mark Wielaard]

Hi,

On Sat, 2021-04-10 at 18:44 +0000, Zbigniew Jędrzejewski-Szmek wrote:
> [I'm forwarding the mail from Luca who is not subscribed to fedora-
> devel]
> On Sat, Apr 10, 2021 at 01:38:31PM +0100, Luca Boccassi wrote:
> Cross-posting to the mailing lists of a few relevant projects.

Note that in this version of the email the [N] references in your email
don't seem to point anywhere. I found an older variant of the same
email which contained:

[0] https://github.com/systemd/systemd/issues/18433
[1] https://systemd.io/COREDUMP_PACKAGE_METADATA/
[2] https://fedoraproject.org/wiki/Changes/Package_information_on_ELF_objects
[3] https://github.com/systemd/package-notes

> After an initial discussion [0], recently we have been working on a new
> specification [0] to encode rich package-level metadata inside ELF
> objects, so that it can be included automatically in generated coredump
> files. The prototype to parse this in systemd-coredump and store the
> information in systemd-journal is ready for testing and merged
> upstream. We are now seeking further comments/opinions/suggestions, as
> we have a few months before the next release and thus there's plenty of
> time to make incompatible changes to the format and implementation, if
> required.
> 
> A proposal to use this by default for all packages built in Fedora 35
> has been submitted [1].
> 
> The Fedora Wiki and the systemd.io document have more details, but to
> make a long story short, a new .notes.package section with a JSON
> payload will be included in ELF objects, encoding various package-
> build-time information like distro name&version, package
> name&version,
> etc.

Is there a list of default keys (and their canonical spelling, upper-
lower-Camel_Case, etc.)? If there is, could we have a "debuginfod" key
with as value an URL pointing to the debuginfod server URL where the
embedded build-id executable, debuginfo and sources can be found?
https://sourceware.org/elfutils/Debuginfod.html

> To summarize from the discussion, the main reasons why we believe this
> is useful are as following:
> 
> 1) minimal containers: the rpm database is not installed in the
> containers. The information about build-ids needs to be stored
> externally, so package name information is not available immediately,
> but only after offline processing. The new note doesn't depend on the
> rpm db in any way.
> 
> 2) handling of a core from a container, where the container and host
> have different distros
> 
> 3) self-built and external packages: unless a lot of care is taken to
> keep access to the debuginfo packages, this information may be lost.
> The new note is available even if the repository metadata gets lost.
> Users can easily provide equivalent information in a format that makes
> sense in their own environment. It should work even when rpms and debs
> and other formats are mixed, e.g. during container image creation.
> 
> Other than in Fedora, we are already making the required code changes
> at Microsoft to use the same format&specification for internally-built
> binaries, and for tools that parse core files and logs.
> 
> Tools for RPM and DEB (debhelper) integration are also available [3].
> 
> > -- 
> > Kind regards,
> > Luca Boccassi
> 
> 

Re: Storing package metadata in ELF objects

[Luca Boccassi]

[-- Attachment #1: Type: text/plain, Size: 3888 bytes --]

On Fri, 2021-04-30 at 19:57 +0200, Mark Wielaard wrote:
> Hi,
> 
> On Sat, 2021-04-10 at 18:44 +0000, Zbigniew Jędrzejewski-Szmek wrote:
> > [I'm forwarding the mail from Luca who is not subscribed to fedora-
> > devel]
> > On Sat, Apr 10, 2021 at 01:38:31PM +0100, Luca Boccassi wrote:
> > Cross-posting to the mailing lists of a few relevant projects.
> 
> Note that in this version of the email the [N] references in your email
> don't seem to point anywhere. I found an older variant of the same
> email which contained:
> 
> [0] https://github.com/systemd/systemd/issues/18433
> [1] https://systemd.io/COREDUMP_PACKAGE_METADATA/
> [2] https://fedoraproject.org/wiki/Changes/Package_information_on_ELF_objects
> [3] https://github.com/systemd/package-notes

Sorry about that! Must have messed up the copy&paste.

