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/ADT/STLExtras.h"
15 #include "llvm/ADT/SmallString.h"
16 #include "llvm/ADT/Twine.h"
17 #include "llvm/CodeGen/AsmPrinter.h"
18 #include "llvm/CodeGen/BuiltinGCs.h"
19 #include "llvm/CodeGen/GCMetadata.h"
20 #include "llvm/CodeGen/GCMetadataPrinter.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/Function.h"
23 #include "llvm/IR/Mangler.h"
24 #include "llvm/IR/Module.h"
25 #include "llvm/MC/MCContext.h"
26 #include "llvm/MC/MCDirectives.h"
27 #include "llvm/MC/MCStreamer.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Target/TargetLoweringObjectFile.h"
30 #include <cctype>
31 #include <cstddef>
32 #include <cstdint>
33 #include <string>
34 
35 using namespace llvm;
36 
37 namespace {
38 
39 class OcamlGCMetadataPrinter : public GCMetadataPrinter {
40 public:
41   void beginAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
42   void finishAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
43 };
44 
45 } // end anonymous namespace
46 
47 static GCMetadataPrinterRegistry::Add<OcamlGCMetadataPrinter>
48     Y("ocaml", "ocaml 3.10-compatible collector");
49 
50 void llvm::linkOcamlGCPrinter() {}
51 
52 static void EmitCamlGlobal(const Module &M, AsmPrinter &AP, const char *Id) {
53   const std::string &MId = M.getModuleIdentifier();
54 
55   std::string SymName;
56   SymName += "caml";
57   size_t Letter = SymName.size();
58   SymName.append(MId.begin(), llvm::find(MId, '.'));
59   SymName += "__";
60   SymName += Id;
61 
62   // Capitalize the first letter of the module name.
63   SymName[Letter] = toupper(SymName[Letter]);
64 
65   SmallString<128> TmpStr;
66   Mangler::getNameWithPrefix(TmpStr, SymName, M.getDataLayout());
67 
68   MCSymbol *Sym = AP.OutContext.getOrCreateSymbol(TmpStr);
69 
70   AP.OutStreamer->EmitSymbolAttribute(Sym, MCSA_Global);
71   AP.OutStreamer->EmitLabel(Sym);
72 }
73 
74 void OcamlGCMetadataPrinter::beginAssembly(Module &M, GCModuleInfo &Info,
75                                            AsmPrinter &AP) {
76   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getTextSection());
77   EmitCamlGlobal(M, AP, "code_begin");
78 
79   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getDataSection());
80   EmitCamlGlobal(M, AP, "data_begin");
81 }
82 
83 /// emitAssembly - Print the frametable. The ocaml frametable format is thus:
84 ///
85 ///   extern "C" struct align(sizeof(intptr_t)) {
86 ///     uint16_t NumDescriptors;
87 ///     struct align(sizeof(intptr_t)) {
88 ///       void *ReturnAddress;
89 ///       uint16_t FrameSize;
90 ///       uint16_t NumLiveOffsets;
91 ///       uint16_t LiveOffsets[NumLiveOffsets];
92 ///     } Descriptors[NumDescriptors];
93 ///   } caml${module}__frametable;
94 ///
95 /// Note that this precludes programs from stack frames larger than 64K
96 /// (FrameSize and LiveOffsets would overflow). FrameTablePrinter will abort if
97 /// either condition is detected in a function which uses the GC.
98 ///
99 void OcamlGCMetadataPrinter::finishAssembly(Module &M, GCModuleInfo &Info,
100                                             AsmPrinter &AP) {
101   unsigned IntPtrSize = M.getDataLayout().getPointerSize();
102 
103   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getTextSection());
104   EmitCamlGlobal(M, AP, "code_end");
105 
106   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getDataSection());
107   EmitCamlGlobal(M, AP, "data_end");
108 
109   // FIXME: Why does ocaml emit this??
110   AP.OutStreamer->EmitIntValue(0, IntPtrSize);
111 
112   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getDataSection());
113   EmitCamlGlobal(M, AP, "frametable");
114 
115   int NumDescriptors = 0;
116   for (GCModuleInfo::FuncInfoVec::iterator I = Info.funcinfo_begin(),
117                                            IE = Info.funcinfo_end();
118        I != IE; ++I) {
119     GCFunctionInfo &FI = **I;
120     if (FI.getStrategy().getName() != getStrategy().getName())
121       // this function is managed by some other GC
122       continue;
123     for (GCFunctionInfo::iterator J = FI.begin(), JE = FI.end(); J != JE; ++J) {
124       NumDescriptors++;
125     }
126   }
127 
128   if (NumDescriptors >= 1 << 16) {
129     // Very rude!
130     report_fatal_error(" Too much descriptor for ocaml GC");
131   }
132   AP.emitInt16(NumDescriptors);
133   AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
134 
135   for (GCModuleInfo::FuncInfoVec::iterator I = Info.funcinfo_begin(),
136                                            IE = Info.funcinfo_end();
137        I != IE; ++I) {
138     GCFunctionInfo &FI = **I;
139     if (FI.getStrategy().getName() != getStrategy().getName())
140       // this function is managed by some other GC
141       continue;
142 
143     uint64_t FrameSize = FI.getFrameSize();
144     if (FrameSize >= 1 << 16) {
145       // Very rude!
146       report_fatal_error("Function '" + FI.getFunction().getName() +
147                          "' is too large for the ocaml GC! "
148                          "Frame size " +
149                          Twine(FrameSize) + ">= 65536.\n"
150                                             "(" +
151                          Twine(uintptr_t(&FI)) + ")");
152     }
153 
154     AP.OutStreamer->AddComment("live roots for " +
155                                Twine(FI.getFunction().getName()));
156     AP.OutStreamer->AddBlankLine();
157 
158     for (GCFunctionInfo::iterator J = FI.begin(), JE = FI.end(); J != JE; ++J) {
159       size_t LiveCount = FI.live_size(J);
160       if (LiveCount >= 1 << 16) {
161         // Very rude!
162         report_fatal_error("Function '" + FI.getFunction().getName() +
163                            "' is too large for the ocaml GC! "
164                            "Live root count " +
165                            Twine(LiveCount) + " >= 65536.");
166       }
167 
168       AP.OutStreamer->EmitSymbolValue(J->Label, IntPtrSize);
169       AP.emitInt16(FrameSize);
170       AP.emitInt16(LiveCount);
171 
172       for (GCFunctionInfo::live_iterator K = FI.live_begin(J),
173                                          KE = FI.live_end(J);
174            K != KE; ++K) {
175         if (K->StackOffset >= 1 << 16) {
176           // Very rude!
177           report_fatal_error(
178               "GC root stack offset is outside of fixed stack frame and out "
179               "of range for ocaml GC!");
180         }
181         AP.emitInt16(K->StackOffset);
182       }
183 
184       AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
185     }
186   }
187 }
188