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 81