> > After an initial discussion [0], recently we have been working on a new
> > specification [0] to encode rich package-level metadata inside ELF
> > objects, so that it can be included automatically in generated coredump
> > files. The prototype to parse this in systemd-coredump and store the
> > information in systemd-journal is ready for testing and merged
> > upstream. We are now seeking further comments/opinions/suggestions, as
> > we have a few months before the next release and thus there's plenty of
> > time to make incompatible changes to the format and implementation, if
> > required.
> > 
> > A proposal to use this by default for all packages built in Fedora 35
> > has been submitted [1].
> > 
> > The Fedora Wiki and the systemd.io document have more details, but to
> > make a long story short, a new .notes.package section with a JSON
> > payload will be included in ELF objects, encoding various package-
> > build-time information like distro name&version, package
> > name&version,
> > etc.
> 
> Is there a list of default keys (and their canonical spelling, upper-
> lower-Camel_Case, etc.)? If there is, could we have a "debuginfod" key
> with as value an URL pointing to the debuginfod server URL where the
> embedded build-id executable, debuginfo and sources can be found?
> https://sourceware.org/elfutils/Debuginfod.html

The "Implementation" section of the spec lists the "main" fields:

https://systemd.io/COREDUMP_PACKAGE_METADATA/

(source for that is https://github.com/systemd/systemd/blob/main/docs/COREDUMP_PACKAGE_METADATA.md )

Would you like to send a PR to update it and add that field?

> > To summarize from the discussion, the main reasons why we believe this
> > is useful are as following:
> > 
> > 1) minimal containers: the rpm database is not installed in the
> > containers. The information about build-ids needs to be stored
> > externally, so package name information is not available immediately,
> > but only after offline processing. The new note doesn't depend on the
> > rpm db in any way.
> > 
> > 2) handling of a core from a container, where the container and host
> > have different distros
> > 
> > 3) self-built and external packages: unless a lot of care is taken to
> > keep access to the debuginfo packages, this information may be lost.
> > The new note is available even if the repository metadata gets lost.
> > Users can easily provide equivalent information in a format that makes
> > sense in their own environment. It should work even when rpms and debs
> > and other formats are mixed, e.g. during container image creation.
> > 
> > Other than in Fedora, we are already making the required code changes
> > at Microsoft to use the same format&specification for internally-built
> > binaries, and for tools that parse core files and logs.
> > 
> > Tools for RPM and DEB (debhelper) integration are also available [3].
> > 
> > > -- 
> > > Kind regards,
> > > Luca Boccassi

-- 
Kind regards,
Luca Boccassi

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: Storing package metadata in ELF objects

[Mark Wielaard]

[-- Attachment #1: Type: text/plain, Size: 1064 bytes --]

Hi Luca,

On Tue, 2021-05-04 at 14:43 +0100, Luca Boccassi wrote:
> On Fri, 2021-04-30 at 19:57 +0200, Mark Wielaard wrote:
> > Is there a list of default keys (and their canonical spelling, upper-
> > lower-Camel_Case, etc.)? If there is, could we have a "debuginfod" key
> > with as value an URL pointing to the debuginfod server URL where the
> > embedded build-id executable, debuginfo and sources can be found?
> > https://sourceware.org/elfutils/Debuginfod.html
> 
> The "Implementation" section of the spec lists the "main" fields:
> 
> https://systemd.io/COREDUMP_PACKAGE_METADATA/
> 
> (source for that is https://github.com/systemd/systemd/blob/main/docs/COREDUMP_PACKAGE_METADATA.md )
> 
> Would you like to send a PR to update it and add that field?

Sorry, I don't have a github account. But attached is a patch for to
document it and one for the package-notes generator to add an --
debuginfod argument (maybe the distro should set a default value for
that?) Hopefully those patches could be applied somehow.

Thanks,

Mark

[-- Attachment #2: 0001-docs-COREDUMP_PACKAGE_METADATA.md-Add-debuginfod-key.patch --]
[-- Type: text/x-patch, Size: 1462 bytes --]

From 176dde09fcfeff9bff97fbf65d47a641dbd2fa3a Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mark@klomp.org>
Date: Thu, 6 May 2021 03:05:02 +0200
Subject: [PATCH] docs/COREDUMP_PACKAGE_METADATA.md: Add debuginfod key

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 docs/COREDUMP_PACKAGE_METADATA.md | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/docs/COREDUMP_PACKAGE_METADATA.md b/docs/COREDUMP_PACKAGE_METADATA.md
index ab7c4596de..b7be9ca797 100644
--- a/docs/COREDUMP_PACKAGE_METADATA.md
+++ b/docs/COREDUMP_PACKAGE_METADATA.md
@@ -26,6 +26,10 @@ Thus it becomes desirable to add additional metadata to a binary at build time,
 `systemd-coredump` and other services analyzing core files are able to extract said
 metadata simply from the core file itself, without external dependencies.
 
