lib/MC/MCLinkerOptimizationHint.cpp

   1 //===- llvm/MC/MCLinkerOptimizationHint.cpp ----- LOH handling ------------===//
   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 #include "llvm/MC/MCLinkerOptimizationHint.h"
  11 #include "llvm/MC/MCAsmLayout.h"
  12 #include "llvm/MC/MCMachObjectWriter.h"
  13 #include "llvm/Support/LEB128.h"
  14 #include "llvm/Support/raw_ostream.h"
  15 #include <cstddef>
  16 #include <cstdint>
  17
  18 using namespace llvm;
  19
  20 // Each LOH is composed by, in this order (each field is encoded using ULEB128):
  21 // - Its kind.
  22 // - Its number of arguments (let say N).
  23 // - Its arg1.
  24 // - ...
  25 // - Its argN.
  26 // <arg1> to <argN> are absolute addresses in the object file, i.e.,
  27 // relative addresses from the beginning of the object file.
  28 void MCLOHDirective::emit_impl(raw_ostream &OutStream,
  29                                const MachObjectWriter &ObjWriter,
  30                                const MCAsmLayout &Layout) const {
  31   encodeULEB128(Kind, OutStream);
  32   encodeULEB128(Args.size(), OutStream);
  33   for (const MCSymbol *Arg : Args)
  34     encodeULEB128(ObjWriter.getSymbolAddress(*Arg, Layout), OutStream);
  35 }
  36
  37 void MCLOHDirective::emit(MachObjectWriter &ObjWriter,
  38                           const MCAsmLayout &Layout) const {
  39   raw_ostream &OutStream = ObjWriter.W.OS;
  40   emit_impl(OutStream, ObjWriter, Layout);
  41 }
  42
  43 uint64_t MCLOHDirective::getEmitSize(const MachObjectWriter &ObjWriter,
  44                                      const MCAsmLayout &Layout) const {
  45   class raw_counting_ostream : public raw_ostream {
  46     uint64_t Count = 0;
  47
  48     void write_impl(const char *, size_t size) override { Count += size; }
  49
  50     uint64_t current_pos() const override { return Count; }
  51
  52   public:
  53     raw_counting_ostream() = default;
  54     ~raw_counting_ostream() override { flush(); }
  55   };
  56
  57   raw_counting_ostream OutStream;
  58   emit_impl(OutStream, ObjWriter, Layout);
  59   return OutStream.tell();
  60 }