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37e39667cc
This removes many SpecificAlloc instantiations and makes my lld (x86-64 Release+Assertions) smaller by ~36k.
93 lines
3.3 KiB
C++
93 lines
3.3 KiB
C++
//===- Thunks.h --------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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 "llvm/ADT/SmallVector.h"
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#include "Relocations.h"
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namespace lld::elf {
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struct Ctx;
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class Defined;
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class InputFile;
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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(Ctx &, Symbol &destination, int64_t addend);
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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 &isec) = 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 §ion);
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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 InputSection and the relocation must be compatible
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// with it.
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virtual bool isCompatibleWith(const InputSection &,
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const Relocation &) const {
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return true;
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}
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// Thunks that indirectly branch to targets may need a synthetic landing
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// pad generated close to the target. For example AArch64 when BTI is
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// enabled.
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virtual bool needsSyntheticLandingPad() { return false; }
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Defined *getThunkTargetSym() const { return syms[0]; }
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Ctx &ctx;
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Symbol &destination;
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int64_t addend;
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// Alternative target when indirect branch to destination can't be used.
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Symbol *landingPad = nullptr;
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llvm::SmallVector<Defined *, 3> syms;
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uint64_t offset = 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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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.
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std::unique_ptr<Thunk> addThunk(Ctx &, const InputSection &isec,
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Relocation &rel);
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// Create a landing pad Thunk for use when indirect branches from Thunks
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// are restricted.
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std::unique_ptr<Thunk> addLandingPadThunk(Ctx &, Symbol &s, int64_t a);
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void writePPC32PltCallStub(Ctx &, uint8_t *buf, uint64_t gotPltVA,
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const InputFile *file, int64_t addend);
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void writePPC64LoadAndBranch(Ctx &, uint8_t *buf, int64_t offset);
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} // namespace lld::elf
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#endif
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