4e920e58e6
In the Atom model the symbols, content and relocations of a relocatable object file are represented as a graph of atoms, where each Atom represents a contiguous block of content with a single name (or no name at all if the content is anonymous), and where edges between Atoms represent relocations. If more than one symbol is associated with a contiguous block of content then the content is broken into multiple atoms and layout constraints (represented by edges) are introduced to ensure that the content remains effectively contiguous. These layout constraints must be kept in mind when examining the content associated with a symbol (it may be spread over multiple atoms) or when applying certain relocation types (e.g. MachO subtractors). This patch replaces the Atom model in JITLink with a blocks-and-symbols model. The blocks-and-symbols model represents relocatable object files as bipartite graphs, with one set of nodes representing contiguous content (Blocks) and another representing named or anonymous locations (Symbols) within a Block. Relocations are represented as edges from Blocks to Symbols. This scheme removes layout constraints (simplifying handling of MachO alt-entry symbols, and hopefully ELF sections at some point in the future) and simplifies some relocation logic. llvm-svn: 373689
82 lines
2.6 KiB
C++
82 lines
2.6 KiB
C++
//===--- BasicGOTAndStubsBuilder.h - Generic GOT/Stub creation --*- C++ -*-===//
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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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//
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// A base for simple GOT and stub creation.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIB_EXECUTIONENGINE_JITLINK_BASICGOTANDSTUBSBUILDER_H
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#define LLVM_LIB_EXECUTIONENGINE_JITLINK_BASICGOTANDSTUBSBUILDER_H
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#include "llvm/ExecutionEngine/JITLink/JITLink.h"
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namespace llvm {
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namespace jitlink {
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template <typename BuilderImpl> class BasicGOTAndStubsBuilder {
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public:
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BasicGOTAndStubsBuilder(LinkGraph &G) : G(G) {}
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void run() {
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// We're going to be adding new blocks, but we don't want to iterate over
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// the newly added ones, so just copy the existing blocks out.
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std::vector<Block *> Blocks(G.blocks().begin(), G.blocks().end());
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for (auto *B : Blocks)
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for (auto &E : B->edges())
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if (impl().isGOTEdge(E))
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impl().fixGOTEdge(E, getGOTEntrySymbol(E.getTarget()));
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else if (impl().isExternalBranchEdge(E))
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impl().fixExternalBranchEdge(E, getStubSymbol(E.getTarget()));
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}
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protected:
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Symbol &getGOTEntrySymbol(Symbol &Target) {
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assert(Target.hasName() && "GOT edge cannot point to anonymous target");
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auto GOTEntryI = GOTEntries.find(Target.getName());
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// Build the entry if it doesn't exist.
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if (GOTEntryI == GOTEntries.end()) {
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auto &GOTEntry = impl().createGOTEntry(Target);
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GOTEntryI =
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GOTEntries.insert(std::make_pair(Target.getName(), &GOTEntry)).first;
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}
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assert(GOTEntryI != GOTEntries.end() && "Could not get GOT entry symbol");
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return *GOTEntryI->second;
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}
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Symbol &getStubSymbol(Symbol &Target) {
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assert(Target.hasName() &&
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"External branch edge can not point to an anonymous target");
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auto StubI = Stubs.find(Target.getName());
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if (StubI == Stubs.end()) {
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auto &StubSymbol = impl().createStub(Target);
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StubI = Stubs.insert(std::make_pair(Target.getName(), &StubSymbol)).first;
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}
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assert(StubI != Stubs.end() && "Count not get stub symbol");
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return *StubI->second;
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}
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LinkGraph &G;
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private:
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BuilderImpl &impl() { return static_cast<BuilderImpl &>(*this); }
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DenseMap<StringRef, Symbol *> GOTEntries;
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DenseMap<StringRef, Symbol *> Stubs;
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};
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} // end namespace jitlink
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} // end namespace llvm
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#endif // LLVM_LIB_EXECUTIONENGINE_JITLINK_BASICGOTANDSTUBSBUILDER_H
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