1 //===-- WebAssemblyELFObjectWriter.cpp - WebAssembly ELF Writer -----------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 ///
10 /// \file
11 /// \brief This file handles ELF-specific object emission, converting LLVM's
12 /// internal fixups into the appropriate relocations.
13 ///
14 //===----------------------------------------------------------------------===//
15
16 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
17 #include "llvm/MC/MCELFObjectWriter.h"
18 #include "llvm/MC/MCFixup.h"
19 #include "llvm/Support/ErrorHandling.h"
20 using namespace llvm;
21
22 namespace {
23 class WebAssemblyELFObjectWriter final : public MCELFObjectTargetWriter {
24 public:
25 WebAssemblyELFObjectWriter(bool Is64Bit, uint8_t OSABI);
26
27 protected:
28 unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
29 const MCFixup &Fixup, bool IsPCRel) const override;
30 };
31 } // end anonymous namespace
32
WebAssemblyELFObjectWriter(bool Is64Bit,uint8_t OSABI)33 WebAssemblyELFObjectWriter::WebAssemblyELFObjectWriter(bool Is64Bit,
34 uint8_t OSABI)
35 : MCELFObjectTargetWriter(Is64Bit, OSABI, ELF::EM_WEBASSEMBLY,
36 /*HasRelocationAddend=*/false) {}
37
getRelocType(MCContext & Ctx,const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const38 unsigned WebAssemblyELFObjectWriter::getRelocType(MCContext &Ctx,
39 const MCValue &Target,
40 const MCFixup &Fixup,
41 bool IsPCRel) const {
42 // WebAssembly functions are not allocated in the address space. To resolve a
43 // pointer to a function, we must use a special relocation type.
44 if (const MCSymbolRefExpr *SyExp =
45 dyn_cast<MCSymbolRefExpr>(Fixup.getValue()))
46 if (SyExp->getKind() == MCSymbolRefExpr::VK_WebAssembly_FUNCTION)
47 return ELF::R_WEBASSEMBLY_FUNCTION;
48
49 switch (Fixup.getKind()) {
50 case FK_Data_4:
51 assert(!is64Bit() && "4-byte relocations only supported on wasm32");
52 return ELF::R_WEBASSEMBLY_DATA;
53 case FK_Data_8:
54 assert(is64Bit() && "8-byte relocations only supported on wasm64");
55 return ELF::R_WEBASSEMBLY_DATA;
56 default:
57 llvm_unreachable("unimplemented fixup kind");
58 }
59 }
60
createWebAssemblyELFObjectWriter(raw_pwrite_stream & OS,bool Is64Bit,uint8_t OSABI)61 MCObjectWriter *llvm::createWebAssemblyELFObjectWriter(raw_pwrite_stream &OS,
62 bool Is64Bit,
63 uint8_t OSABI) {
64 MCELFObjectTargetWriter *MOTW =
65 new WebAssemblyELFObjectWriter(Is64Bit, OSABI);
66 return createELFObjectWriter(MOTW, OS, /*IsLittleEndian=*/true);
67 }
68