1 //===- DisassemblerEmitter.cpp - Generate a disassembler ------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "CodeGenTarget.h"
10 #include "TableGenBackends.h"
11 #include "WebAssemblyDisassemblerEmitter.h"
12 #include "X86DisassemblerTables.h"
13 #include "X86RecognizableInstr.h"
14 #include "llvm/TableGen/Error.h"
15 #include "llvm/TableGen/Record.h"
16 #include "llvm/TableGen/TableGenBackend.h"
17 
18 using namespace llvm;
19 using namespace llvm::X86Disassembler;
20 
21 /// DisassemblerEmitter - Contains disassembler table emitters for various
22 /// architectures.
23 
24 /// X86 Disassembler Emitter
25 ///
26 /// *** IF YOU'RE HERE TO RESOLVE A "Primary decode conflict", LOOK DOWN NEAR
27 ///     THE END OF THIS COMMENT!
28 ///
29 /// The X86 disassembler emitter is part of the X86 Disassembler, which is
30 /// documented in lib/Target/X86/X86Disassembler.h.
31 ///
32 /// The emitter produces the tables that the disassembler uses to translate
33 /// instructions.  The emitter generates the following tables:
34 ///
35 /// - One table (CONTEXTS_SYM) that contains a mapping of attribute masks to
36 ///   instruction contexts.  Although for each attribute there are cases where
37 ///   that attribute determines decoding, in the majority of cases decoding is
38 ///   the same whether or not an attribute is present.  For example, a 64-bit
39 ///   instruction with an OPSIZE prefix and an XS prefix decodes the same way in
40 ///   all cases as a 64-bit instruction with only OPSIZE set.  (The XS prefix
41 ///   may have effects on its execution, but does not change the instruction
42 ///   returned.)  This allows considerable space savings in other tables.
43 /// - Six tables (ONEBYTE_SYM, TWOBYTE_SYM, THREEBYTE38_SYM, THREEBYTE3A_SYM,
44 ///   THREEBYTEA6_SYM, and THREEBYTEA7_SYM contain the hierarchy that the
45 ///   decoder traverses while decoding an instruction.  At the lowest level of
46 ///   this hierarchy are instruction UIDs, 16-bit integers that can be used to
47 ///   uniquely identify the instruction and correspond exactly to its position
48 ///   in the list of CodeGenInstructions for the target.
49 /// - One table (INSTRUCTIONS_SYM) contains information about the operands of
50 ///   each instruction and how to decode them.
51 ///
52 /// During table generation, there may be conflicts between instructions that
53 /// occupy the same space in the decode tables.  These conflicts are resolved as
54 /// follows in setTableFields() (X86DisassemblerTables.cpp)
55 ///
56 /// - If the current context is the native context for one of the instructions
57 ///   (that is, the attributes specified for it in the LLVM tables specify
58 ///   precisely the current context), then it has priority.
59 /// - If the current context isn't native for either of the instructions, then
60 ///   the higher-priority context wins (that is, the one that is more specific).
61 ///   That hierarchy is determined by outranks() (X86DisassemblerTables.cpp)
62 /// - If the current context is native for both instructions, then the table
63 ///   emitter reports a conflict and dies.
64 ///
65 /// *** RESOLUTION FOR "Primary decode conflict"S
66 ///
67 /// If two instructions collide, typically the solution is (in order of
68 /// likelihood):
69 ///
70 /// (1) to filter out one of the instructions by editing filter()
71 ///     (X86RecognizableInstr.cpp).  This is the most common resolution, but
72 ///     check the Intel manuals first to make sure that (2) and (3) are not the
73 ///     problem.
74 /// (2) to fix the tables (X86.td and its subsidiaries) so the opcodes are
75 ///     accurate.  Sometimes they are not.
76 /// (3) to fix the tables to reflect the actual context (for example, required
77 ///     prefixes), and possibly to add a new context by editing
78 ///     include/llvm/Support/X86DisassemblerDecoderCommon.h.  This is unlikely
79 ///     to be the cause.
80 ///
81 /// DisassemblerEmitter.cpp contains the implementation for the emitter,
82 ///   which simply pulls out instructions from the CodeGenTarget and pushes them
83 ///   into X86DisassemblerTables.
84 /// X86DisassemblerTables.h contains the interface for the instruction tables,
85 ///   which manage and emit the structures discussed above.
86 /// X86DisassemblerTables.cpp contains the implementation for the instruction
87 ///   tables.
88 /// X86ModRMFilters.h contains filters that can be used to determine which
89 ///   ModR/M values are valid for a particular instruction.  These are used to
90 ///   populate ModRMDecisions.
91 /// X86RecognizableInstr.h contains the interface for a single instruction,
92 ///   which knows how to translate itself from a CodeGenInstruction and provide
93 ///   the information necessary for integration into the tables.
94 /// X86RecognizableInstr.cpp contains the implementation for a single
95 ///   instruction.
96 
97 static void EmitDisassembler(RecordKeeper &Records, raw_ostream &OS) {
98   CodeGenTarget Target(Records);
99   emitSourceFileHeader(" * " + Target.getName().str() + " Disassembler", OS);
100 
101   // X86 uses a custom disassembler.
102   if (Target.getName() == "X86") {
103     DisassemblerTables Tables;
104 
105     ArrayRef<const CodeGenInstruction*> numberedInstructions =
106       Target.getInstructionsByEnumValue();
107 
108     for (unsigned i = 0, e = numberedInstructions.size(); i != e; ++i)
109       RecognizableInstr::processInstr(Tables, *numberedInstructions[i], i);
110 
111     if (Tables.hasConflicts()) {
112       PrintError(Target.getTargetRecord()->getLoc(), "Primary decode conflict");
113       return;
114     }
115 
116     Tables.emit(OS);
117     return;
118   }
119 
120   // WebAssembly has variable length opcodes, so can't use EmitFixedLenDecoder
121   // below (which depends on a Size table-gen Record), and also uses a custom
122   // disassembler.
123   if (Target.getName() == "WebAssembly") {
124     emitWebAssemblyDisassemblerTables(OS, Target.getInstructionsByEnumValue());
125     return;
126   }
127 
128   std::string PredicateNamespace = std::string(Target.getName());
129   if (PredicateNamespace == "Thumb")
130     PredicateNamespace = "ARM";
131   EmitDecoder(Records, OS, PredicateNamespace);
132 }
133 
134 static TableGen::Emitter::Opt X("gen-disassembler", EmitDisassembler,
135                                 "Generate disassembler");
136