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//===--------- DefineExternalSectionStartAndEndSymbols.h --------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Utility class for recognizing external section start and end symbols and
// transforming them into defined symbols for the start and end blocks of the
// associated Section.
#include "llvm/ExecutionEngine/JITLink/JITLink.h"
#include "llvm/Support/Debug.h"
#define DEBUG_TYPE "jitlink"
namespace llvm {
namespace jitlink {
struct SectionRangeSymbolDesc {
SectionRangeSymbolDesc() = default;
SectionRangeSymbolDesc(Section &Sec, bool IsStart)
: Sec(&Sec), IsStart(IsStart) {}
Section *Sec = nullptr;
bool IsStart = false;
/// Pass implementation for the createDefineExternalSectionStartAndEndSymbols
/// function.
template <typename SymbolIdentifierFunction>
class DefineExternalSectionStartAndEndSymbols {
DefineExternalSectionStartAndEndSymbols(SymbolIdentifierFunction F)
: F(std::move(F)) {}
Error operator()(LinkGraph &G) {
// This pass will affect the external symbols set, so copy them out into a
// vector and iterate over that.
std::vector<Symbol *> Externals(G.external_symbols().begin(),
for (auto *Sym : Externals) {
SectionRangeSymbolDesc D = F(G, *Sym);
if (D.Sec) {
auto &SR = getSectionRange(*D.Sec);
if (D.IsStart) {
if (SR.empty())
G.makeAbsolute(*Sym, 0);
G.makeDefined(*Sym, *SR.getFirstBlock(), 0, 0, Linkage::Strong,
Scope::Local, false);
} else {
if (SR.empty())
G.makeAbsolute(*Sym, 0);
G.makeDefined(*Sym, *SR.getLastBlock(),
SR.getLastBlock()->getSize(), 0, Linkage::Strong,
Scope::Local, false);
return Error::success();
SectionRange &getSectionRange(Section &Sec) {
auto I = SectionRanges.find(&Sec);
if (I == SectionRanges.end())
I = SectionRanges.insert(std::make_pair(&Sec, SectionRange(Sec))).first;
return I->second;
DenseMap<Section *, SectionRange> SectionRanges;
SymbolIdentifierFunction F;
/// Returns a JITLink pass (as a function class) that uses the given symbol
/// identification function to identify external section start and end symbols
/// (and their associated Section*s) and transform the identified externals
/// into defined symbols pointing to the start of the first block in the
/// section and the end of the last (start and end symbols for empty sections
/// will be transformed into absolute symbols at address 0).
/// The identification function should be callable as
/// SectionRangeSymbolDesc (LinkGraph &G, Symbol &Sym)
/// If Sym is not a section range start or end symbol then a default
/// constructed SectionRangeSymbolDesc should be returned. If Sym is a start
/// symbol then SectionRangeSymbolDesc(Sec, true), where Sec is a reference to
/// the target Section. If Sym is an end symbol then
/// SectionRangeSymbolDesc(Sec, false) should be returned.
/// This pass should be run in the PostAllocationPass pipeline, at which point
/// all blocks should have been assigned their final addresses.
template <typename SymbolIdentifierFunction>
SymbolIdentifierFunction &&F) {
return DefineExternalSectionStartAndEndSymbols<SymbolIdentifierFunction>(
} // end namespace jitlink
} // end namespace llvm