LLVM 19.0.0git
PPCELFStreamer.cpp
Go to the documentation of this file.
1//===-------- PPCELFStreamer.cpp - ELF Object Output ---------------------===//
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// This is a custom MCELFStreamer for PowerPC.
10//
11// The purpose of the custom ELF streamer is to allow us to intercept
12// instructions as they are being emitted and align all 8 byte instructions
13// to a 64 byte boundary if required (by adding a 4 byte nop). This is important
14// because 8 byte instructions are not allowed to cross 64 byte boundaries
15// and by aliging anything that is within 4 bytes of the boundary we can
16// guarantee that the 8 byte instructions do not cross that boundary.
17//
18//===----------------------------------------------------------------------===//
19
20#include "PPCELFStreamer.h"
21#include "PPCFixupKinds.h"
22#include "PPCMCCodeEmitter.h"
23#include "PPCMCTargetDesc.h"
26#include "llvm/MC/MCAssembler.h"
28#include "llvm/MC/MCContext.h"
29#include "llvm/MC/MCInst.h"
30#include "llvm/MC/MCInstrDesc.h"
32#include "llvm/MC/MCSymbolELF.h"
35
36using namespace llvm;
37
39 std::unique_ptr<MCAsmBackend> MAB,
40 std::unique_ptr<MCObjectWriter> OW,
41 std::unique_ptr<MCCodeEmitter> Emitter)
42 : MCELFStreamer(Context, std::move(MAB), std::move(OW), std::move(Emitter)),
43 LastLabel(nullptr) {}
44
45void PPCELFStreamer::emitPrefixedInstruction(const MCInst &Inst,
46 const MCSubtargetInfo &STI) {
47 // Prefixed instructions must not cross a 64-byte boundary (i.e. prefix is
48 // before the boundary and the remaining 4-bytes are after the boundary). In
49 // order to achieve this, a nop is added prior to any such boundary-crossing
50 // prefixed instruction. Align to 64 bytes if possible but add a maximum of 4
51 // bytes when trying to do that. If alignment requires adding more than 4
52 // bytes then the instruction won't be aligned. When emitting a code alignment
53 // a new fragment is created for this alignment. This fragment will contain
54 // all of the nops required as part of the alignment operation. In the cases
55 // when no nops are added then The fragment is still created but it remains
56 // empty.
57 emitCodeAlignment(Align(64), &STI, 4);
58
59 // Emit the instruction.
60 // Since the previous emit created a new fragment then adding this instruction
61 // also forces the addition of a new fragment. Inst is now the first
62 // instruction in that new fragment.
64
65 // The above instruction is forced to start a new fragment because it
66 // comes after a code alignment fragment. Get that new fragment.
67 MCFragment *InstructionFragment = getCurrentFragment();
68 SMLoc InstLoc = Inst.getLoc();
69 // Check if there was a last label emitted.
70 if (LastLabel && !LastLabel->isUnset() && LastLabelLoc.isValid() &&
71 InstLoc.isValid()) {
72 const SourceMgr *SourceManager = getContext().getSourceManager();
73 unsigned InstLine = SourceManager->FindLineNumber(InstLoc);
74 unsigned LabelLine = SourceManager->FindLineNumber(LastLabelLoc);
75 // If the Label and the Instruction are on the same line then move the
76 // label to the top of the fragment containing the aligned instruction that
77 // was just added.
78 if (InstLine == LabelLine) {
79 assignFragment(LastLabel, InstructionFragment);
80 LastLabel->setOffset(0);
81 }
82 }
83}
84
86 const MCSubtargetInfo &STI) {
89
90 // If the instruction is a part of the GOT to PC-Rel link time optimization
91 // instruction pair, return a value, otherwise return std::nullopt. A true
92 // returned value means the instruction is the PLDpc and a false value means
93 // it is the user instruction.
94 std::optional<bool> IsPartOfGOTToPCRelPair =
95 isPartOfGOTToPCRelPair(Inst, STI);
96
97 // User of the GOT-indirect address.
