Add a bit of documentation on the annotated disassembly output.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166639 91177308-0d34-0410-b5e6-96231b3b80d8

docs/MarkedUpDisassembly.rst

@@ -0,0 +1,88 @@
+.. _marked_up_disassembly:
+
+=======================================
+LLVM's Optional Rich Disassembly Output
+=======================================
+
+.. contents::
+   :local:
+
+Introduction
+============
+
+LLVM's default disassembly output is raw text. To allow consumers more ability
+to introspect the instructions' textual representation or to reformat for a more
+user friendly display there is an optional rich disassembly output.
+
+This optional output is sufficient to reference into individual portions of the
+instruction text. This is intended for clients like disassemblers, list file
+generators, and pretty-printers, which need more than the raw instructions and
+the ability to print them.
+
+To provide this functionality the assembly text is marked up with annotations.
+The markup is simple enough in syntax to be robust even in the case of version
+mismatches between consumers and producers. That is, the syntax generally does
+not carry semantics beyond "this text has an annotation," so consumers can
+simply ignore annotations they do not understand or do not care about.
+
+After calling ``LLVMCreateDisasm()`` to create a disassembler context the
+optional output is enable with this call:
+
+.. code-block:: c
+
+    LLVMSetDisasmOptions(DC, LLVMDisassembler_Option_UseMarkup);
+
+Then subsequent calls to ``LLVMDisasmInstruction()`` will return output strings
+with the marked up annotations.
+
+Instruction Annotations
+=======================
+
+.. _contextual markups:
+
+Contextual markups
+------------------
+
+Annoated assembly display will supply contextual markup to help clients more
+efficiently implement things like pretty printers. Most markup will be target
+independent, so clients can effectively provide good display without any target
+specific knowledge.
+
+Annotated assembly goes through the normal instruction printer, but optionally
+includes contextual tags on portions of the instruction string. An annotation
+is any '<' '>' delimited section of text(1).
+
+.. code-block:: bat
+
+    annotation: '<' tag-name tag-modifier-list ':' annotated-text '>'
+    tag-name: identifier
+    tag-modifier-list: comma delimited identifier list
+
+The tag-name is an identifier which gives the type of the annotation. For the
+first pass, this will be very simple, with memory references, registers, and
+immediates having the tag names "mem", "reg", and "imm", respectively.
+
+The tag-modifier-list is typically additional target-specific context, such as
+register class.
+
+Clients should accept and ignore any tag-names or tag-modifiers they do not
+understand, allowing the annotations to grow in richness without breaking older
+clients.
+
+For example, a possible annotation of an ARM load of a stack-relative location
+might be annotated as:
+
+.. code-block:: nasm
+
+   ldr <reg gpr:r0>, <mem regoffset:[<reg gpr:sp>, <imm:#4>]>
+
+
+1: For assembly dialects in which '<' and/or '>' are legal tokens, a literal token is escaped by following immediately with a repeat of the character.  For example, a literal '<' character is output as '<<' in an annotated assembly string.
+
+C API Details
+-------------
+
+The intended consumers of this information use the C API, therefore the new C
+API function for the disassembler will be added to provide an option to produce
+disassembled instructions with annotations, ``LLVMSetDisasmOptions()`` and the
+``LLVMDisassembler_Option_UseMarkup`` option (see above).

docs/subsystems.rst

@@ -17,6 +17,7 @@ Subsystem Documentation
    TableGenFundamentals
    DebuggingJITedCode
    GoldPlugin
+   MarkedUpDisassembly
 
 * `Writing an LLVM Pass <WritingAnLLVMPass.html>`_
     
@@ -98,3 +99,8 @@ Subsystem Documentation
    architecture.
 
 .. _`Howto: Implementing LLVM Integrated Assembler`: http://www.embecosm.com/download/ean10.html
+
+* :ref:`marked_up_disassembly`
+
+   This document describes the optional rich disassembly output syntax.
+