+And in case external dependencies and network are available the core file
+should also include the debuginfod server URL that can provide the original
+executable, debuginfo and sources to facilitate debugging.
+
 ## Implementation
 
 This document will attempt to define a common metadata format specification, so that
@@ -58,6 +62,7 @@ Value: a JSON string with the structure described below
      "name":"coreutils",
      "version": "4711.0815.fc13.arm32",
      "osCpe":               # A CPE name for the operating system, `CPE_NAME` from os-release is a good default
+     "debuginfod": "https://debuginfod.fedoraproject.org"
 }
 ```
 
-- 
2.18.4


[-- Attachment #3: 0001-generate-package-notes.py-Add-debuginfod-argument.patch --]
[-- Type: text/x-patch, Size: 997 bytes --]

From 6264605699cbac02ed3060cc1ff6497b32e90382 Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mark@klomp.org>
Date: Thu, 6 May 2021 03:13:57 +0200
Subject: [PATCH] generate-package-notes.py: Add --debuginfod argument

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 generate-package-notes.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/generate-package-notes.py b/generate-package-notes.py
index c0b5d98..92126f7 100755
--- a/generate-package-notes.py
+++ b/generate-package-notes.py
@@ -71,6 +71,7 @@ def parse_args():
     p.add_argument('--package-version')
     p.add_argument('--cpe')
     p.add_argument('--rpm', metavar='NEVRA')
+    p.add_argument('--debuginfod')
 
     opts = p.parse_args()
 
@@ -143,6 +144,8 @@ def generate_section(opts):
     else:
         data['os'] = read_os_release('ID')
         data['osVersion'] = read_os_release('VERSION_ID')
+    if opts.debuginfod:
+        data['debuginfod'] = opts.debuginfod
 
     json = json_serialize(data)
 
-- 
2.18.4

Re: Storing package metadata in ELF objects

[Luca Boccassi]

[-- Attachment #1: Type: text/plain, Size: 1411 bytes --]

On Thu, 2021-05-06 at 03:17 +0200, Mark Wielaard wrote:
> Hi Luca,
> 
> On Tue, 2021-05-04 at 14:43 +0100, Luca Boccassi wrote:
> > On Fri, 2021-04-30 at 19:57 +0200, Mark Wielaard wrote:
> > > Is there a list of default keys (and their canonical spelling, upper-
> > > lower-Camel_Case, etc.)? If there is, could we have a "debuginfod" key
> > > with as value an URL pointing to the debuginfod server URL where the
> > > embedded build-id executable, debuginfo and sources can be found?
> > > https://sourceware.org/elfutils/Debuginfod.html
> > 
> > The "Implementation" section of the spec lists the "main" fields:
> > 
> > https://systemd.io/COREDUMP_PACKAGE_METADATA/
> > 
> > (source for that is https://github.com/systemd/systemd/blob/main/docs/COREDUMP_PACKAGE_METADATA.md )
> > 
> > Would you like to send a PR to update it and add that field?
> 
> Sorry, I don't have a github account. But attached is a patch for to
> document it and one for the package-notes generator to add an --
> debuginfod argument (maybe the distro should set a default value for
> that?) Hopefully those patches could be applied somehow.

Hi,

Thanks, opened PRs with your commits:

https://github.com/systemd/systemd/pull/19523
https://github.com/systemd/package-notes/pull/8

Yes, if the distro has a debuginfod server, it should definitely be
included.

-- 
Kind regards,
Luca Boccassi

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: Storing package metadata in ELF objects

[Guillem Jover]

On Sat, 2021-04-10 at 13:38:31 +0100, Luca Boccassi wrote:
> On Sat, 2021-04-10 at 13:29 +0100, Luca Boccassi wrote:
> > After an initial discussion [0], recently we have been working on a new
> > specification [0] to encode rich package-level metadata inside ELF
> > objects, so that it can be included automatically in generated coredump
> > files. The prototype to parse this in systemd-coredump and store the
> > information in systemd-journal is ready for testing and merged
> > upstream. We are now seeking further comments/opinions/suggestions, as
> > we have a few months before the next release and thus there's plenty of
> > time to make incompatible changes to the format and implementation, if
> > required.

I've skimmed over the discussion at [0], and while having this data
seems like it might be "nice", I've to agree with the comments there
voicing that there does not really seem to be an actual need and the
overhead and additional work do not seem worth it, TBH, at least
in the Debian context.

> > The Fedora Wiki and the systemd.io document have more details, but to
> > make a long story short, a new .notes.package section with a JSON
> > payload will be included in ELF objects, encoding various package-
> > build-time information like distro name&version, package name&version,
> > etc.
> > 
> > To summarize from the discussion, the main reasons why we believe this
> > is useful are as following:
> > 
> > 1) minimal containers: the rpm database is not installed in the
> > containers. The information about build-ids needs to be stored
> > externally, so package name information is not available immediately,
> > but only after offline processing. The new note doesn't depend on the
> > rpm db in any way.

In the Debian context, the build-ids data is going to be available
in the affected executables, and in debug symbols packages and the
Packages metaindices listing them, so there's no need for access to
any local dpkg database. Given that someone needing to install debug