98 // For example, the load that will get the relocation as follows:
99 // .reloc .Lpcrel1-8,R_PPC64_PCREL_OPT,.-(.Lpcrel1-8)
100 // lwa 3, 4(3)
101 if (IsPartOfGOTToPCRelPair && !*IsPartOfGOTToPCRelPair)
102 emitGOTToPCRelReloc(Inst);
103
104 // Special handling is only for prefixed instructions.
105 if (!Emitter->isPrefixedInstruction(Inst)) {
107 return;
108 }
109 emitPrefixedInstruction(Inst, STI);
110
111 // Producer of the GOT-indirect address.
112 // For example, the prefixed load from the got that will get the label as
113 // follows:
114 // pld 3, vec@got@pcrel(0), 1
115 // .Lpcrel1:
116 if (IsPartOfGOTToPCRelPair && *IsPartOfGOTToPCRelPair)
117 emitGOTToPCRelLabel(Inst);
118}
119
121 LastLabel = Symbol;
122 LastLabelLoc = Loc;
124}
125
126// This linker time GOT PC Relative optimization relocation will look like this:
127// pld <reg> symbol@got@pcrel
128// <Label###>:
129// .reloc Label###-8,R_PPC64_PCREL_OPT,.-(Label###-8)
130// load <loadedreg>, 0(<reg>)
131// The reason we place the label after the PLDpc instruction is that there
132// may be an alignment nop before it since prefixed instructions must not
133// cross a 64-byte boundary (please see
134// PPCELFStreamer::emitPrefixedInstruction()). When referring to the
135// label, we subtract the width of a prefixed instruction (8 bytes) to ensure
136// we refer to the PLDpc.
137void PPCELFStreamer::emitGOTToPCRelReloc(const MCInst &Inst) {
138 // Get the last operand which contains the symbol.
139 const MCOperand &Operand = Inst.getOperand(Inst.getNumOperands() - 1);
140 assert(Operand.isExpr() && "Expecting an MCExpr.");
141 // Cast the last operand to MCSymbolRefExpr to get the symbol.
142 const MCExpr *Expr = Operand.getExpr();
143 const MCSymbolRefExpr *SymExpr = static_cast<const MCSymbolRefExpr *>(Expr);
145 "Expecting a symbol of type VK_PPC_PCREL_OPT");
146 MCSymbol *LabelSym =
148 const MCExpr *LabelExpr = MCSymbolRefExpr::create(LabelSym, getContext());
149 const MCExpr *Eight = MCConstantExpr::create(8, getContext());
150 // SubExpr is just Label###-8
151 const MCExpr *SubExpr =
152 MCBinaryExpr::createSub(LabelExpr, Eight, getContext());
153 MCSymbol *CurrentLocation = getContext().createTempSymbol();
154 const MCExpr *CurrentLocationExpr =
155 MCSymbolRefExpr::create(CurrentLocation, getContext());
156 // SubExpr2 is .-(Label###-8)
157 const MCExpr *SubExpr2 =
158 MCBinaryExpr::createSub(CurrentLocationExpr, SubExpr, getContext());
159
160 MCDataFragment *DF = static_cast<MCDataFragment *>(LabelSym->getFragment());
161 assert(DF && "Expecting a valid data fragment.");
162 MCFixupKind FixupKind = static_cast<MCFixupKind>(FirstLiteralRelocationKind +
163 ELF::R_PPC64_PCREL_OPT);
164 DF->getFixups().push_back(
165 MCFixup::create(LabelSym->getOffset() - 8, SubExpr2,
166 FixupKind, Inst.getLoc()));
167 emitLabel(CurrentLocation, Inst.getLoc());
168}
169
170// Emit the label that immediately follows the PLDpc for a link time GOT PC Rel
171// optimization.
172void PPCELFStreamer::emitGOTToPCRelLabel(const MCInst &Inst) {
173 // Get the last operand which contains the symbol.
174 const MCOperand &Operand = Inst.getOperand(Inst.getNumOperands() - 1);
175 assert(Operand.isExpr() && "Expecting an MCExpr.");
176 // Cast the last operand to MCSymbolRefExpr to get the symbol.
