llvm/lib/ObjCopy/wasm/WasmWriter.cpp

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