1 //===-- ErlangGCPrinter.cpp - Erlang/OTP frametable emitter -----*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the compiler plugin that is used in order to emit
11 // garbage collection information in a convenient layout for parsing and
12 // loading in the Erlang/OTP runtime.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #include "llvm/CodeGen/AsmPrinter.h"
17 #include "llvm/CodeGen/GCMetadataPrinter.h"
18 #include "llvm/CodeGen/GCs.h"
19 #include "llvm/IR/DataLayout.h"
20 #include "llvm/IR/Function.h"
21 #include "llvm/IR/Instruction.h"
22 #include "llvm/IR/IntrinsicInst.h"
23 #include "llvm/IR/Metadata.h"
24 #include "llvm/MC/MCAsmInfo.h"
25 #include "llvm/MC/MCContext.h"
26 #include "llvm/MC/MCSectionELF.h"
27 #include "llvm/MC/MCStreamer.h"
28 #include "llvm/MC/MCSymbol.h"
29 #include "llvm/Target/TargetLoweringObjectFile.h"
30 #include "llvm/Target/TargetMachine.h"
31 #include "llvm/Target/TargetSubtargetInfo.h"
32
33 using namespace llvm;
34
35 namespace {
36
37 class ErlangGCPrinter : public GCMetadataPrinter {
38 public:
39 void finishAssembly(Module &M, GCModuleInfo &Info,
40 AsmPrinter &AP) override;
41 };
42
43 }
44
45 static GCMetadataPrinterRegistry::Add<ErlangGCPrinter>
46 X("erlang", "erlang-compatible garbage collector");
47
linkErlangGCPrinter()48 void llvm::linkErlangGCPrinter() { }
49
finishAssembly(Module & M,GCModuleInfo & Info,AsmPrinter & AP)50 void ErlangGCPrinter::finishAssembly(Module &M, GCModuleInfo &Info,
51 AsmPrinter &AP) {
52 MCStreamer &OS = AP.OutStreamer;
53 unsigned IntPtrSize =
54 AP.TM.getSubtargetImpl()->getDataLayout()->getPointerSize();
55
56 // Put this in a custom .note section.
57 AP.OutStreamer.SwitchSection(AP.getObjFileLowering().getContext()
58 .getELFSection(".note.gc", ELF::SHT_PROGBITS, 0,
59 SectionKind::getDataRel()));
60
61 // For each function...
62 for (GCModuleInfo::FuncInfoVec::iterator FI = Info.funcinfo_begin(),
63 IE = Info.funcinfo_end();
64 FI != IE; ++FI) {
65 GCFunctionInfo &MD = **FI;
66 if (MD.getStrategy().getName() != getStrategy().getName())
67 // this function is managed by some other GC
68 continue;
69 /** A compact GC layout. Emit this data structure:
70 *
71 * struct {
72 * int16_t PointCount;
73 * void *SafePointAddress[PointCount];
74 * int16_t StackFrameSize; (in words)
75 * int16_t StackArity;
76 * int16_t LiveCount;
77 * int16_t LiveOffsets[LiveCount];
78 * } __gcmap_<FUNCTIONNAME>;
79 **/
80
81 // Align to address width.
82 AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
83
84 // Emit PointCount.
85 OS.AddComment("safe point count");
86 AP.EmitInt16(MD.size());
87
88 // And each safe point...
89 for (GCFunctionInfo::iterator PI = MD.begin(), PE = MD.end(); PI != PE;
90 ++PI) {
91 // Emit the address of the safe point.
92 OS.AddComment("safe point address");
93 MCSymbol *Label = PI->Label;
94 AP.EmitLabelPlusOffset(Label/*Hi*/, 0/*Offset*/, 4/*Size*/);
95 }
96
97 // Stack information never change in safe points! Only print info from the
98 // first call-site.
99 GCFunctionInfo::iterator PI = MD.begin();
100
101 // Emit the stack frame size.
102 OS.AddComment("stack frame size (in words)");
103 AP.EmitInt16(MD.getFrameSize() / IntPtrSize);
104
105 // Emit stack arity, i.e. the number of stacked arguments.
106 unsigned RegisteredArgs = IntPtrSize == 4 ? 5 : 6;
107 unsigned StackArity = MD.getFunction().arg_size() > RegisteredArgs ?
108 MD.getFunction().arg_size() - RegisteredArgs : 0;
109 OS.AddComment("stack arity");
110 AP.EmitInt16(StackArity);
111
112 // Emit the number of live roots in the function.
113 OS.AddComment("live root count");
114 AP.EmitInt16(MD.live_size(PI));
115
116 // And for each live root...
117 for (GCFunctionInfo::live_iterator LI = MD.live_begin(PI),
118 LE = MD.live_end(PI);
119 LI != LE; ++LI) {
120 // Emit live root's offset within the stack frame.
121 OS.AddComment("stack index (offset / wordsize)");
122 AP.EmitInt16(LI->StackOffset / IntPtrSize);
123 }
124 }
125 }
126