packages will need access to those indices (either with outgoing network
access or with a repository mirror), these can be queried at that time.
Not to mention that AFAIR the Debian debug symbol servers make it
possible to query for specific build-ids.

> > 2) handling of a core from a container, where the container and host
> > have different distros

How each distribution handles debug packages and debug symbols is
going to be different, so it seems there will be a need for explicit
handling of these, at which point the above mentioned querying can be
implemented as well, w/o the need to encode the packaging data inside
the executable.

> > 3) self-built and external packages: unless a lot of care is taken to
> > keep access to the debuginfo packages, this information may be lost.
> > The new note is available even if the repository metadata gets lost.
> > Users can easily provide equivalent information in a format that makes
> > sense in their own environment. It should work even when rpms and debs
> > and other formats are mixed, e.g. during container image creation.

I'm not sure I see the problem here. Either these self-built 3rd-party
packages are kept in repos that also provide the debug symbols
somewhere for all historically released versions or these will not be
accessible anyway. If they are, they can as well be located as per
above from the Packages metaindices, and even if the repository
metadata gets lost, as long as the debug symbol packages are present
(if they are not what's the point anyway) the build-ids can always be
re-scanned from them as they are part of the Build-Ids field in the
.deb control file.

> > Other than in Fedora, we are already making the required code changes
> > at Microsoft to use the same format&specification for internally-built
> > binaries, and for tools that parse core files and logs.
> > 
> > Tools for RPM and DEB (debhelper) integration are also available [3].

So, to conclude, I don't really see the point of this in the Debian
context. (Not to mention the problems with encoding binary versions
that might be wrong, and the busy work involved.)

> > [0] https://github.com/systemd/systemd/issues/18433
> > [1] https://systemd.io/COREDUMP_PACKAGE_METADATA/
> > [2] https://fedoraproject.org/wiki/Changes/Package_information_on_ELF_objects
> > [3] https://github.com/systemd/package-notes

Thanks,
Guillem

Re: Storing package metadata in ELF objects

[Luca Boccassi]

[-- Attachment #1: Type: text/plain, Size: 7276 bytes --]

On Fri, 2021-05-14 at 12:41 +0200, Guillem Jover wrote:
> On Sat, 2021-04-10 at 13:38:31 +0100, Luca Boccassi wrote:
> > On Sat, 2021-04-10 at 13:29 +0100, Luca Boccassi wrote:
> > > After an initial discussion [0], recently we have been working on a new
> > > specification [0] to encode rich package-level metadata inside ELF
> > > objects, so that it can be included automatically in generated coredump
> > > files. The prototype to parse this in systemd-coredump and store the
> > > information in systemd-journal is ready for testing and merged
> > > upstream. We are now seeking further comments/opinions/suggestions, as
> > > we have a few months before the next release and thus there's plenty of
> > > time to make incompatible changes to the format and implementation, if
> > > required.
> 
> I've skimmed over the discussion at [0], and while having this data
> seems like it might be "nice", I've to agree with the comments there
> voicing that there does not really seem to be an actual need and the
> overhead and additional work do not seem worth it, TBH, at least
> in the Debian context.

Hi Guillem, thanks for having a look, much appreciated!

Just to clarify, the need is there - this is not an experimental
exercise, but it is borne out of an actual need&requirement, and it is
undergoing testing right now before deployment in a large scale
production infrastructure.
Not _everybody_ will need it, and not everywhere - that's absolutely
fair, and discussions on whether the ovearhead is worth it for
something that is not universally needed, but only in certain use
cases, is perfectly reasonable and welcome. I know Zbigniew is going to
try and get some raw numbers on the kind of overhead we are talking
about, that will hopefully help frame the discussion with more
precision.

> > > The Fedora Wiki and the systemd.io document have more details, but to
> > > make a long story short, a new .notes.package section with a JSON
> > > payload will be included in ELF objects, encoding various package-
> > > build-time information like distro name&version, package name&version,
> > > etc.
> > > 
> > > To summarize from the discussion, the main reasons why we believe this
> > > is useful are as following:
> > > 
> > > 1) minimal containers: the rpm database is not installed in the
> > > containers. The information about build-ids needs to be stored
> > > externally, so package name information is not available immediately,
> > > but only after offline processing. The new note doesn't depend on the
> > > rpm db in any way.
> 
> In the Debian context, the build-ids data is going to be available
> in the affected executables, and in debug symbols packages and the
> Packages metaindices listing them, so there's no need for access to
> any local dpkg database. Given that someone needing to install debug
> packages will need access to those indices (either with outgoing network
