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 83