lib/MC/MCLinkerOptimizationHint.cpp

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