forked from OSchip/llvm-project
Simplify handling of predefined symbols.
Given our representation of symbols as section + offset, we can finalize symbols like _end as soon as the section is known. llvm-svn: 313048
This commit is contained in:
Rafael Espindola
parent
f696a22d3c
commit
4d5601608d
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@ -54,7 +54,7 @@ private:
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void sortSections();
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void finalizeSections();
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void addPredefinedSections();
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void addPredefinedSymbols();
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void setReservedSymbolSections();
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std::vector<PhdrEntry *> createPhdrs();
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void removeEmptyPTLoad();
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@ -63,7 +63,7 @@ private:
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void assignFileOffsetsBinary();
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void setPhdrs();
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void fixSectionAlignments();
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void fixPredefinedSymbols();
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void makeMipsGpAbs();
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void openFile();
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void writeTrapInstr();
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void writeHeader();
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@ -198,12 +198,6 @@ template <class ELFT> void Writer<ELFT>::run() {
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parallelForEach(OutputSections,
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[](OutputSection *Sec) { Sec->maybeCompress<ELFT>(); });
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// Generate assignments for predefined symbols (e.g. _end or _etext)
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// before assigning addresses. These symbols may be referred to from
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// the linker script and we need to ensure they have the correct value
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// prior evaluating any expressions using these symbols.
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addPredefinedSymbols();
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Script->assignAddresses();
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Script->allocateHeaders(Phdrs);
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@ -223,7 +217,7 @@ template <class ELFT> void Writer<ELFT>::run() {
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for (OutputSection *Sec : OutputSections)
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Sec->Addr = 0;
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} else {
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fixPredefinedSymbols();
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makeMipsGpAbs();
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}
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// It does not make sense try to open the file if we have error already.
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@ -846,11 +840,11 @@ template <class ELFT> void Writer<ELFT>::addReservedSymbols() {
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if (Script->Opt.HasSections)
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return;
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auto Add = [](StringRef S) {
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return addOptionalRegular<ELFT>(S, Out::ElfHeader, 0, STV_DEFAULT);
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auto Add = [](StringRef S, int64_t Pos = -1) {
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return addOptionalRegular<ELFT>(S, Out::ElfHeader, Pos, STV_DEFAULT);
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};
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ElfSym::Bss = Add("__bss_start");
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ElfSym::Bss = Add("__bss_start", 0);
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ElfSym::End1 = Add("end");
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ElfSym::End2 = Add("_end");
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ElfSym::Etext1 = Add("etext");
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@ -928,7 +922,7 @@ template <class ELFT> void Writer<ELFT>::createSections() {
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// appropriate time. This ensures that the value is going to be correct by the
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// time any references to these symbols are processed and is equivalent to
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// defining these symbols explicitly in the linker script.
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template <class ELFT> void Writer<ELFT>::addPredefinedSymbols() {
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template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
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PhdrEntry *Last = nullptr;
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PhdrEntry *LastRO = nullptr;
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PhdrEntry *LastRW = nullptr;
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@ -943,58 +937,55 @@ template <class ELFT> void Writer<ELFT>::addPredefinedSymbols() {
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LastRO = P;
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}
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auto Make = [](DefinedRegular *S) {
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auto *Cmd = make<SymbolAssignment>(
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S->getName(), [=] { return Script->getSymbolValue("", "."); }, "");
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Cmd->Sym = S;
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return Cmd;
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};
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std::vector<BaseCommand *> &V = Script->Opt.Commands;
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// _end is the first location after the uninitialized data region.
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if (Last) {
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for (size_t I = 0; I < V.size(); ++I) {
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if (V[I] != Last->LastSec)
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continue;
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if (ElfSym::End2)
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V.insert(V.begin() + I + 1, Make(ElfSym::End2));
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if (ElfSym::End1)
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V.insert(V.begin() + I + 1, Make(ElfSym::End1));
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break;
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}
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if (ElfSym::End1)
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ElfSym::End1->Section = Last->LastSec;
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if (ElfSym::End2)
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ElfSym::End2->Section = Last->LastSec;
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}
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// _etext is the first location after the last read-only loadable segment.
