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