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+---
+title: Package Metadata for Core Files
+category: Interfaces
+layout: default
+---
+
+# 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 ELF header section, in a key-value JSON
+format. Implementers working on parsing core files should not assume a specific list of
+keys, but parse anything that is included in the section.
+Implementers working on build tools should strive to use the same key 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.
+
+* Section header
+
+```
+SECTION: `.note.package`
+node-id: `0xcafe1a7e`
+Owner: `FDO` (FreeDesktop.org)
+Value: a JSON string with the structure described below
+```
+
+* JSON payload
+
+```json
+{
+     "packageType":"rpm",          # this provides a namespace for the package+package-version fields
+     "packageDistro":"fedora",
+     "packageDistroVersion":"33",
+     "package":"coreutils",
+     "packageVersion": "4711.0815.fc13.arm32",
+     "cpe":                        # A CPE name for the operating system, `CPE_NAME` from os-release is a good default
+}
+```
+
+A reference implementations of a [build-time tool is provided](https://github.com/keszybz/rpm-version-note/)
+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.fc34
+SECTIONS
+{
+    .note.package : ALIGN(4) {
+        BYTE(0x04) BYTE(0x00) BYTE(0x00) BYTE(0x00) /* Length of Owner including NUL */
+        BYTE(0x73) BYTE(0x00) BYTE(0x00) BYTE(0x00) /* Length of Value including NUL */
+        BYTE(0x7e) BYTE(0x1a) BYTE(0xfe) BYTE(0xca) /* Note ID */
+        BYTE(0x46) BYTE(0x44) BYTE(0x4f) BYTE(0x00) /* Owner: 'FDO\x00' */
+        BYTE(0x7b) BYTE(0x22) BYTE(0x70) BYTE(0x61) /* Value: '{"packageType":"rpm","package":"systemd","packageVersion":"248~rc2-1.fc34","cpe":"cpe:/o:fedoraproject:fedora:33"}\x00\x00' */
+        BYTE(0x63) BYTE(0x6b) BYTE(0x61) BYTE(0x67)
+        BYTE(0x65) BYTE(0x54) BYTE(0x79) BYTE(0x70)
+        BYTE(0x65) BYTE(0x22) BYTE(0x3a) BYTE(0x22)
+        BYTE(0x72) BYTE(0x70) BYTE(0x6d) BYTE(0x22)
+        BYTE(0x2c) BYTE(0x22) BYTE(0x70) BYTE(0x61)
+        BYTE(0x63) BYTE(0x6b) BYTE(0x61) BYTE(0x67)
+        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(0x70) BYTE(0x61)
+        BYTE(0x63) BYTE(0x6b) BYTE(0x61) BYTE(0x67)
+        BYTE(0x65) BYTE(0x56) 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(0x34) BYTE(0x22) BYTE(0x2c) BYTE(0x22)
+        BYTE(0x63) 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;
+```