1 ======================================= 2 LLVM's Optional Rich Disassembly Output 3 ======================================= 4 5 .. contents:: 6 :local: 7 8 Introduction 9 ============ 10 11 LLVM's default disassembly output is raw text. To allow consumers more ability 12 to introspect the instructions' textual representation or to reformat for a more 13 user friendly display there is an optional rich disassembly output. 14 15 This optional output is sufficient to reference into individual portions of the 16 instruction text. This is intended for clients like disassemblers, list file 17 generators, and pretty-printers, which need more than the raw instructions and 18 the ability to print them. 19 20 To provide this functionality the assembly text is marked up with annotations. 21 The markup is simple enough in syntax to be robust even in the case of version 22 mismatches between consumers and producers. That is, the syntax generally does 23 not carry semantics beyond "this text has an annotation," so consumers can 24 simply ignore annotations they do not understand or do not care about. 25 26 After calling ``LLVMCreateDisasm()`` to create a disassembler context the 27 optional output is enable with this call: 28 29 .. code-block:: c 30 31 LLVMSetDisasmOptions(DC, LLVMDisassembler_Option_UseMarkup); 32 33 Then subsequent calls to ``LLVMDisasmInstruction()`` will return output strings 34 with the marked up annotations. 35 36 Instruction Annotations 37 ======================= 38 39 .. _contextual markups: 40 41 Contextual markups 42 ------------------ 43 44 Annoated assembly display will supply contextual markup to help clients more 45 efficiently implement things like pretty printers. Most markup will be target 46 independent, so clients can effectively provide good display without any target 47 specific knowledge. 48 49 Annotated assembly goes through the normal instruction printer, but optionally 50 includes contextual tags on portions of the instruction string. An annotation 51 is any '<' '>' delimited section of text(1). 52 53 .. code-block:: bat 54 55 annotation: '<' tag-name tag-modifier-list ':' annotated-text '>' 56 tag-name: identifier 57 tag-modifier-list: comma delimited identifier list 58 59 The tag-name is an identifier which gives the type of the annotation. For the 60 first pass, this will be very simple, with memory references, registers, and 61 immediates having the tag names "mem", "reg", and "imm", respectively. 62 63 The tag-modifier-list is typically additional target-specific context, such as 64 register class. 65 66 Clients should accept and ignore any tag-names or tag-modifiers they do not 67 understand, allowing the annotations to grow in richness without breaking older 68 clients. 69 70 For example, a possible annotation of an ARM load of a stack-relative location 71 might be annotated as: 72 73 .. code-block:: nasm 74 75 ldr <reg gpr:r0>, <mem regoffset:[<reg gpr:sp>, <imm:#4>]> 76 77 78 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. 79 80 C API Details 81 ------------- 82 83 The intended consumers of this information use the C API, therefore the new C 84 API function for the disassembler will be added to provide an option to produce 85 disassembled instructions with annotations, ``LLVMSetDisasmOptions()`` and the 86 ``LLVMDisassembler_Option_UseMarkup`` option (see above). 87