> access or with a repository mirror), these can be queried at that time.
> Not to mention that AFAIR the Debian debug symbol servers make it
> possible to query for specific build-ids.

This is not strictly related to debug packages, though? In fact, on
systems where this could be of most use you explicitly do _not_ install
debug packages (or anything at all). Or even if you wanted to, you
could not - corefiles are not handled inside the container, but
outside. Even if you wanted to and were allowed to (which for many
environments it's not the case), you can't install a Debian debug
package on a CoreOS host or Mariner host or a Flatcar host.

> > > 2) handling of a core from a container, where the container and host
> > > have different distros
> 
> How each distribution handles debug packages and debug symbols is
> going to be different, so it seems there will be a need for explicit
> handling of these, at which point the above mentioned querying can be
> implemented as well, w/o the need to encode the packaging data inside
> the executable.

Again, matching to debug symbols is not the main goal here, build-id
works for that. The main goal is to have useful metadata immediately
available in all occasions, regardless of where the core was generated
on the host, without reaching out to external services, so that it is
directly included and collated in the system journal when the core file
is handled.

With a common metadata definition, there's no need to query or
explicitly handle anything - this already works if you use systemd-
coredump built from the main branch, and handle a core file from
different containers running different distros with binaries having
this metadata in the ELF file, and it just works. This is tested, not
theoretical.

> > > 3) self-built and external packages: unless a lot of care is taken to
> > > keep access to the debuginfo packages, this information may be lost.
> > > The new note is available even if the repository metadata gets lost.
> > > Users can easily provide equivalent information in a format that makes
> > > sense in their own environment. It should work even when rpms and debs
> > > and other formats are mixed, e.g. during container image creation.
> 
> I'm not sure I see the problem here. Either these self-built 3rd-party
> packages are kept in repos that also provide the debug symbols
> somewhere for all historically released versions or these will not be
> accessible anyway. If they are, they can as well be located as per
> above from the Packages metaindices, and even if the repository
> metadata gets lost, as long as the debug symbol packages are present
> (if they are not what's the point anyway) the build-ids can always be
> re-scanned from them as they are part of the Build-Ids field in the
> .deb control file.

I think you are thinking about being confined to single distro here - I
am talking about mixed environments. Maybe the build-id can be used to
trace it back - maybe it is available on some federated server. Most
likely it is not, in these cases - it would require customers to go and
upload their sources and symbols and information to random third party
services, a bit unlikely. You have no reference that indicates where to
go look for. Just a filename, which can be anything, and a random id
which might never be published anywhere. What do you do with it?

> > > Other than in Fedora, we are already making the required code changes
> > > at Microsoft to use the same format&specification for internally-built
> > > binaries, and for tools that parse core files and logs.
> > > 
> > > Tools for RPM and DEB (debhelper) integration are also available [3].
> 
> So, to conclude, I don't really see the point of this in the Debian
> context. (Not to mention the problems with encoding binary versions
> that might be wrong, and the busy work involved.)

Sorry, what do you mean here by encoding binary versions?

> > > [0] https://github.com/systemd/systemd/issues/18433
> > > [1] https://systemd.io/COREDUMP_PACKAGE_METADATA/
> > > [2] https://fedoraproject.org/wiki/Changes/Package_information_on_ELF_objects
> > > [3] https://github.com/systemd/package-notes
> 
> Thanks,
> Guillem

-- 
Kind regards,
Luca Boccassi

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: Storing package metadata in ELF objects

[Guillem Jover]

On Fri, 2021-05-14 at 14:41:32 +0100, Luca Boccassi wrote:
> On Fri, 2021-05-14 at 12:41 +0200, Guillem Jover wrote:
> > On Sat, 2021-04-10 at 13:38:31 +0100, Luca Boccassi wrote:
> > > On Sat, 2021-04-10 at 13:29 +0100, Luca Boccassi wrote:
> > > > After an initial discussion [0], recently we have been working on a new
> > > > specification [0] to encode rich package-level metadata inside ELF
> > > > objects, so that it can be included automatically in generated coredump
> > > > files. The prototype to parse this in systemd-coredump and store the
> > > > information in systemd-journal is ready for testing and merged
> > > > upstream. We are now seeking further comments/opinions/suggestions, as
> > > > we have a few months before the next release and thus there's plenty of
> > > > time to make incompatible changes to the format and implementation, if
> > > > required.
> > 
> > I've skimmed over the discussion at [0], and while having this data
> > seems like it might be "nice", I've to agree with the comments there
> > voicing that there does not really seem to be an actual need and the
