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
15namespace llvm {
16namespace objcopy {
17namespace wasm {
18
19using namespace object;
20using namespace llvm::wasm;
21
22Writer::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(Value: 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(u: 5);
35 encodeULEB128(Value: SectionSize, OS, PadTo: HeaderSecSizeEncodingLen);
36 if (HasName) {
37 encodeULEB128(Value: 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
46size_t Writer::finalize() {
47 size_t ObjectSize = sizeof(WasmMagic) + sizeof(WasmVersion);
48 SectionHeaders.reserve(n: 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(x: createSectionHeader(S, SectionSize));
53 ObjectSize += SectionSize;
54 }
55 return ObjectSize;
56}
57
58Error Writer::write() {
59 size_t TotalSize = finalize();
60 Out.reserveExtraSpace(ExtraSize: TotalSize);
61
62 // Write the header.
63 Out.write(Ptr: Obj.Header.Magic.data(), Size: Obj.Header.Magic.size());
64 uint32_t Version;
65 support::endian::write32le(P: &Version, V: Obj.Header.Version);
66 Out.write(Ptr: reinterpret_cast<const char *>(&Version), Size: sizeof(Version));
67
68 // Write each section.
69 for (size_t I = 0, S = SectionHeaders.size(); I < S; ++I) {
70 Out.write(Ptr: SectionHeaders[I].data(), Size: SectionHeaders[I].size());
71 Out.write(Ptr: reinterpret_cast<const char *>(Obj.Sections[I].Contents.data()),
72 Size: 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