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if (LastRO) {
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for (size_t I = 0; I < V.size(); ++I) {
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if (V[I] != LastRO->LastSec)
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continue;
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if (ElfSym::Etext2)
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V.insert(V.begin() + I + 1, Make(ElfSym::Etext2));
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if (ElfSym::Etext1)
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V.insert(V.begin() + I + 1, Make(ElfSym::Etext1));
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break;
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}
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if (ElfSym::Etext1)
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ElfSym::Etext1->Section = LastRO->LastSec;
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if (ElfSym::Etext2)
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ElfSym::Etext2->Section = LastRO->LastSec;
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}
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// _edata points to the end of the last non SHT_NOBITS section.
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if (LastRW) {
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size_t I = 0;
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for (; I < V.size(); ++I)
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if (V[I] == LastRW->FirstSec)
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for (; I < OutputSections.size(); ++I)
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if (OutputSections[I] == LastRW->FirstSec)
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break;
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for (; I < V.size(); ++I) {
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auto *Sec = dyn_cast<OutputSection>(V[I]);
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if (!Sec || Sec->Type != SHT_NOBITS)
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for (; I < OutputSections.size(); ++I) {
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if (OutputSections[I]->Type != SHT_NOBITS)
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continue;
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if (ElfSym::Edata2)
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V.insert(V.begin() + I, Make(ElfSym::Edata2));
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if (ElfSym::Edata1)
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V.insert(V.begin() + I, Make(ElfSym::Edata1));
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break;
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}
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if (ElfSym::Edata1)
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ElfSym::Edata1->Section = OutputSections[I - 1];
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if (ElfSym::Edata2)
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ElfSym::Edata2->Section = OutputSections[I - 1];
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}
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if (ElfSym::Bss)
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ElfSym::Bss->Section = findSection(".bss");
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// Setup MIPS _gp_disp/__gnu_local_gp symbols which should
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// be equal to the _gp symbol's value.
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if (ElfSym::MipsGp && !ElfSym::MipsGp->Value) {
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// Find GP-relative section with the lowest address
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// and use this address to calculate default _gp value.
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for (OutputSection *OS : OutputSections) {
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if (OS->Flags & SHF_MIPS_GPREL) {
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ElfSym::MipsGp->Section = OS;
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ElfSym::MipsGp->Value = 0x7ff0;
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break;
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}
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}
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}
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}
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@ -1360,6 +1351,10 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
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Out::ProgramHeaders->Size = sizeof(Elf_Phdr) * Phdrs.size();
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}
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// Some symbols are defined in term of program headers. Now that we
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// have the headers, we can find out which sections they point to.
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setReservedSymbolSections();
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// Dynamic section must be the last one in this list and dynamic
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// symbol table section (DynSymTab) must be the first one.
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applySynthetic({InX::DynSymTab, InX::Bss,
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@ -1790,25 +1785,11 @@ static uint16_t getELFType() {
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return ET_EXEC;
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}
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// This function is called after we have assigned address and size
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// to each section. This function fixes some predefined
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// symbol values that depend on section address and size.
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template <class ELFT> void Writer<ELFT>::fixPredefinedSymbols() {
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if (ElfSym::Bss)
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ElfSym::Bss->Section = findSection(".bss");
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// Setup MIPS _gp_disp/__gnu_local_gp symbols which should
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// be equal to the _gp symbol's value.
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if (Config->EMachine == EM_MIPS && !ElfSym::MipsGp->Value) {
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// Find GP-relative section with the lowest address
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// and use this address to calculate default _gp value.
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for (const OutputSection *Cmd : OutputSections) {
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const OutputSection *OS = Cmd;
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if (OS->Flags & SHF_MIPS_GPREL) {
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ElfSym::MipsGp->Value = OS->Addr + 0x7ff0;
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break;
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}
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}
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// For some reason we have to make the mips gp symbol absolute.
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template <class ELFT> void Writer<ELFT>::makeMipsGpAbs() {
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if (ElfSym::MipsGp && ElfSym::MipsGp->Section) {
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ElfSym::MipsGp->Value += cast<OutputSection>(ElfSym::MipsGp->Section)->Addr;
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ElfSym::MipsGp->Section = nullptr;
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}
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}
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