177 const MCExpr *Expr = Operand.getExpr();
178 const MCSymbolRefExpr *SymExpr = static_cast<const MCSymbolRefExpr *>(Expr);
180 "Expecting a symbol of type VK_PPC_PCREL_OPT");
181 MCSymbol *LabelSym =
183 emitLabel(LabelSym, Inst.getLoc());
184}
185
186// This function checks if the parameter Inst is part of the setup for a link
187// time GOT PC Relative optimization. For example in this situation:
188// <MCInst PLDpc <MCOperand Reg:282> <MCOperand Expr:(glob_double@got@pcrel)>
189// <MCOperand Imm:0> <MCOperand Expr:(.Lpcrel@<<invalid>>)>>
190// <MCInst SOME_LOAD <MCOperand Reg:22> <MCOperand Imm:0> <MCOperand Reg:282>
191// <MCOperand Expr:(.Lpcrel@<<invalid>>)>>
192// The above is a pair of such instructions and this function will not return
193// std::nullopt for either one of them. In both cases we are looking for the
194// last operand <MCOperand Expr:(.Lpcrel@<<invalid>>)> which needs to be an
195// MCExpr and has the flag MCSymbolRefExpr::VK_PPC_PCREL_OPT. After that we just
196// look at the opcode and in the case of PLDpc we will return true. For the load
197// (or store) this function will return false indicating it has found the second
198// instruciton in the pair.
199std::optional<bool> llvm::isPartOfGOTToPCRelPair(const MCInst &Inst,
200 const MCSubtargetInfo &STI) {
201 // Need at least two operands.
202 if (Inst.getNumOperands() < 2)
203 return std::nullopt;
204
205 unsigned LastOp = Inst.getNumOperands() - 1;
206 // The last operand needs to be an MCExpr and it needs to have a variant kind
207 // of VK_PPC_PCREL_OPT. If it does not satisfy these conditions it is not a
208 // link time GOT PC Rel opt instruction and we can ignore it and return
209 // std::nullopt.
210 const MCOperand &Operand = Inst.getOperand(LastOp);
211 if (!Operand.isExpr())
212 return std::nullopt;
213
214 // Check for the variant kind VK_PPC_PCREL_OPT in this expression.
215 const MCExpr *Expr = Operand.getExpr();
216 const MCSymbolRefExpr *SymExpr = static_cast<const MCSymbolRefExpr *>(Expr);
217 if (!SymExpr || SymExpr->getKind() != MCSymbolRefExpr::VK_PPC_PCREL_OPT)
218 return std::nullopt;
219
220 return (Inst.getOpcode() == PPC::PLDpc);
221}
222
224 MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
225 std::unique_ptr<MCObjectWriter> OW,
226 std::unique_ptr<MCCodeEmitter> Emitter) {
227 return new PPCELFStreamer(Context, std::move(MAB), std::move(OW),
228 std::move(Emitter));
229}
dxil DXContainer Global Emitter
static RegisterPass< DebugifyFunctionPass > DF("debugify-function", "Attach debug info to a function")
LLVMContext & Context
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
MCCodeEmitter * getEmitterPtr() const
Definition: MCAssembler.h:330
static const MCBinaryExpr * createSub(const MCExpr *LHS, const MCExpr *RHS, MCContext &Ctx)
Definition: MCExpr.h:621
static const MCConstantExpr * create(int64_t Value, MCContext &Ctx, bool PrintInHex=false, unsigned SizeInBytes=0)
Definition: MCExpr.cpp:194
Context object for machine code objects.
Definition: MCContext.h:81
MCSymbol * createTempSymbol()
Create a temporary symbol with a unique name.
Definition: MCContext.cpp:322
const SourceMgr * getSourceManager() const
Definition: MCContext.h:426
MCSymbol * getOrCreateSymbol(const Twine &Name)
Lookup the symbol inside with the specified Name.
Definition: MCContext.cpp:201
Fragment for data and encoded instructions.
Definition: MCFragment.h:242
void emitLabel(MCSymbol *Symbol, SMLoc Loc=SMLoc()) override
Emit a label for Symbol into the current section.
