LLVM 18.0.0git
WasmWriter.cpp
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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"
11#include "llvm/Support/Endian.h"
12#include "llvm/Support/Errc.h"
13#include "llvm/Support/LEB128.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(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
48size_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
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;
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
#define I(x, y, z)
Definition: MD5.cpp:58
raw_pwrite_stream & OS
Lightweight error class with error context and mandatory checking.
Definition: Error.h:160
static ErrorSuccess success()
Create a success value.
Definition: Error.h:334
constexpr size_t size() const
size - Get the string size.
Definition: StringRef.h:137
const char * data() const
data - Get a pointer to the start of the string (which may not be null terminated).
Definition: StringRef.h:131
raw_ostream & write(unsigned char C)
virtual void reserveExtraSpace(uint64_t ExtraSize)
If possible, pre-allocate ExtraSize bytes for stream data.
Definition: raw_ostream.h:147
A raw_ostream that writes to an SmallVector or SmallString.
Definition: raw_ostream.h:672
@ SectionSize
Definition: COFF.h:60
void write32le(void *P, uint32_t V)
Definition: Endian.h:414
const char WasmMagic[]
Definition: Wasm.h:26
const uint32_t WasmVersion
Definition: Wasm.h:28
@ WASM_SEC_CUSTOM
Definition: Wasm.h:242
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
auto size(R &&Range, std::enable_if_t< std::is_base_of< std::random_access_iterator_tag, typename std::iterator_traits< decltype(Range.begin())>::iterator_category >::value, void > *=nullptr)
Get the size of a range.
Definition: STLExtras.h:1685
unsigned getULEB128Size(uint64_t Value)
Utility function to get the size of the ULEB128-encoded value.
Definition: LEB128.cpp:19
unsigned encodeULEB128(uint64_t Value, raw_ostream &OS, unsigned PadTo=0)
Utility function to encode a ULEB128 value to an output stream.
Definition: LEB128.h:80
std::vector< Section > Sections
Definition: WasmObject.h:34
llvm::wasm::WasmObjectHeader Header
Definition: WasmObject.h:32