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/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   // If we read this section from an object file, use its original size for the
  33   // padding of the LEB value to avoid changing the file size. Otherwise, pad
  34   // out to 5 bytes to make it predictable, and match the behavior of clang.
  35   unsigned HeaderSecSizeEncodingLen =
  36       S.HeaderSecSizeEncodingLen ? *S.HeaderSecSizeEncodingLen : 5;
  37   encodeULEB128(SectionSize, OS, HeaderSecSizeEncodingLen);
  38   if (HasName) {
  39     encodeULEB128(S.Name.size(), OS);
  40     OS << S.Name;
  41   }
  42   // Total section size is the content size plus 1 for the section type and
  43   // the LEB-encoded size.
  44   SectionSize = SectionSize + 1 + HeaderSecSizeEncodingLen;
  45   return Header;
  46 }
  47
  48 size_t Writer::finalize() {
  49   size_t ObjectSize = sizeof(WasmMagic) + sizeof(WasmVersion);
  50   SectionHeaders.reserve(Obj.Sections.size());
  51   // Finalize the headers of each section so we know the total size.
  52   for (const Section &S : Obj.Sections) {
  53     size_t SectionSize;
  54     SectionHeaders.push_back(createSectionHeader(S, SectionSize));
  55     ObjectSize += SectionSize;
  56   }
  57   return ObjectSize;
  58 }
  59
  60 Error Writer::write() {
  61   size_t TotalSize = finalize();
  62   Out.reserveExtraSpace(TotalSize);
  63
  64   // Write the header.
  65   Out.write(Obj.Header.Magic.data(), Obj.Header.Magic.size());
  66   uint32_t Version;
  67   support::endian::write32le(&Version, Obj.Header.Version);
  68   Out.write(reinterpret_cast<const char *>(&Version), sizeof(Version));
  69
  70   // Write each section.
  71   for (size_t I = 0, S = SectionHeaders.size(); I < S; ++I) {
  72     Out.write(SectionHeaders[I].data(), SectionHeaders[I].size());
  73     Out.write(reinterpret_cast<const char *>(Obj.Sections[I].Contents.data()),
  74               Obj.Sections[I].Contents.size());
  75   }
  76
  77   return Error::success();
  78 }
  79
  80 } // end namespace wasm
  81 } // end namespace objcopy
  82 } // end namespace llvm