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
16namespace llvm {
17namespace objcopy {
18namespace wasm {
19
20using namespace object;
21using namespace llvm::wasm;
22
23Writer::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(Value: 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(Value: SectionSize, OS, PadTo: HeaderSecSizeEncodingLen);
38 if (HasName) {
39 encodeULEB128(Value: 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
48size_t Writer::finalize() {
49 size_t ObjectSize = sizeof(WasmMagic) + sizeof(WasmVersion);
50 SectionHeaders.reserve(n: 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(x: createSectionHeader(S, SectionSize));
55 ObjectSize += SectionSize;
56 }
57 return ObjectSize;
58}
59
60Error Writer::write() {
61 size_t TotalSize = finalize();
62 Out.reserveExtraSpace(ExtraSize: TotalSize);
63
64 // Write the header.
65 Out.write(Ptr: Obj.Header.Magic.data(), Size: Obj.Header.Magic.size());
66 uint32_t Version;
67 support::endian::write32le(P: &Version, V: Obj.Header.Version);
68 Out.write(Ptr: reinterpret_cast<const char *>(&Version), Size: sizeof(Version));
69
70 // Write each section.
71 for (size_t I = 0, S = SectionHeaders.size(); I < S; ++I) {
72 Out.write(Ptr: SectionHeaders[I].data(), Size: SectionHeaders[I].size());
73 Out.write(Ptr: reinterpret_cast<const char *>(Obj.Sections[I].Contents.data()),
74 Size: 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