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, AsmPrinter &AP) override;
40 };
41 }
42
43 static GCMetadataPrinterRegistry::Add<ErlangGCPrinter>
44 X("erlang", "erlang-compatible garbage collector");
45
linkErlangGCPrinter()46 void llvm::linkErlangGCPrinter() {}
47
finishAssembly(Module & M,GCModuleInfo & Info,AsmPrinter & AP)48 void ErlangGCPrinter::finishAssembly(Module &M, GCModuleInfo &Info,
49 AsmPrinter &AP) {
50 MCStreamer &OS = *AP.OutStreamer;
51 unsigned IntPtrSize = M.getDataLayout().getPointerSize();
52
53 // Put this in a custom .note section.
54 OS.SwitchSection(
55 AP.getObjFileLowering().getContext().getELFSection(".note.gc",
56 ELF::SHT_PROGBITS, 0));
57
58 // For each function...
59 for (GCModuleInfo::FuncInfoVec::iterator FI = Info.funcinfo_begin(),
60 IE = Info.funcinfo_end();
61 FI != IE; ++FI) {
62 GCFunctionInfo &MD = **FI;
63 if (MD.getStrategy().getName() != getStrategy().getName())
64 // this function is managed by some other GC
65 continue;
66 /** A compact GC layout. Emit this data structure:
67 *
68 * struct {
69 * int16_t PointCount;
70 * void *SafePointAddress[PointCount];
71 * int16_t StackFrameSize; (in words)
72 * int16_t StackArity;
73 * int16_t LiveCount;
74 * int16_t LiveOffsets[LiveCount];
75 * } __gcmap_<FUNCTIONNAME>;
76 **/
77
78 // Align to address width.
79 AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
80
81 // Emit PointCount.
82 OS.AddComment("safe point count");
83 AP.EmitInt16(MD.size());
84
85 // And each safe point...
86 for (GCFunctionInfo::iterator PI = MD.begin(), PE = MD.end(); PI != PE;
87 ++PI) {
88 // Emit the address of the safe point.
89 OS.AddComment("safe point address");
90 MCSymbol *Label = PI->Label;
91 AP.EmitLabelPlusOffset(Label /*Hi*/, 0 /*Offset*/, 4 /*Size*/);
92 }
93
94 // Stack information never change in safe points! Only print info from the
95 // first call-site.
96 GCFunctionInfo::iterator PI = MD.begin();
97
98 // Emit the stack frame size.
99 OS.AddComment("stack frame size (in words)");
100 AP.EmitInt16(MD.getFrameSize() / IntPtrSize);
101
102 // Emit stack arity, i.e. the number of stacked arguments.
103 unsigned RegisteredArgs = IntPtrSize == 4 ? 5 : 6;
104 unsigned StackArity = MD.getFunction().arg_size() > RegisteredArgs
105 ? MD.getFunction().arg_size() - RegisteredArgs
106 : 0;
107 OS.AddComment("stack arity");
108 AP.EmitInt16(StackArity);
109
110 // Emit the number of live roots in the function.
111 OS.AddComment("live root count");
112 AP.EmitInt16(MD.live_size(PI));
113
114 // And for each live root...
115 for (GCFunctionInfo::live_iterator LI = MD.live_begin(PI),
116 LE = MD.live_end(PI);
117 LI != LE; ++LI) {
118 // Emit live root's offset within the stack frame.
119 OS.AddComment("stack index (offset / wordsize)");
120 AP.EmitInt16(LI->StackOffset / IntPtrSize);
121 }
122 }
123 }
124