[lldb] Document SymbolFileJSON

[JDevlieghere]

I've had multiple request for documentation about the JSON symbol file format that LLDB supports. This patch documents the structure and fields, shows a handful of examples and explains how to use it in LLDB.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Jonas Devlieghere (JDevlieghere)

Changes

I've had multiple request for documentation about the JSON symbol file format that LLDB supports. This patch documents the structure and fields, shows a handful of examples and explains how to use it in LLDB.

---

Full diff: https://github.com/llvm/llvm-project/pull/112938.diff

1 Files Affected:

• (added) lldb/docs/resources/symbolfilejson.rst (+201)

diff --git a/lldb/docs/resources/symbolfilejson.rst b/lldb/docs/resources/symbolfilejson.rst
new file mode 100644
index 00000000000000..54f606ce1ffd58
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+++ b/lldb/docs/resources/symbolfilejson.rst
@@ -0,0 +1,201 @@
+JSON Symbol File Format
+=======================
+
+The JSON symbol file format encodes symbols in a text based, human readable
+format. JSON symbol files can be used to symbolicate programs that miss symbol
+information, for example because they have been stripped.
+
+Format
+------
+
+The symbol file contains of a single JSON object with the following top level
+keys:
+
+* ``triple``
+* ``uuid``
+* ``type``
+* ``sections``
+* ``symbols``
+
+The ``triple``, ``uuid`` and ``type`` form the header and should therefore come
+first. The ``type`` field is optional. The body consists ``sections`` and
+``symbols``, each represented as a JSON array. Both arrays are optional, and
+can be omitted and are allowed to be empty.
+
+triple
+``````
+
+The triple is a string with the triple of the object file it corresponds to.
+The triple follows the same format as used by LLVM:
+``<arch><sub>-<vendor>-<sys>-<env>``.
+
+.. code-block:: JSON
+
+  { "triple": "arm64-apple-darwin22.0.0" }
+
+uuid
+````
+
+The UUID is a string with the textual representation of the UUID of the object
+file it corresponds to. The UUID is represented as outlined in RFC 4122: with
+32 hexadecimal digits, displayed in five groups separated by hyphens, in the
+form 8-4-4-4-12 for a total of 36 characters (32 alphanumeric characters and
+four hyphens).
+
+.. code-block:: JSON
+
+  { "uuid": "2107157B-6D7E-39F6-806D-AECDC15FC533" }
+
+type
+````
+The optional ``type`` field allows you to specify the type of object file the
+JSON file represent. This is often unnecessary, and can be omitted, in which
+case the file is considered of the type ``DebugInfo``.
+
+Valid values for the ``type`` field are:
+
+* ``CoreFile``: A core file that has a checkpoint of a program's execution state.
+* ``Executable``: A normal executable.
+* ``DebugInfo``: An object file that contains only debug information.
+* ``DynamicLinker``: The platform's dynamic linker executable.
+* ``ObjectFile``: An intermediate object file.
+* ``SharedLibrary``: A shared library that can be used during execution.
+* ``StubLibrary``: A library that can be linked against but not used for execution.
+* ``JIT``: JIT code that has symbols, sections and possibly debug info.
+
+
+sections
+````````
+
+* ``name``: a string representing the section name.
+* ``type``: a string representing the section type (see below).
+* ``address``: a number representing the section file address.
+* ``size``: a number representing the section size in bytes.
+
+.. code-block:: JSON
+
+  {
+      "name": "__TEXT",
+      "type": "code",
+      "address": 0,
+      "size": 546,
+  }
+
+The ``type`` field accepts the following values: ``code``, ``container``,
+``data``, ``debug``.
+
+symbols
+```````
+
+Symbols are JSON objects with the following keys:
+
+* ``name``: a string representing the string name.
+* ``value``: a number representing the symbol value.
+* ``address``: a number representing the symbol address in a section.
+* ``size``: a number representing the symbol size.
+* ``type``: an optional string representing the symbol type (see below).
+
+A symbol must contain either a ``value`` or an ``address``. The ``type`` is
+optional.
+
+.. code-block:: JSON
+
+  {
+      "name": "foo",
+      "type": "code",
+      "size": 10,
+      "address": 4294983544,
+  }
+
+The ``type`` field accepts any type in the ``lldb::SymbolType`` enum in
+`lldb-enumerations.h <https://lldb.llvm.org/cpp_reference/lldb-enumerations_8h.html>`_
+, without the ``eSymbolType``. For example ``code`` maps to ``eSymbolTypeCode``
+and ``variableType`` to ``eSymbolTypeVariableType``.
+
+Usage
+-----
+
+Symbol files can be added with the ``target symbol add`` command. The triple
+and UUID will be used to match it to the correct module.
+
+.. code-block:: shell
+
+  (lldb) target symbol add /path/to/symbol.json
+  symbol file '/path/to/symbol.json' has been added to '/path/to/executable'
+
+You can use ``image list`` to confirm that the symbol file has been associated
+with the module.
+
+.. code-block:: shell
+
+  (lldb) image list
+  [  0] A711AB38-1FB1-38B1-B38B-859352ED2A20 0x0000000100000000 /path/to/executable
+        /path/to/symbol.json
+  [  1] 4BF76A72-53CC-3E42-8945-4E314C101535 0x00000001800c6000 /usr/lib/dyld
+
+
+Example
+-------
+
+The simplest valid JSON symbol file consists of just a triple and UUID:
+
+.. code-block:: JSON
+
+  {
+    "triple": "arm64-apple-macosx15.0.0",
+    "uuid": "A711AB38-1FB1-38B1-B38B-859352ED2A20"
+  }
+
+A JSON symbol file with symbols for ``main``, ``foo``, and ``bar``.
+
+.. code-block:: JSON
+
+  {
+      "triple": "arm64-apple-macosx15.0.0",
+      "uuid": "321C6225-2378-3E6D-B6C1-6374DEC6D81A",
+      "symbols": [
+          {
+              "name": "main",
+              "type": "code",
+              "size": 32,
+              "address": 4294983552
+          },
+          {
+              "name": "foo",
+              "type": "code",
+              "size": 8,
+              "address": 4294983544
+          },
+          {
+              "name": "bar",
+              "type": "code",
+              "size": 0,
+              "value": 255
+          }
+      ]
+  }
+
+A symbol file with a symbol ``foo`` belonging to the ``__TEXT`` section.
+
+.. code-block:: JSON
+
+  {
+      "triple": "arm64-apple-macosx15.0.0",
+      "uuid": "58489DB0-F9FF-4E62-ABD1-A7CCE5DFB879",
+      "type": "sharedlibrary",
+      "sections": [
+          {
+              "name": "__TEXT",
+              "type": "code",
+              "address": 0,
+              "size": 546
+          }
+      ],
+      "symbols": [
+          {
+              "name": "foo",
+              "address": 256,
+              "size": 17
+          }
+      ]
+  }

[medismailben]

LGTM but it would be nice if we made the optional fields stand out more by either making it bold in the paragraph or add an (optional) on the example lists.

[medismailben]

Also may be you can point to the crashlog script as an example where this is already being used.