> > overhead and additional work do not seem worth it, TBH, at least
> > in the Debian context.

> Hi Guillem, thanks for having a look, much appreciated!
> 
> Just to clarify, the need is there - this is not an experimental
> exercise, but it is borne out of an actual need&requirement, and it is
> undergoing testing right now before deployment in a large scale
> production infrastructure.
> Not _everybody_ will need it, and not everywhere - that's absolutely
> fair, and discussions on whether the ovearhead is worth it for
> something that is not universally needed, but only in certain use
> cases, is perfectly reasonable and welcome. I know Zbigniew is going to
> try and get some raw numbers on the kind of overhead we are talking
> about, that will hopefully help frame the discussion with more
> precision.

Sorry, I think I expressed myself sloppily. My impression is not
that there's no need behind this, but that there's no need for this
specific implementation at least in the Debian context, as I think
the information should be already available by other means.

Also when I mentioned overhead here, it was more about packaging and
integration work than say actual size increase, even though that might
have an adverse effect on .udeb's for example, and perhaps a
non-insignificant one on .deb's depending on the amount of objects
included.

> > > > The Fedora Wiki and the systemd.io document have more details, but to
> > > > make a long story short, a new .notes.package section with a JSON
> > > > payload will be included in ELF objects, encoding various package-
> > > > build-time information like distro name&version, package name&version,
> > > > etc.
> > > > 
> > > > To summarize from the discussion, the main reasons why we believe this
> > > > is useful are as following:
> > > > 
> > > > 1) minimal containers: the rpm database is not installed in the
> > > > containers. The information about build-ids needs to be stored
> > > > externally, so package name information is not available immediately,
> > > > but only after offline processing. The new note doesn't depend on the
> > > > rpm db in any way.
> > 
> > In the Debian context, the build-ids data is going to be available
> > in the affected executables, and in debug symbols packages and the
> > Packages metaindices listing them, so there's no need for access to
> > any local dpkg database. Given that someone needing to install debug
> > packages will need access to those indices (either with outgoing network
> > access or with a repository mirror), these can be queried at that time.
> > Not to mention that AFAIR the Debian debug symbol servers make it
> > possible to query for specific build-ids.
> 
> This is not strictly related to debug packages, though?

That was actually the impression I was getting from reading the refs
though. :) But I'll expand below.

> In fact, on
> systems where this could be of most use you explicitly do _not_ install
> debug packages (or anything at all). Or even if you wanted to, you
> could not - corefiles are not handled inside the container, but
> outside. Even if you wanted to and were allowed to (which for many
> environments it's not the case), you can't install a Debian debug
> package on a CoreOS host or Mariner host or a Flatcar host.

Sure, but precisely dbgsym .deb's are the things that are trivial to
unpack with dpkg-deb (or ar+tar) w/o needing to actually install them.

> > > > 2) handling of a core from a container, where the container and host
> > > > have different distros
> > 
> > How each distribution handles debug packages and debug symbols is
> > going to be different, so it seems there will be a need for explicit
> > handling of these, at which point the above mentioned querying can be
> > implemented as well, w/o the need to encode the packaging data inside
> > the executable.
> 
> Again, matching to debug symbols is not the main goal here, build-id
> works for that. The main goal is to have useful metadata immediately
> available in all occasions, regardless of where the core was generated
> on the host, without reaching out to external services, so that it is
> directly included and collated in the system journal when the core file
> is handled.
> 
> With a common metadata definition, there's no need to query or
> explicitly handle anything - this already works if you use systemd-
> coredump built from the main branch, and handle a core file from
> different containers running different distros with binaries having
> this metadata in the ELF file, and it just works. This is tested, not
> theoretical.

So this is where I guess I'm missing something. To be able to make
sense of the coredumps there are two things that might end up being
relevant, backtraces and source code. systemd-coredump might already
emit a backtrace, and depending on the information provided it might
be more or less useful. If one needs the actual debug symbols there's
already some external querying/fetching required, and if distribution
specific source code is required because many distributions patch
upstream source, then even more querying/fetching will be required.

Which is why I'm not seeing why this standalone and isolated metadata
would be of much help by itself. As in, the way I see it, either the
information from systemd (w/o the extra metadata) is sufficient to
track down bugs, or that querying/fetching would be needed anyway, at
