llvm/tools/llvm-objcopy/wasm/Writer.cpp

   1 //===- Writer.cpp ---------------------------------------------------------===//
   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 "Writer.h"
  10 #include "llvm/BinaryFormat/Wasm.h"
  11 #include "llvm/Support/Endian.h"
  12 #include "llvm/Support/Errc.h"
  13 #include "llvm/Support/LEB128.h"
  14 #include "llvm/Support/raw_ostream.h"
  15
  16 namespace llvm {
  17 namespace objcopy {
  18 namespace wasm {
  19
  20 using namespace object;
  21 using namespace llvm::wasm;
  22
  23 Writer::SectionHeader Writer::createSectionHeader(const Section &S,
  24                                                   size_t &SectionSize) {
  25   SectionHeader Header;
  26   raw_svector_ostream OS(Header);
  27   OS << S.SectionType;
  28   bool HasName = S.SectionType == WASM_SEC_CUSTOM;
  29   SectionSize = S.Contents.size();
  30   if (HasName)
  31     SectionSize += getULEB128Size(S.Name.size()) + S.Name.size();
  32   // Pad the LEB value out to 5 bytes to make it a predictable size, and
  33   // match the behavior of clang.
  34   encodeULEB128(SectionSize, OS, 5);
  35   if (HasName) {
  36     encodeULEB128(S.Name.size(), OS);
  37     OS << S.Name;
  38   }
  39   // Total section size is the content size plus 1 for the section type and
  40   // 5 for the LEB-encoded size.
  41   SectionSize = SectionSize + 1 + 5;
  42   return Header;
  43 }
  44
  45 size_t Writer::finalize() {
  46   size_t ObjectSize = sizeof(WasmMagic) + sizeof(WasmVersion);
  47   SectionHeaders.reserve(Obj.Sections.size());
  48   // Finalize the headers of each section so we know the total size.
  49   for (const Section &S : Obj.Sections) {
  50     size_t SectionSize;
  51     SectionHeaders.push_back(createSectionHeader(S, SectionSize));
  52     ObjectSize += SectionSize;
  53   }
  54   return ObjectSize;
  55 }
  56
  57 Error Writer::write() {
  58   size_t TotalSize = finalize();
  59   Out.reserveExtraSpace(TotalSize);
  60
  61   // Write the header.
  62   Out.write(Obj.Header.Magic.data(), Obj.Header.Magic.size());
  63   uint32_t Version;
  64   support::endian::write32le(&Version, Obj.Header.Version);
  65   Out.write(reinterpret_cast<const char *>(&Version), sizeof(Version));
  66
  67   // Write each section.
  68   for (size_t I = 0, S = SectionHeaders.size(); I < S; ++I) {
  69     Out.write(SectionHeaders[I].data(), SectionHeaders[I].size());
  70     Out.write(reinterpret_cast<const char *>(Obj.Sections[I].Contents.data()),
  71               Obj.Sections[I].Contents.size());
  72   }
  73
  74   return Error::success();
  75 }
  76
  77 } // end namespace wasm
  78 } // end namespace objcopy
  79 } // end namespace llvm