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