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72 lines
2.4 KiB
C++
72 lines
2.4 KiB
C++
//===- Thunks.h --------------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLD_ELF_THUNKS_H
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#define LLD_ELF_THUNKS_H
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#include "Relocations.h"
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namespace lld {
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namespace elf {
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class Defined;
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class Symbol;
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class ThunkSection;
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// Class to describe an instance of a Thunk.
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// A Thunk is a code-sequence inserted by the linker in between a caller and
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// the callee. The relocation to the callee is redirected to the Thunk, which
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// after executing transfers control to the callee. Typical uses of Thunks
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// include transferring control from non-pi to pi and changing state on
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// targets like ARM.
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//
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// Thunks can be created for Defined, Shared and Undefined Symbols.
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// Thunks are assigned to synthetic ThunkSections
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class Thunk {
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public:
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Thunk(Symbol &Destination);
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virtual ~Thunk();
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virtual uint32_t size() = 0;
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virtual void writeTo(uint8_t *Buf) = 0;
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// All Thunks must define at least one symbol, known as the thunk target
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// symbol, so that we can redirect relocations to it. The thunk may define
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// additional symbols, but these are never targets for relocations.
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virtual void addSymbols(ThunkSection &IS) = 0;
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void setOffset(uint64_t Offset);
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Defined *addSymbol(StringRef Name, uint8_t Type, uint64_t Value,
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InputSectionBase &Section);
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// Some Thunks must be placed immediately before their Target as they elide
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// a branch and fall through to the first Symbol in the Target.
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virtual InputSection *getTargetInputSection() const { return nullptr; }
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// To reuse a Thunk the caller as identified by the Type must be
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// compatible with it.
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virtual bool isCompatibleWith(RelType Type) const { return true; }
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Defined *getThunkTargetSym() const { return Syms[0]; }
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// The alignment requirement for this Thunk, defaults to the size of the
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// typical code section alignment.
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Symbol &Destination;
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llvm::SmallVector<Defined *, 3> Syms;
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uint64_t Offset = 0;
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uint32_t Alignment = 4;
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};
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// For a Relocation to symbol S create a Thunk to be added to a synthetic
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// ThunkSection. At present there are implementations for ARM and Mips Thunks.
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Thunk *addThunk(RelType Type, Symbol &S);
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} // namespace elf
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} // namespace lld
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#endif
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