1 //===- OcamlGCPrinter.cpp - Ocaml frametable emitter ----------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements printing the assembly code for an Ocaml frametable.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/ADT/STLExtras.h"
14 #include "llvm/ADT/SmallString.h"
15 #include "llvm/ADT/Twine.h"
16 #include "llvm/CodeGen/AsmPrinter.h"
17 #include "llvm/CodeGen/BuiltinGCs.h"
18 #include "llvm/CodeGen/GCMetadata.h"
19 #include "llvm/CodeGen/GCMetadataPrinter.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/IR/Mangler.h"
23 #include "llvm/IR/Module.h"
24 #include "llvm/MC/MCContext.h"
25 #include "llvm/MC/MCDirectives.h"
26 #include "llvm/MC/MCStreamer.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Target/TargetLoweringObjectFile.h"
29 #include <cctype>
30 #include <cstddef>
31 #include <cstdint>
32 #include <string>
33 
34 using namespace llvm;
35 
36 namespace {
37 
38 class OcamlGCMetadataPrinter : public GCMetadataPrinter {
39 public:
40   void beginAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
41   void finishAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
42 };
43 
44 } // end anonymous namespace
45 
46 static GCMetadataPrinterRegistry::Add<OcamlGCMetadataPrinter>
47     Y("ocaml", "ocaml 3.10-compatible collector");
48 
49 void llvm::linkOcamlGCPrinter() {}
50 
51 static void EmitCamlGlobal(const Module &M, AsmPrinter &AP, const char *Id) {
52   const std::string &MId = M.getModuleIdentifier();
53 
54   std::string SymName;
55   SymName += "caml";
56   size_t Letter = SymName.size();
57   SymName.append(MId.begin(), llvm::find(MId, '.'));
58   SymName += "__";
59   SymName += Id;
60 
61   // Capitalize the first letter of the module name.
62   SymName[Letter] = toupper(SymName[Letter]);
63 
64   SmallString<128> TmpStr;
65   Mangler::getNameWithPrefix(TmpStr, SymName, M.getDataLayout());
66 
67   MCSymbol *Sym = AP.OutContext.getOrCreateSymbol(TmpStr);
68 
69   AP.OutStreamer->EmitSymbolAttribute(Sym, MCSA_Global);
70   AP.OutStreamer->EmitLabel(Sym);
71 }
72 
73 void OcamlGCMetadataPrinter::beginAssembly(Module &M, GCModuleInfo &Info,
74                                            AsmPrinter &AP) {
75   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getTextSection());
76   EmitCamlGlobal(M, AP, "code_begin");
77 
78   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getDataSection());
79   EmitCamlGlobal(M, AP, "data_begin");
80 }
81 
82 /// emitAssembly - Print the frametable. The ocaml frametable format is thus:
83 ///
84 ///   extern "C" struct align(sizeof(intptr_t)) {
85 ///     uint16_t NumDescriptors;
86 ///     struct align(sizeof(intptr_t)) {
87 ///       void *ReturnAddress;
88 ///       uint16_t FrameSize;
89 ///       uint16_t NumLiveOffsets;
90 ///       uint16_t LiveOffsets[NumLiveOffsets];
91 ///     } Descriptors[NumDescriptors];
92 ///   } caml${module}__frametable;
93 ///
94 /// Note that this precludes programs from stack frames larger than 64K
95 /// (FrameSize and LiveOffsets would overflow). FrameTablePrinter will abort if
96 /// either condition is detected in a function which uses the GC.
97 ///
98 void OcamlGCMetadataPrinter::finishAssembly(Module &M, GCModuleInfo &Info,
99                                             AsmPrinter &AP) {
100   unsigned IntPtrSize = M.getDataLayout().getPointerSize();
101 
102   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getTextSection());
103   EmitCamlGlobal(M, AP, "code_end");
104 
105   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getDataSection());
106   EmitCamlGlobal(M, AP, "data_end");
107 
108   // FIXME: Why does ocaml emit this??
109   AP.OutStreamer->EmitIntValue(0, IntPtrSize);
110 
111   AP.OutStreamer->SwitchSection(AP.getObjFileLowering().getDataSection());
112   EmitCamlGlobal(M, AP, "frametable");
113 
114   int NumDescriptors = 0;
115   for (GCModuleInfo::FuncInfoVec::iterator I = Info.funcinfo_begin(),
116                                            IE = Info.funcinfo_end();
117        I != IE; ++I) {
118     GCFunctionInfo &FI = **I;
119     if (FI.getStrategy().getName() != getStrategy().getName())
120       // this function is managed by some other GC
121       continue;
122     for (GCFunctionInfo::iterator J = FI.begin(), JE = FI.end(); J != JE; ++J) {
123       NumDescriptors++;
124     }
125   }
126 
127   if (NumDescriptors >= 1 << 16) {
128     // Very rude!
129     report_fatal_error(" Too much descriptor for ocaml GC");
130   }
131   AP.emitInt16(NumDescriptors);
132   AP.EmitAlignment(IntPtrSize == 4 ? Align(4) : Align(8));
133 
134   for (GCModuleInfo::FuncInfoVec::iterator I = Info.funcinfo_begin(),
135                                            IE = Info.funcinfo_end();
136        I != IE; ++I) {
137     GCFunctionInfo &FI = **I;
138     if (FI.getStrategy().getName() != getStrategy().getName())
139       // this function is managed by some other GC
140       continue;
141 
142     uint64_t FrameSize = FI.getFrameSize();
143     if (FrameSize >= 1 << 16) {
144       // Very rude!
145       report_fatal_error("Function '" + FI.getFunction().getName() +
146                          "' is too large for the ocaml GC! "
147                          "Frame size " +
148                          Twine(FrameSize) + ">= 65536.\n"
149                                             "(" +
150                          Twine(uintptr_t(&FI)) + ")");
151     }
152 
153     AP.OutStreamer->AddComment("live roots for " +
154                                Twine(FI.getFunction().getName()));
155     AP.OutStreamer->AddBlankLine();
156 
157     for (GCFunctionInfo::iterator J = FI.begin(), JE = FI.end(); J != JE; ++J) {
158       size_t LiveCount = FI.live_size(J);
159       if (LiveCount >= 1 << 16) {
160         // Very rude!
161         report_fatal_error("Function '" + FI.getFunction().getName() +
162                            "' is too large for the ocaml GC! "
163                            "Live root count " +
164                            Twine(LiveCount) + " >= 65536.");
165       }
166 
167       AP.OutStreamer->EmitSymbolValue(J->Label, IntPtrSize);
168       AP.emitInt16(FrameSize);
169       AP.emitInt16(LiveCount);
170 
171       for (GCFunctionInfo::live_iterator K = FI.live_begin(J),
172                                          KE = FI.live_end(J);
173            K != KE; ++K) {
174         if (K->StackOffset >= 1 << 16) {
175           // Very rude!
176           report_fatal_error(
177               "GC root stack offset is outside of fixed stack frame and out "
178               "of range for ocaml GC!");
179         }
180         AP.emitInt16(K->StackOffset);
181       }
182 
183       AP.EmitAlignment(IntPtrSize == 4 ? Align(4) : Align(8));
184     }
185   }
186 }
187