Base class for the full range of assembler expressions which are needed for parsing.
Definition: MCExpr.h:35
static MCFixup create(uint32_t Offset, const MCExpr *Value, MCFixupKind Kind, SMLoc Loc=SMLoc())
Definition: MCFixup.h:87
Instances of this class represent a single low-level machine instruction.
Definition: MCInst.h:184
unsigned getNumOperands() const
Definition: MCInst.h:208
SMLoc getLoc() const
Definition: MCInst.h:204
unsigned getOpcode() const
Definition: MCInst.h:198
const MCOperand & getOperand(unsigned i) const
Definition: MCInst.h:206
MCAssembler & getAssembler()
void emitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI) override
Emit the given Instruction into the current section.
MCFragment * getCurrentFragment() const
void emitCodeAlignment(Align ByteAlignment, const MCSubtargetInfo *STI, unsigned MaxBytesToEmit=0) override
Emit nops until the byte alignment ByteAlignment is reached.
Instances of this class represent operands of the MCInst class.
Definition: MCInst.h:36
const MCExpr * getExpr() const
Definition: MCInst.h:114
bool isExpr() const
Definition: MCInst.h:65
void assignFragment(MCSymbol *Symbol, MCFragment *Fragment)
Sets the symbol's section.
Definition: MCStreamer.cpp:415
MCContext & getContext() const
Definition: MCStreamer.h:297
Generic base class for all target subtargets.
Represent a reference to a symbol from inside an expression.
Definition: MCExpr.h:192
const MCSymbol & getSymbol() const
Definition: MCExpr.h:410
static const MCSymbolRefExpr * create(const MCSymbol *Symbol, MCContext &Ctx)
Definition: MCExpr.h:397
VariantKind getKind() const
Definition: MCExpr.h:412
MCSymbol - Instances of this class represent a symbol name in the MC file, and MCSymbols are created ...
Definition: MCSymbol.h:40
StringRef getName() const
getName - Get the symbol name.
Definition: MCSymbol.h:205
void setOffset(uint64_t Value)
Definition: MCSymbol.h:333
bool isUnset() const
Definition: MCSymbol.h:325
uint64_t getOffset() const
Definition: MCSymbol.h:327
MCFragment * getFragment(bool SetUsed=true) const
Definition: MCSymbol.h:397
void emitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI) override
Emit the given Instruction into the current section.
PPCELFStreamer(MCContext &Context, std::unique_ptr< MCAsmBackend > MAB, std::unique_ptr< MCObjectWriter > OW, std::unique_ptr< MCCodeEmitter > Emitter)
void emitLabel(MCSymbol *Symbol, SMLoc Loc=SMLoc()) override
Emit a label for Symbol into the current section.
Represents a location in source code.
Definition: SMLoc.h:23
constexpr bool isValid() const
Definition: SMLoc.h:29
This owns the files read by a parser, handles include stacks, and handles diagnostic wrangling.
Definition: SourceMgr.h:31
unsigned FindLineNumber(SMLoc Loc, unsigned BufferID=0) const
Find the line number for the specified location in the specified file.
Definition: SourceMgr.h:196
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
MCFixupKind
Extensible enumeration to represent the type of a fixup.
Definition: MCFixup.h:21
@ FirstLiteralRelocationKind
The range [FirstLiteralRelocationKind, MaxTargetFixupKind) is used for relocations coming from ....
Definition: MCFixup.h:50
OutputIt move(R &&Range, OutputIt Out)
Provide wrappers to std::move which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1849
MCELFStreamer * createPPCELFStreamer(MCContext &Context, std::unique_ptr< MCAsmBackend > MAB, std::unique_ptr< MCObjectWriter > OW, std::unique_ptr< MCCodeEmitter > Emitter)
std::optional< bool > isPartOfGOTToPCRelPair(const MCInst &Inst, const MCSubtargetInfo &STI)
Implement std::hash so that hash_code can be used in STL containers.
Definition: BitVector.h:858
This struct is a compact representation of a valid (non-zero power of two) alignment.
Definition: Alignment.h:39