which point the metadata can be inferred too then?

> > > > 3) self-built and external packages: unless a lot of care is taken to
> > > > keep access to the debuginfo packages, this information may be lost.
> > > > The new note is available even if the repository metadata gets lost.
> > > > Users can easily provide equivalent information in a format that makes
> > > > sense in their own environment. It should work even when rpms and debs
> > > > and other formats are mixed, e.g. during container image creation.
> > 
> > I'm not sure I see the problem here. Either these self-built 3rd-party
> > packages are kept in repos that also provide the debug symbols
> > somewhere for all historically released versions or these will not be
> > accessible anyway. If they are, they can as well be located as per
> > above from the Packages metaindices, and even if the repository
> > metadata gets lost, as long as the debug symbol packages are present
> > (if they are not what's the point anyway) the build-ids can always be
> > re-scanned from them as they are part of the Build-Ids field in the
> > .deb control file.
> 
> I think you are thinking about being confined to single distro here - I
> am talking about mixed environments. Maybe the build-id can be used to
> trace it back - maybe it is available on some federated server. Most
> likely it is not, in these cases - it would require customers to go and
> upload their sources and symbols and information to random third party
> services, a bit unlikely. You have no reference that indicates where to
> go look for. Just a filename, which can be anything, and a random id
> which might never be published anywhere. What do you do with it?

Oh, I was thinking about those mixed environments, full chroots or
stripped down containers, from different vendors, but affecting Debian
installations. What I'm also probably missing here is how does the
metadata help for a third-party that is not expected to track/keep/upload
debug symbols nor source packages into some repository, because otherwise
I'm not seeing how they'd make use of the cores (if they are insufficient
by themselves) to debug issues? I guess my question back would be what
would they do with the metadata if they do not have the debug symbols
nor the sources readily available? Also assuming of course they exercise
good practices such as never reusing the same package-version-arch tuple
for different builds, and similar. :)

> > > > Other than in Fedora, we are already making the required code changes
> > > > at Microsoft to use the same format&specification for internally-built
> > > > binaries, and for tools that parse core files and logs.
> > > > 
> > > > Tools for RPM and DEB (debhelper) integration are also available [3].
> > 
> > So, to conclude, I don't really see the point of this in the Debian
> > context. (Not to mention the problems with encoding binary versions
> > that might be wrong, and the busy work involved.)
> 
> Sorry, what do you mean here by encoding binary versions?

(Expanding, although I assume most of this you already know, but just
for context's sake.)

As was mentioned on the systemd issue (AFAIR), the binary version for
a .deb is decided by the packaging and can (and does) vary from the
source version, and that information is generated after the programs
have been compiled.

For a source version 2.0-1, there are two types of diverging binary
versions, one is for binary-only non-maintainer-uploads (binNMU), such
as 2.0-1+b3 (this would be known at compile-time), and the other would
be for a different binary version-space such as 3:4.5-1 (which is
unknown at compile-time). Both can end up being combined too, as in
3:4.5-1+b5.

Thanks,
Guillem

Re: Storing package metadata in ELF objects

[Mark Wielaard]

Hi Guillem,

On Wed, 2021-05-19 at 02:19 +0200, Guillem Jover wrote:
> So this is where I guess I'm missing something. To be able to make
> sense of the coredumps there are two things that might end up being
> relevant, backtraces and source code. systemd-coredump might already
> emit a backtrace, and depending on the information provided it might
> be more or less useful. If one needs the actual debug symbols there's
> already some external querying/fetching required, and if distribution
> specific source code is required because many distributions patch
> upstream source, then even more querying/fetching will be required.
> 
> Which is why I'm not seeing why this standalone and isolated metadata
> would be of much help by itself. As in, the way I see it, either the
> information from systemd (w/o the extra metadata) is sufficient to
> track down bugs, or that querying/fetching would be needed anyway, at
> which point the metadata can be inferred too then?

Because without that metadata you cannot easily figure out where/how to
get the files needed to properly track down the bugs. But using that
metadata you can figure out where the debuginfod server is that can
provide all that information for the binaries/core files (or a distro
specific method if the distributor doesn't have a debuginfod server
yet).

> Oh, I was thinking about those mixed environments, full chroots or
> stripped down containers, from different vendors, but affecting Debian
> installations. What I'm also probably missing here is how does the
> metadata help for a third-party that is not expected to track/keep/upload
> debug symbols nor source packages into some repository, because otherwise
