docs: rename COREDUMP_PACKAGE_METADATA → ELF_PACKAGE_METADATA

The format described by this document is used not only for coredumps,
but also for other purposes, so we've outgrown the old title.

A redirect was added based on https://codepo8.github.io/github-redirection-demo/.
I tried to use a relative link, but it's hard to test if it works
before merging.

Co-authored-by: Benjamin Franzke <benjaminfranzke@googlemail.com>

1 files changed, 149 insertions, 0 deletions

diff --git a/docs/ELF_PACKAGE_METADATA.md b/docs/ELF_PACKAGE_METADATA.md
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+---
+title: Package Metadata for ELF Files
+category: Interfaces
+layout: default
+SPDX-License-Identifier: LGPL-2.1-or-later
+---
+
+# Package Metadata for Core Files
+
+*Intended audience: hackers working on userspace subsystems that create ELF binaries
+or parse ELF core files.*
+
+## Motivation
+
+ELF binaries get stamped with a unique, build-time generated hex string identifier called
+`build-id`, [which gets embedded as an ELF note called `.note.gnu.build-id`](https://fedoraproject.org/wiki/Releases/FeatureBuildId).
+In most cases, this allows to associate a stripped binary with its debugging information.
+It is used, for example, to dynamically fetch DWARF symbols from a debuginfo server, or
+to query the local package manager and find out the package metadata or, again, the DWARF
+symbols or program sources.
+
+However, this usage of the `build-id` requires either local metadata, usually set up by
+the package manager, or access to a remote server over the network. Both of those might
+be unavailable or forbidden.
+
+Thus it becomes desirable to add additional metadata to a binary at build time, so that
+`systemd-coredump` and other services analyzing core files are able to extract said
+metadata simply from the core file itself, without external dependencies.
+
+## Implementation
+
+This document will attempt to define a common metadata format specification, so that
+multiple implementers might use it when building packages, or core file analyzers, and
+so on.
+
+The metadata will be embedded in a single, new, 4-bytes-aligned, allocated, 0-padded,
+read-only ELF header section, in a name-value JSON object format. Implementers working on parsing
+core files should not assume a specific list of names, but parse anything that is included
+in the section, and should look for the note using the `note type`. Implementers working on
+build tools should strive to use the same names, for consistency. The most common will be
+listed here. When corresponding to the content of os-release, the values should match, again for consistency.
+
+If available, the metadata should also include the debuginfod server URL that can provide
+the original executable, debuginfo and sources, to further facilitate debugging.
+
+* Section header
+
+```
+SECTION: `.note.package`
+note type: `0xcafe1a7e`
+Owner: `FDO` (FreeDesktop.org)
+Value: a single JSON object encoded as a zero-terminated UTF-8 string
+```
+
+* JSON payload
+
+```json
+{
+     "type":"rpm",          # this provides a namespace for the package+package-version fields
+     "os":"fedora",
+     "osVersion":"33",
+     "name":"coreutils",
+     "version":"4711.0815.fc13",
+     "architecture":"arm32",
+     "osCpe": "cpe:/o:fedoraproject:fedora:33",          # A CPE name for the operating system, `CPE_NAME` from os-release is a good default
+     "debugInfoUrl": "https://debuginfod.fedoraproject.org/"
+}
+```
+
+The format is a single JSON object, encoded as a zero-terminated `UTF-8` string.
+Each name in the object shall be unique as per recommendations of
+[RFC8259](https://datatracker.ietf.org/doc/html/rfc8259#section-4). Strings shall
+not contain any control character, nor use `\uXXX` escaping.
+
+When it comes to JSON numbers, this specification assumes that JSON parsers
+processing this information are capable of reproducing the full signed 53bit
+integer range (i.e. -2⁵³+1…+2⁵³-1) as well as the full 64bit IEEE floating
+point number range losslessly (with the exception of NaN/-inf/+inf, since JSON
+cannot encode that), as per recommendations of
+[RFC8259](https://datatracker.ietf.org/doc/html/rfc8259#page-8). Fields in
+these JSON objects are thus permitted to encode numeric values from these
