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