llvm/lib/CodeGen/AsmPrinter/OcamlGCPrinter.cpp

   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/GCMetadata.h"
  18 #include "llvm/CodeGen/GCMetadataPrinter.h"
  19 #include "llvm/IR/BuiltinGCs.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 (std::unique_ptr<GCFunctionInfo> &FI :
 116        llvm::make_range(Info.funcinfo_begin(), Info.funcinfo_end())) {
 117     if (FI->getStrategy().getName() != getStrategy().getName())
 118       // this function is managed by some other GC
 119       continue;
 120     NumDescriptors += FI->size();
 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 ? Align(4) : Align(8));
 129
 130   for (std::unique_ptr<GCFunctionInfo> &FI :
 131        llvm::make_range(Info.funcinfo_begin(), Info.funcinfo_end())) {
 132     if (FI->getStrategy().getName() != getStrategy().getName())
 133       // this function is managed by some other GC
 134       continue;
 135
 136     uint64_t FrameSize = FI->getFrameSize();
 137     if (FrameSize >= 1 << 16) {
 138       // Very rude!
 139       report_fatal_error("Function '" + FI->getFunction().getName() +
 140                          "' is too large for the ocaml GC! "
 141                          "Frame size " +
 142                          Twine(FrameSize) +
 143                          ">= 65536.\n"
 144                          "(" +
 145                          Twine(reinterpret_cast<uintptr_t>(FI.get())) + ")");
 146     }
 147
 148     AP.OutStreamer->AddComment("live roots for " +
 149                                Twine(FI->getFunction().getName()));
 150     AP.OutStreamer->addBlankLine();
 151
 152     for (GCFunctionInfo::iterator J = FI->begin(), JE = FI->end(); J != JE;
 153          ++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 ? Align(4) : Align(8));
 180     }
 181   }
 182 }