lib/MC/MCLinkerOptimizationHint.cpp

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