48883142de
Fix bug https://bugs.llvm.org/show_bug.cgi?id=38643 In BPFAsmBackend applyFixup(), there is an assertion for FixedValue to be 0. This may not be true, esp. for optimiation level 0. For example, in the above bug, for the following two static variables: @bpf_map_lookup_elem = internal global i8* (i8*, i8*)* inttoptr (i64 1 to i8* (i8*, i8*)*), align 8 @bpf_map_update_elem = internal global i32 (i8*, i8*, i8*, i64)* inttoptr (i64 2 to i32 (i8*, i8*, i8*, i64)*), align 8 The static variable @bpf_map_update_elem will have a symbol offset of 8 and a FK_SecRel_8 with FixupValue 8 will cause the assertion if llvm is built with -DLLVM_ENABLE_ASSERTIONS=ON. The above relocations will not exist if the program is compiled with optimization level -O1 and above as the compiler optimizes those static variables away. In the below error message, -O2 is suggested as this is the common practice. Note that FixedValue = 0 in applyFixup() does exist and is valid, e.g., for the global variable my_map in the above bug. The bpf loader will process them properly for map_id's before loading the program into the kernel. The static variables, which are not optimized away by compiler, may have FK_SecRel_8 relocation with non-zero FixedValue. The patch removed the offending assertion and will issue a hard error as below if the FixedValue in applyFixup() is not 0. $ llc -march=bpf -filetype=obj fixup.ll LLVM ERROR: Unsupported relocation: try to compile with -O2 or above, or check your static variable usage Signed-off-by: Yonghong Song <yhs@fb.com> llvm-svn: 340455
121 lines
4.2 KiB
C++
121 lines
4.2 KiB
C++
//===-- BPFAsmBackend.cpp - BPF Assembler Backend -------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "MCTargetDesc/BPFMCTargetDesc.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/MC/MCAsmBackend.h"
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#include "llvm/MC/MCAssembler.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCFixup.h"
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#include "llvm/MC/MCObjectWriter.h"
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#include "llvm/Support/EndianStream.h"
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#include <cassert>
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#include <cstdint>
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using namespace llvm;
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namespace {
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class BPFAsmBackend : public MCAsmBackend {
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public:
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BPFAsmBackend(support::endianness Endian) : MCAsmBackend(Endian) {}
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~BPFAsmBackend() override = default;
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void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
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const MCValue &Target, MutableArrayRef<char> Data,
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uint64_t Value, bool IsResolved,
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const MCSubtargetInfo *STI) const override;
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std::unique_ptr<MCObjectTargetWriter>
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createObjectTargetWriter() const override;
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// No instruction requires relaxation
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bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
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const MCRelaxableFragment *DF,
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const MCAsmLayout &Layout) const override {
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return false;
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}
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unsigned getNumFixupKinds() const override { return 1; }
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bool mayNeedRelaxation(const MCInst &Inst,
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const MCSubtargetInfo &STI) const override {
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return false;
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}
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void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
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MCInst &Res) const override {}
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bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
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};
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} // end anonymous namespace
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bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
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if ((Count % 8) != 0)
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return false;
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for (uint64_t i = 0; i < Count; i += 8)
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support::endian::write<uint64_t>(OS, 0x15000000, Endian);
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return true;
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}
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void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
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const MCValue &Target,
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MutableArrayRef<char> Data, uint64_t Value,
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bool IsResolved,
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const MCSubtargetInfo *STI) const {
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if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
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if (Value) {
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MCContext &Ctx = Asm.getContext();
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Ctx.reportError(Fixup.getLoc(),
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"Unsupported relocation: try to compile with -O2 or above, "
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"or check your static variable usage");
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}
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} else if (Fixup.getKind() == FK_Data_4) {
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support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
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} else if (Fixup.getKind() == FK_Data_8) {
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support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
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} else if (Fixup.getKind() == FK_PCRel_4) {
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Value = (uint32_t)((Value - 8) / 8);
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if (Endian == support::little) {
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Data[Fixup.getOffset() + 1] = 0x10;
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support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
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} else {
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Data[Fixup.getOffset() + 1] = 0x1;
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support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
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}
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} else {
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assert(Fixup.getKind() == FK_PCRel_2);
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Value = (uint16_t)((Value - 8) / 8);
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support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
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Endian);
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}
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}
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std::unique_ptr<MCObjectTargetWriter>
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BPFAsmBackend::createObjectTargetWriter() const {
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return createBPFELFObjectWriter(0);
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}
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MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
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const MCSubtargetInfo &STI,
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const MCRegisterInfo &MRI,
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const MCTargetOptions &) {
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return new BPFAsmBackend(support::little);
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}
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MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
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const MCSubtargetInfo &STI,
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const MCRegisterInfo &MRI,
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const MCTargetOptions &) {
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return new BPFAsmBackend(support::big);
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}
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