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//===- DisassemblerEmitter.cpp - Generate a disassembler ------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "DisassemblerEmitter.h"
#include "CodeGenTarget.h"
#include "Record.h"
#include "X86DisassemblerTables.h"
#include "X86RecognizableInstr.h"
using namespace llvm;
using namespace llvm::X86Disassembler;
/// DisassemblerEmitter - Contains disassembler table emitters for various
/// architectures.
/// X86 Disassembler Emitter
///
/// *** IF YOU'RE HERE TO RESOLVE A "Primary decode conflict", LOOK DOWN NEAR
/// THE END OF THIS COMMENT!
///
/// The X86 disassembler emitter is part of the X86 Disassembler, which is
/// documented in lib/Target/X86/X86Disassembler.h.
///
/// The emitter produces the tables that the disassembler uses to translate
/// instructions. The emitter generates the following tables:
///
/// - One table (CONTEXTS_SYM) that contains a mapping of attribute masks to
/// instruction contexts. Although for each attribute there are cases where
/// that attribute determines decoding, in the majority of cases decoding is
/// the same whether or not an attribute is present. For example, a 64-bit
/// instruction with an OPSIZE prefix and an XS prefix decodes the same way in
/// all cases as a 64-bit instruction with only OPSIZE set. (The XS prefix
/// may have effects on its execution, but does not change the instruction
/// returned.) This allows considerable space savings in other tables.
/// - Four tables (ONEBYTE_SYM, TWOBYTE_SYM, THREEBYTE38_SYM, and
/// THREEBYTE3A_SYM) contain the hierarchy that the decoder traverses while
/// decoding an instruction. At the lowest level of this hierarchy are
/// instruction UIDs, 16-bit integers that can be used to uniquely identify
/// the instruction and correspond exactly to its position in the list of
/// CodeGenInstructions for the target.
/// - One table (INSTRUCTIONS_SYM) contains information about the operands of
/// each instruction and how to decode them.
///
/// During table generation, there may be conflicts between instructions that
/// occupy the same space in the decode tables. These conflicts are resolved as
/// follows in setTableFields() (X86DisassemblerTables.cpp)
///
/// - If the current context is the native context for one of the instructions
/// (that is, the attributes specified for it in the LLVM tables specify
/// precisely the current context), then it has priority.
/// - If the current context isn't native for either of the instructions, then
/// the higher-priority context wins (that is, the one that is more specific).
/// That hierarchy is determined by outranks() (X86DisassemblerTables.cpp)
/// - If the current context is native for both instructions, then the table
/// emitter reports a conflict and dies.
///
/// *** RESOLUTION FOR "Primary decode conflict"S
///
/// If two instructions collide, typically the solution is (in order of
/// likelihood):
///
/// (1) to filter out one of the instructions by editing filter()
/// (X86RecognizableInstr.cpp). This is the most common resolution, but
/// check the Intel manuals first to make sure that (2) and (3) are not the
/// problem.
/// (2) to fix the tables (X86.td and its subsidiaries) so the opcodes are
/// accurate. Sometimes they are not.
/// (3) to fix the tables to reflect the actual context (for example, required
/// prefixes), and possibly to add a new context by editing
/// lib/Target/X86/X86DisassemblerDecoderCommon.h. This is unlikely to be
/// the cause.
///
/// DisassemblerEmitter.cpp contains the implementation for the emitter,
/// which simply pulls out instructions from the CodeGenTarget and pushes them
/// into X86DisassemblerTables.
/// X86DisassemblerTables.h contains the interface for the instruction tables,
/// which manage and emit the structures discussed above.
/// X86DisassemblerTables.cpp contains the implementation for the instruction
/// tables.
/// X86ModRMFilters.h contains filters that can be used to determine which
/// ModR/M values are valid for a particular instruction. These are used to
/// populate ModRMDecisions.
/// X86RecognizableInstr.h contains the interface for a single instruction,
/// which knows how to translate itself from a CodeGenInstruction and provide
/// the information necessary for integration into the tables.
/// X86RecognizableInstr.cpp contains the implementation for a single
/// instruction.
void DisassemblerEmitter::run(raw_ostream &OS) {
CodeGenTarget Target;
OS << "/*===- TableGen'erated file "
<< "---------------------------------------*- C -*-===*\n"
<< " *\n"
<< " * " << Target.getName() << " Disassembler\n"
<< " *\n"
<< " * Automatically generated file, do not edit!\n"
<< " *\n"
<< " *===---------------------------------------------------------------"
<< "-------===*/\n";
// X86 uses a custom disassembler.
if (Target.getName() == "X86") {
DisassemblerTables Tables;
std::vector<const CodeGenInstruction*> numberedInstructions;
Target.getInstructionsByEnumValue(numberedInstructions);
for (unsigned i = 0, e = numberedInstructions.size(); i != e; ++i)
RecognizableInstr::processInstr(Tables, *numberedInstructions[i], i);
// FIXME: As long as we are using exceptions, might as well drop this to the
// actual conflict site.
if (Tables.hasConflicts())
throw TGError(Target.getTargetRecord()->getLoc(),
"Primary decode conflict");
Tables.emit(OS);
return;
}
throw TGError(Target.getTargetRecord()->getLoc(),
"Unable to generate disassembler for this target");
}
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