+ranges as JSON numbers, and should not use numeric values not covered by these
+types and ranges.
+
+A reference implementations of a [build-time tool is provided](https://github.com/systemd/package-notes)
+and can be used to generate a linker script, which can then be used at build time via
+```LDFLAGS="-Wl,-T,/path/to/generated/script"``` to include the note in the binary.
+
+Generator:
+```console
+$ ./generate-package-notes.py --rpm systemd-248~rc2-1.fc33.arm32 --cpe cpe:/o:fedoraproject:fedora:33
+SECTIONS
+{
+    .note.package (READONLY) : ALIGN(4) {
+        LONG(0x0004)                                /* Length of Owner including NUL */
+        LONG(0x007b)                                /* Length of Value including NUL */
+        LONG(0xcafe1a7e)                            /* Note ID */
+        BYTE(0x46) BYTE(0x44) BYTE(0x4f) BYTE(0x00) /* Owner: 'FDO\x00' */
+        BYTE(0x7b) BYTE(0x22) BYTE(0x74) BYTE(0x79) /* Value: '{"type":"rpm","name":"systemd","version":"248~rc2-1.fc33","architecture":"arm32","osCpe":"cpe:/o:fedoraproject:fedora:33"}\x00\x00' */
+        BYTE(0x70) BYTE(0x65) BYTE(0x22) BYTE(0x3a)
+        BYTE(0x22) BYTE(0x72) BYTE(0x70) BYTE(0x6d)
+        BYTE(0x22) BYTE(0x2c) BYTE(0x22) BYTE(0x6e)
+        BYTE(0x61) BYTE(0x6d) BYTE(0x65) BYTE(0x22)
+        BYTE(0x3a) BYTE(0x22) BYTE(0x73) BYTE(0x79)
+        BYTE(0x73) BYTE(0x74) BYTE(0x65) BYTE(0x6d)
+        BYTE(0x64) BYTE(0x22) BYTE(0x2c) BYTE(0x22)
+        BYTE(0x76) BYTE(0x65) BYTE(0x72) BYTE(0x73)
+        BYTE(0x69) BYTE(0x6f) BYTE(0x6e) BYTE(0x22)
+        BYTE(0x3a) BYTE(0x22) BYTE(0x32) BYTE(0x34)
+        BYTE(0x38) BYTE(0x7e) BYTE(0x72) BYTE(0x63)
+        BYTE(0x32) BYTE(0x2d) BYTE(0x31) BYTE(0x2e)
+        BYTE(0x66) BYTE(0x63) BYTE(0x33) BYTE(0x33)
+        BYTE(0x22) BYTE(0x2c) BYTE(0x22) BYTE(0x61)
+        BYTE(0x72) BYTE(0x63) BYTE(0x68) BYTE(0x69)
+        BYTE(0x74) BYTE(0x65) BYTE(0x63) BYTE(0x74)
+        BYTE(0x75) BYTE(0x72) BYTE(0x65) BYTE(0x22)
+        BYTE(0x3a) BYTE(0x22) BYTE(0x61) BYTE(0x72)
+        BYTE(0x6d) BYTE(0x33) BYTE(0x32) BYTE(0x22)
+        BYTE(0x2c) BYTE(0x22) BYTE(0x6f) BYTE(0x73)
+        BYTE(0x43) BYTE(0x70) BYTE(0x65) BYTE(0x22)
+        BYTE(0x3a) BYTE(0x22) BYTE(0x63) BYTE(0x70)
+        BYTE(0x65) BYTE(0x3a) BYTE(0x2f) BYTE(0x6f)
+        BYTE(0x3a) BYTE(0x66) BYTE(0x65) BYTE(0x64)
+        BYTE(0x6f) BYTE(0x72) BYTE(0x61) BYTE(0x70)
+        BYTE(0x72) BYTE(0x6f) BYTE(0x6a) BYTE(0x65)
+        BYTE(0x63) BYTE(0x74) BYTE(0x3a) BYTE(0x66)
+        BYTE(0x65) BYTE(0x64) BYTE(0x6f) BYTE(0x72)
+        BYTE(0x61) BYTE(0x3a) BYTE(0x33) BYTE(0x33)
+        BYTE(0x22) BYTE(0x7d) BYTE(0x00) BYTE(0x00)
+    }
+}
+INSERT AFTER .note.gnu.build-id;
+```
+
+## Well-known keys
+
+The metadata format is intentionally left open, so that vendors can add their own information.
+A set of well-known keys is defined here, and hopefully shared among all vendors.
+
+| Key name     | Key description                                                          | Example value                         |
+|--------------|--------------------------------------------------------------------------|---------------------------------------|
+| type         | The packaging type                                                       | rpm                                   |
+| os           | The OS name, typically corresponding to ID in os-release                 | fedora                                |
+| osVersion    | The OS version, typically corresponding to VERSION_ID in os-release      | 33                                    |
+| name         | The source package name                                                  | coreutils                             |
+| version      | The source package version                                               | 4711.0815.fc13                        |
+| architecture | The binary package architecture                                          | arm32                                 |
+| osCpe        | A CPE name for the OS, typically corresponding to CPE_NAME in os-release | cpe:/o:fedoraproject:fedora:33        |
+| debugInfoUrl | The debuginfod server url, if available                                  | https://debuginfod.fedoraproject.org/ |