> I'm not seeing how they'd make use of the cores (if they are insufficient
> by themselves) to debug issues? I guess my question back would be what
> would they do with the metadata if they do not have the debug symbols
> nor the sources readily available? Also assuming of course they exercise
> good practices such as never reusing the same package-version-arch tuple
> for different builds, and similar. :)

Different builds will have different build-ids, so they can be kept
apart. But even if without the distributor having added debuginfod
meta-data and providing a server to fetch the extra symbols, debuginfo,
sources, the extra meta-data is useful to administrators. Just seeing
that crashes are associated with specific distro/version/packages helps
narrow down instabilities.

Cheers,

Mark

Re: Storing package metadata in ELF objects

[Luca Boccassi]

[-- Attachment #1: Type: text/plain, Size: 4510 bytes --]

On Wed, 2021-05-19 at 16:58 +0200, Mark Wielaard wrote:
> Hi Guillem,
> 
> On Wed, 2021-05-19 at 02:19 +0200, Guillem Jover wrote:
> > So this is where I guess I'm missing something. To be able to make
> > sense of the coredumps there are two things that might end up being
> > relevant, backtraces and source code. systemd-coredump might already
> > emit a backtrace, and depending on the information provided it might
> > be more or less useful. If one needs the actual debug symbols there's
> > already some external querying/fetching required, and if distribution
> > specific source code is required because many distributions patch
> > upstream source, then even more querying/fetching will be required.
> > 
> > Which is why I'm not seeing why this standalone and isolated metadata
> > would be of much help by itself. As in, the way I see it, either the
> > information from systemd (w/o the extra metadata) is sufficient to
> > track down bugs, or that querying/fetching would be needed anyway, at
> > which point the metadata can be inferred too then?
> 
> Because without that metadata you cannot easily figure out where/how to
> get the files needed to properly track down the bugs. But using that
> metadata you can figure out where the debuginfod server is that can
> provide all that information for the binaries/core files (or a distro
> specific method if the distributor doesn't have a debuginfod server
> yet).

Yes, that is a good use case. Another use case is that the person (or
bot) who first looks at the journal with the crash notification and the
metadata might not necessarily be the one that does the full in-depth
debugging. First level support will look at things and go "oh this is
from package X at version Y, therefore team Z needs to chime in".
Or it can see that it's version A.B.C, which is listed as known buggy,
and ignore the issue. Or a myriad of other combinations.

Then there are automated systems, parsing logs and creating tickets.
Having the structured metadata available in the journal in the crash
message means much more complex and useful querying and ticket creation
systems can be set up. You _cannot_ just go and query random remote
internet servers from these systems, they need to be network-isolated,
as logs can have confidential data from customers.

The main point is, there are many many things that happen between a
crash and the team owning the component looking up debugging symbols
and loading core files. This feature is very very useful for a whole
lot of those things.

> > Oh, I was thinking about those mixed environments, full chroots or
> > stripped down containers, from different vendors, but affecting Debian
> > installations. What I'm also probably missing here is how does the
> > metadata help for a third-party that is not expected to track/keep/upload
> > debug symbols nor source packages into some repository, because otherwise
> > I'm not seeing how they'd make use of the cores (if they are insufficient
> > by themselves) to debug issues? I guess my question back would be what
> > would they do with the metadata if they do not have the debug symbols
> > nor the sources readily available? Also assuming of course they exercise
> > good practices such as never reusing the same package-version-arch tuple
> > for different builds, and similar. :)
> 
> Different builds will have different build-ids, so they can be kept
> apart. But even if without the distributor having added debuginfod
> meta-data and providing a server to fetch the extra symbols, debuginfo,
> sources, the extra meta-data is useful to administrators. Just seeing
> that crashes are associated with specific distro/version/packages helps
> narrow down instabilities.

Precisely - again this is a very much real use case. In my case, the
engineers doing support and looking at the logs (and only at the logs -
no access to the running systems is permitted) _want_ this, because it
helps them. Being able to know at a glance to the journal exactly what
is borken, with version info, is extremely valuable to them.

Yes the version info might not be precise for a minority of use cases
that override the binary version with something different than the
source version, but that's fine as it's far and few, mostly affects
metapackages, and even then it can be documented clearly that the
reference is to the source version, not the binary one.

-- 
Kind regards,
Luca Boccassi

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]