RFC: Add ELF note for description with JSON data

[Sebastian Huber]

Hello,

I would like to add some metadata to executable ELF files for the RTEMS 
real-time operating system. It seems that ELF notes are a good way to do 
this. Would it be possible to add a standard or GNU-specific note type 
for descriptions which contain data in JSON format? This would help to 
use standard tools such as readelf to get the descriptions of such 
notes. For example:

diff --git a/include/elf/common.h b/include/elf/common.h
index 6f64f05890c..95d6068178f 100644
--- a/include/elf/common.h
+++ b/include/elf/common.h
@@ -824,6 +824,7 @@
  #define NT_GNU_BUILD_ID                3       /* Generated by ld 
--build-id.  */
  #define NT_GNU_GOLD_VERSION    4       /* Generated by gold.  */
  #define NT_GNU_PROPERTY_TYPE_0  5      /* Generated by gcc.  */
+#define NT_GNU_JSON            6       /* Contains arbitrary JSON data.  */

  #define NT_GNU_BUILD_ATTRIBUTE_OPEN    0x100
  #define NT_GNU_BUILD_ATTRIBUTE_FUNC    0x101


$ readelf -n --format=json file.elf
{"note-sections": [
   {"section": ".note.gnu.json", "notes": [
     {"name": "GNU",
      "type": 6,
      "type-info": "NT_GNU_JSON",
      "description": {"key": "value"}}]}

The note was produced by:

.pushsection .note.gnu.json , "", %note
.balign 4
.long 2f - 1f
.long 4f - 3f
.long 6
1: .asciz "GNU"
2: .balign 4
3: .asciz "{\"key\": \"value\"}"
4: .balign 4
.popsection

A basic support would require the allocation of a node type number and a 
new type-specific output.

Optionally, we could add JSON output to readelf. One option would be to 
do this using libxo:

https://juniper.github.io/libxo/libxo-manual.html

Would such a feature acceptable in general?

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Herr Sebastian HUBER
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