17ed8f2928
Linker might relax adrp + ldr got address loading to adrp + add for local non-preemptible symbols (e.g. hidden/protected symbols in executable). As usually linker doesn't change relocations properly after relaxation, so we have to handle such cases by ourselves. To do that during relocations reading we change LD64 reloc to ADD if instruction mismatch found and introduce FixRelaxationPass that searches for ADRP+ADD pairs and after performing some checks we're replacing ADRP target symbol to already fixed ADDs one. Vladislav Khmelevsky, Advanced Software Technology Lab, Huawei Differential Revision: https://reviews.llvm.org/D138097
64 lines
2.1 KiB
C++
64 lines
2.1 KiB
C++
#include "bolt/Passes/FixRelaxationPass.h"
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#include "bolt/Core/ParallelUtilities.h"
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using namespace llvm;
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namespace llvm {
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namespace bolt {
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// This function finds ADRP+ADD instruction sequences that originally before
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// linker relaxations were ADRP+LDR. We've modified LDR/ADD relocation properly
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// during relocation reading, so its targeting right symbol. As for ADRP its
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// target is wrong before this pass since we won't be able to recognize and
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// properly change R_AARCH64_ADR_GOT_PAGE relocation to
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// R_AARCH64_ADR_PREL_PG_HI21 during relocation reading. Now we're searching for
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// ADRP+ADD sequences, checking that ADRP points to the GOT-table symbol and the
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// target of ADD is another symbol. When found change ADRP symbol reference to
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// the ADDs one.
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void FixRelaxations::runOnFunction(BinaryFunction &BF) {
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BinaryContext &BC = BF.getBinaryContext();
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for (BinaryBasicBlock &BB : BF) {
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for (auto II = BB.begin(); II != BB.end(); ++II) {
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MCInst &Adrp = *II;
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if (BC.MIB->isPseudo(Adrp) || !BC.MIB->isADRP(Adrp))
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continue;
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const MCSymbol *AdrpSymbol = BC.MIB->getTargetSymbol(Adrp);
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if (!AdrpSymbol || AdrpSymbol->getName() != "__BOLT_got_zero")
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continue;
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auto NextII = std::next(II);
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if (NextII == BB.end())
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continue;
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const MCInst &Add = *NextII;
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if (!BC.MIB->matchAdrpAddPair(Adrp, Add))
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continue;
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const MCSymbol *Symbol = BC.MIB->getTargetSymbol(Add);
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if (!Symbol || AdrpSymbol == Symbol)
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continue;
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const int64_t Addend = BC.MIB->getTargetAddend(Add);
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BC.MIB->setOperandToSymbolRef(Adrp, /*OpNum*/ 1, Symbol, Addend,
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BC.Ctx.get(), ELF::R_AARCH64_NONE);
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}
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}
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}
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void FixRelaxations::runOnFunctions(BinaryContext &BC) {
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if (!BC.isAArch64() || !BC.HasRelocations)
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return;
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ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
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runOnFunction(BF);
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};
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ParallelUtilities::runOnEachFunction(
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BC, ParallelUtilities::SchedulingPolicy::SP_INST_LINEAR, WorkFun, nullptr,
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"FixRelaxations");
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}
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} // namespace bolt
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} // namespace llvm
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