llvm/llvm/lib/Target/PowerPC/MCTargetDesc/PPCELFStreamer.cpp

//===-------- PPCELFStreamer.cpp - ELF Object Output ---------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This is a custom MCELFStreamer for PowerPC.
//
// The purpose of the custom ELF streamer is to allow us to intercept
// instructions as they are being emitted and align all 8 byte instructions
// to a 64 byte boundary if required (by adding a 4 byte nop). This is important
// because 8 byte instructions are not allowed to cross 64 byte boundaries
// and by aliging anything that is within 4 bytes of the boundary we can
// guarantee that the 8 byte instructions do not cross that boundary.
//
//===----------------------------------------------------------------------===//

#include "PPCELFStreamer.h"
#include "PPCFixupKinds.h"
#include "PPCMCCodeEmitter.h"
#include "PPCMCTargetDesc.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSymbolELF.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/SourceMgr.h"

usingnamespacellvm;

PPCELFStreamer::PPCELFStreamer(MCContext &Context,
                               std::unique_ptr<MCAsmBackend> MAB,
                               std::unique_ptr<MCObjectWriter> OW,
                               std::unique_ptr<MCCodeEmitter> Emitter)
    : … { … }

void PPCELFStreamer::emitPrefixedInstruction(const MCInst &Inst,
                                             const MCSubtargetInfo &STI) { … }

void PPCELFStreamer::emitInstruction(const MCInst &Inst,
                                     const MCSubtargetInfo &STI) { … }

void PPCELFStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) { … }

// This linker time GOT PC Relative optimization relocation will look like this:
//   pld <reg> symbol@got@pcrel
// <Label###>:
//   .reloc Label###-8,R_PPC64_PCREL_OPT,.-(Label###-8)
//   load <loadedreg>, 0(<reg>)
// The reason we place the label after the PLDpc instruction is that there
// may be an alignment nop before it since prefixed instructions must not
// cross a 64-byte boundary (please see
// PPCELFStreamer::emitPrefixedInstruction()). When referring to the
// label, we subtract the width of a prefixed instruction (8 bytes) to ensure
// we refer to the PLDpc.
void PPCELFStreamer::emitGOTToPCRelReloc(const MCInst &Inst) { … }

// Emit the label that immediately follows the PLDpc for a link time GOT PC Rel
// optimization.
void PPCELFStreamer::emitGOTToPCRelLabel(const MCInst &Inst) { … }

// This function checks if the parameter Inst is part of the setup for a link
// time GOT PC Relative optimization. For example in this situation:
// <MCInst PLDpc <MCOperand Reg:282> <MCOperand Expr:(glob_double@got@pcrel)>
//   <MCOperand Imm:0> <MCOperand Expr:(.Lpcrel@<<invalid>>)>>
// <MCInst SOME_LOAD <MCOperand Reg:22> <MCOperand Imm:0> <MCOperand Reg:282>
//   <MCOperand Expr:(.Lpcrel@<<invalid>>)>>
// The above is a pair of such instructions and this function will not return
// std::nullopt for either one of them. In both cases we are looking for the
// last operand <MCOperand Expr:(.Lpcrel@<<invalid>>)> which needs to be an
// MCExpr and has the flag MCSymbolRefExpr::VK_PPC_PCREL_OPT. After that we just
// look at the opcode and in the case of PLDpc we will return true. For the load
// (or store) this function will return false indicating it has found the second
// instruciton in the pair.
std::optional<bool> llvm::isPartOfGOTToPCRelPair(const MCInst &Inst,
                                                 const MCSubtargetInfo &STI) { … }

MCELFStreamer *llvm::createPPCELFStreamer(
    MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
    std::unique_ptr<MCObjectWriter> OW,
    std::unique_ptr<MCCodeEmitter> Emitter) { … }