1 //===- lib/MC/AArch64ELFStreamer.cpp - ELF Object Output for AArch64 ------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file assembles .s files and emits AArch64 ELF .o object files. Different
11 // from generic ELF streamer in emitting mapping symbols ($x and $d) to delimit
12 // regions of data and code.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/MC/MCELFStreamer.h"
17 #include "llvm/ADT/SmallPtrSet.h"
18 #include "llvm/ADT/Twine.h"
19 #include "llvm/MC/MCAsmBackend.h"
20 #include "llvm/MC/MCAssembler.h"
21 #include "llvm/MC/MCCodeEmitter.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCELF.h"
24 #include "llvm/MC/MCELFStreamer.h"
25 #include "llvm/MC/MCELFSymbolFlags.h"
26 #include "llvm/MC/MCExpr.h"
27 #include "llvm/MC/MCInst.h"
28 #include "llvm/MC/MCObjectStreamer.h"
29 #include "llvm/MC/MCSection.h"
30 #include "llvm/MC/MCSectionELF.h"
31 #include "llvm/MC/MCStreamer.h"
32 #include "llvm/MC/MCSymbol.h"
33 #include "llvm/MC/MCValue.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/ELF.h"
36 #include "llvm/Support/ErrorHandling.h"
37 #include "llvm/Support/raw_ostream.h"
43 /// Extend the generic ELFStreamer class so that it can emit mapping symbols at
44 /// the appropriate points in the object files. These symbols are defined in the
46 /// infocenter.arm.com/help/topic/com.arm.doc.ihi0056a/IHI0056A_aaelf64.pdf
48 /// In brief: $x or $d should be emitted at the start of each contiguous region
49 /// of A64 code or data in a section. In practice, this emission does not rely
50 /// on explicit assembler directives but on inherent properties of the
51 /// directives doing the emission (e.g. ".byte" is data, "add x0, x0, x0" an
54 /// As a result this system is orthogonal to the DataRegion infrastructure used
56 class AArch64ELFStreamer : public MCELFStreamer {
58 AArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB, raw_ostream &OS,
59 MCCodeEmitter *Emitter)
60 : MCELFStreamer(Context, TAB, OS, Emitter), MappingSymbolCounter(0),
63 ~AArch64ELFStreamer() {}
65 virtual void ChangeSection(const MCSection *Section,
66 const MCExpr *Subsection) {
67 // We have to keep track of the mapping symbol state of any sections we
68 // use. Each one should start off as EMS_None, which is provided as the
69 // default constructor by DenseMap::lookup.
70 LastMappingSymbols[getPreviousSection().first] = LastEMS;
71 LastEMS = LastMappingSymbols.lookup(Section);
73 MCELFStreamer::ChangeSection(Section, Subsection);
76 /// This function is the one used to emit instruction data into the ELF
77 /// streamer. We override it to add the appropriate mapping symbol if
79 virtual void EmitInstruction(const MCInst& Inst, const MCSubtargetInfo &STI) {
80 EmitA64MappingSymbol();
81 MCELFStreamer::EmitInstruction(Inst, STI);
84 /// This is one of the functions used to emit data into an ELF section, so the
85 /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
87 virtual void EmitBytes(StringRef Data) {
88 EmitDataMappingSymbol();
89 MCELFStreamer::EmitBytes(Data);
92 /// This is one of the functions used to emit data into an ELF section, so the
93 /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
95 virtual void EmitValueImpl(const MCExpr *Value, unsigned Size,
97 EmitDataMappingSymbol();
98 MCELFStreamer::EmitValueImpl(Value, Size, Loc);
102 enum ElfMappingSymbol {
108 void EmitDataMappingSymbol() {
109 if (LastEMS == EMS_Data) return;
110 EmitMappingSymbol("$d");
114 void EmitA64MappingSymbol() {
115 if (LastEMS == EMS_A64) return;
116 EmitMappingSymbol("$x");
120 void EmitMappingSymbol(StringRef Name) {
121 MCSymbol *Start = getContext().CreateTempSymbol();
125 getContext().GetOrCreateSymbol(Name + "." +
126 Twine(MappingSymbolCounter++));
128 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
129 MCELF::SetType(SD, ELF::STT_NOTYPE);
130 MCELF::SetBinding(SD, ELF::STB_LOCAL);
131 SD.setExternal(false);
132 AssignSection(Symbol, getCurrentSection().first);
134 const MCExpr *Value = MCSymbolRefExpr::Create(Start, getContext());
135 Symbol->setVariableValue(Value);
138 int64_t MappingSymbolCounter;
140 DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
141 ElfMappingSymbol LastEMS;
148 MCELFStreamer* createAArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
149 raw_ostream &OS, MCCodeEmitter *Emitter,
150 bool RelaxAll, bool NoExecStack) {
151 AArch64ELFStreamer *S = new AArch64ELFStreamer(Context, TAB, OS, Emitter);
153 S->getAssembler().setRelaxAll(true);
155 S->getAssembler().setNoExecStack(true);