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      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 }
     60