1 //===-- OcamlGCPrinter.cpp - Ocaml frametable emitter ---------------------===//
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 printing the assembly code for an Ocaml frametable.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/CodeGen/GCs.h"
15 #include "llvm/ADT/SmallString.h"
16 #include "llvm/CodeGen/AsmPrinter.h"
17 #include "llvm/CodeGen/GCMetadataPrinter.h"
18 #include "llvm/IR/DataLayout.h"
19 #include "llvm/IR/Mangler.h"
20 #include "llvm/IR/Module.h"
21 #include "llvm/MC/MCAsmInfo.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCStreamer.h"
24 #include "llvm/MC/MCSymbol.h"
25 #include "llvm/Support/ErrorHandling.h"
26 #include "llvm/Support/FormattedStream.h"
27 #include "llvm/Target/TargetLoweringObjectFile.h"
28 #include "llvm/Target/TargetMachine.h"
29 #include "llvm/Target/TargetSubtargetInfo.h"
30 #include <cctype>
31 using namespace llvm;
32 
33 namespace {
34 
35 class OcamlGCMetadataPrinter : public GCMetadataPrinter {
36 public:
37   void beginAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
38   void finishAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
39 };
40 }
41 
42 static GCMetadataPrinterRegistry::Add<OcamlGCMetadataPrinter>
43     Y("ocaml", "ocaml 3.10-compatible collector");
44 
linkOcamlGCPrinter()45 void llvm::linkOcamlGCPrinter() {}
46 
EmitCamlGlobal(const Module & M,AsmPrinter & AP,const char * Id)47 static void EmitCamlGlobal(const Module &M, AsmPrinter &AP, const char *Id) {
48   const std::string &MId = M.getModuleIdentifier();
49 
50   std::string SymName;
51   SymName += "caml";
52   size_t Letter = SymName.size();
53   SymName.append(MId.begin(), std::find(MId.begin(), MId.end(), '.'));
54   SymName += "__";
55   SymName += Id;
56 
57   // Capitalize the first letter of the module name.
58   SymName[Letter] = toupper(SymName[Letter]);
59 
60   SmallString<128> TmpStr;
61   Mangler::getNameWithPrefix(TmpStr, SymName, M.getDataLayout());
62 
63   MCSymbol *Sym = AP.OutContext.getOrCreateSymbol(TmpStr);
64 
65   AP.OutStreamer->EmitSymbolAttribute(Sym, MCSA_Global);
66   AP.OutStreamer->EmitLabel(Sym);
67 }
68 
beginAssembly(Module & M,GCModuleInfo & Info,AsmPrinter & AP)69 void OcamlGCMetadataPrinter::beginAssembly(Module &M, GCModuleInfo &Info,
70                                            AsmPrinter &AP) {
71   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getTextSection());
72   EmitCamlGlobal(M, AP, "code_begin");
73 
74   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getDataSection());
75   EmitCamlGlobal(M, AP, "data_begin");
76 }
77 
78 /// emitAssembly - Print the frametable. The ocaml frametable format is thus:
79 ///
80 ///   extern "C" struct align(sizeof(intptr_t)) {
81 ///     uint16_t NumDescriptors;
82 ///     struct align(sizeof(intptr_t)) {
83 ///       void *ReturnAddress;
84 ///       uint16_t FrameSize;
85 ///       uint16_t NumLiveOffsets;
86 ///       uint16_t LiveOffsets[NumLiveOffsets];
87 ///     } Descriptors[NumDescriptors];
88 ///   } caml${module}__frametable;
89 ///
90 /// Note that this precludes programs from stack frames larger than 64K
91 /// (FrameSize and LiveOffsets would overflow). FrameTablePrinter will abort if
92 /// either condition is detected in a function which uses the GC.
93 ///
finishAssembly(Module & M,GCModuleInfo & Info,AsmPrinter & AP)94 void OcamlGCMetadataPrinter::finishAssembly(Module &M, GCModuleInfo &Info,
95                                             AsmPrinter &AP) {
96   unsigned IntPtrSize = M.getDataLayout().getPointerSize();
97 
98   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getTextSection());
99   EmitCamlGlobal(M, AP, "code_end");
100 
101   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getDataSection());
102   EmitCamlGlobal(M, AP, "data_end");
103 
104   // FIXME: Why does ocaml emit this??
105   AP.OutStreamer->EmitIntValue(0, IntPtrSize);
106 
107   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getDataSection());
108   EmitCamlGlobal(M, AP, "frametable");
109 
110   int NumDescriptors = 0;
111   for (GCModuleInfo::FuncInfoVec::iterator I = Info.funcinfo_begin(),
112                                            IE = Info.funcinfo_end();
113        I != IE; ++I) {
114     GCFunctionInfo &FI = **I;
115     if (FI.getStrategy().getName() != getStrategy().getName())
116       // this function is managed by some other GC
117       continue;
118     for (GCFunctionInfo::iterator J = FI.begin(), JE = FI.end(); J != JE; ++J) {
119       NumDescriptors++;
120     }
121   }
122 
123   if (NumDescriptors >= 1 << 16) {
124     // Very rude!
125     report_fatal_error(" Too much descriptor for ocaml GC");
126   }
127   AP.EmitInt16(NumDescriptors);
128   AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
129 
130   for (GCModuleInfo::FuncInfoVec::iterator I = Info.funcinfo_begin(),
131                                            IE = Info.funcinfo_end();
132        I != IE; ++I) {
133     GCFunctionInfo &FI = **I;
134     if (FI.getStrategy().getName() != getStrategy().getName())
135       // this function is managed by some other GC
136       continue;
137 
138     uint64_t FrameSize = FI.getFrameSize();
139     if (FrameSize >= 1 << 16) {
140       // Very rude!
141       report_fatal_error("Function '" + FI.getFunction().getName() +
142                          "' is too large for the ocaml GC! "
143                          "Frame size " +
144                          Twine(FrameSize) + ">= 65536.\n"
145                                             "(" +
146                          Twine(uintptr_t(&FI)) + ")");
147     }
148 
149     AP.OutStreamer->AddComment("live roots for " +
150                                Twine(FI.getFunction().getName()));
151     AP.OutStreamer->AddBlankLine();
152 
153     for (GCFunctionInfo::iterator J = FI.begin(), JE = FI.end(); J != JE; ++J) {
154       size_t LiveCount = FI.live_size(J);
155       if (LiveCount >= 1 << 16) {
156         // Very rude!
157         report_fatal_error("Function '" + FI.getFunction().getName() +
158                            "' is too large for the ocaml GC! "
159                            "Live root count " +
160                            Twine(LiveCount) + " >= 65536.");
161       }
162 
163       AP.OutStreamer->EmitSymbolValue(J->Label, IntPtrSize);
164       AP.EmitInt16(FrameSize);
165       AP.EmitInt16(LiveCount);
166 
167       for (GCFunctionInfo::live_iterator K = FI.live_begin(J),
168                                          KE = FI.live_end(J);
169            K != KE; ++K) {
170         if (K->StackOffset >= 1 << 16) {
171           // Very rude!
172           report_fatal_error(
173               "GC root stack offset is outside of fixed stack frame and out "
174               "of range for ocaml GC!");
175         }
176         AP.EmitInt16(K->StackOffset);
177       }
178 
179       AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
180     }
181   }
182 }
183