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1376d19372
A second binutils feature needed to support ELFv2 is the .localentry
directive. In the ELFv2 ABI, functions may have two entry points:
one for calling the routine locally via "bl", and one for calling the
function via function pointer (either at the source level, or implicitly
via a PLT stub for global calls). The two entry points share a single
ELF symbol, where the ELF symbol address identifies the global entry
point address, while the local entry point is found by adding a delta
offset to the symbol address. That offset is encoded into three
platform-specific bits of the ELF symbol st_other field.
The .localentry directive instructs the assembler to set those fields
to encode a particular offset. This is typically used by a function
prologue sequence like this:
func:
addis r2, r12, (.TOC.-func)@ha
addi r2, r2, (.TOC.-func)@l
.localentry func, .-func
Note that according to the ABI, when calling the global entry point,
r12 must be set to point the global entry point address itself; while
when calling the local entry point, r2 must be set to point to the TOC
base. The two instructions between the global and local entry point in
the above example translate the first requirement into the second.
This patch implements support in the PowerPC MC streamers to emit the
.localentry directive (both into assembler and ELF object output), as
well as support in the assembler parser to parse that directive.
In addition, there is another change required in MC fixup/relocation
handling to properly deal with relocations targeting function symbols
with two entry points: When the target function is known local, the MC
layer would immediately handle the fixup by inserting the target
address -- this is wrong, since the call may need to go to the local
entry point instead. The GNU assembler handles this case by *not*
directly resolving fixups targeting functions with two entry points,
but always emits the relocation and relies on the linker to handle
this case correctly. This patch changes LLVM MC to do the same (this
is done via the processFixupValue routine).
Similarly, there are cases where the assembler would normally emit a
relocation, but "simplify" it to a relocation targeting a *section*
instead of the actual symbol. For the same reason as above, this
may be wrong when the target symbol has two entry points. The GNU
assembler again handles this case by not performing this simplification
in that case, but leaving the relocation targeting the full symbol,
which is then resolved by the linker. This patch changes LLVM MC
to do the same (via the needsRelocateWithSymbol routine).
NOTE: The method used in this patch is overly pessimistic, since the
needsRelocateWithSymbol routine currently does not have access to the
actual target symbol, and thus must always assume that it might have
two entry points. This will be improved upon by a follow-on patch
that modifies common code to pass the target symbol when calling
needsRelocateWithSymbol.
Reviewed by Hal Finkel.
llvm-svn: 213485
246 lines
8.0 KiB
C++
246 lines
8.0 KiB
C++
//===-- PPCAsmBackend.cpp - PPC 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/PPCMCTargetDesc.h"
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#include "MCTargetDesc/PPCFixupKinds.h"
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#include "llvm/MC/MCAssembler.h"
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#include "llvm/MC/MCAsmBackend.h"
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#include "llvm/MC/MCELF.h"
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#include "llvm/MC/MCELFObjectWriter.h"
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#include "llvm/MC/MCFixupKindInfo.h"
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#include "llvm/MC/MCMachObjectWriter.h"
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#include "llvm/MC/MCObjectWriter.h"
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#include "llvm/MC/MCSectionMachO.h"
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#include "llvm/MC/MCValue.h"
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#include "llvm/Support/ELF.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/MachO.h"
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#include "llvm/Support/TargetRegistry.h"
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using namespace llvm;
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static uint64_t adjustFixupValue(unsigned Kind, uint64_t Value) {
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switch (Kind) {
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default:
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llvm_unreachable("Unknown fixup kind!");
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case FK_Data_1:
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case FK_Data_2:
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case FK_Data_4:
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case FK_Data_8:
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case PPC::fixup_ppc_nofixup:
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return Value;
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case PPC::fixup_ppc_brcond14:
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case PPC::fixup_ppc_brcond14abs:
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return Value & 0xfffc;
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case PPC::fixup_ppc_br24:
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case PPC::fixup_ppc_br24abs:
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return Value & 0x3fffffc;
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case PPC::fixup_ppc_half16:
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return Value & 0xffff;
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case PPC::fixup_ppc_half16ds:
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return Value & 0xfffc;
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}
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}
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static unsigned getFixupKindNumBytes(unsigned Kind) {
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switch (Kind) {
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default:
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llvm_unreachable("Unknown fixup kind!");
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case FK_Data_1:
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return 1;
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case FK_Data_2:
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case PPC::fixup_ppc_half16:
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case PPC::fixup_ppc_half16ds:
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return 2;
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case FK_Data_4:
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case PPC::fixup_ppc_brcond14:
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case PPC::fixup_ppc_brcond14abs:
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case PPC::fixup_ppc_br24:
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case PPC::fixup_ppc_br24abs:
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return 4;
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case FK_Data_8:
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return 8;
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case PPC::fixup_ppc_nofixup:
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return 0;
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}
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}
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namespace {
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class PPCAsmBackend : public MCAsmBackend {
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const Target &TheTarget;
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bool IsLittleEndian;
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public:
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PPCAsmBackend(const Target &T, bool isLittle) : MCAsmBackend(), TheTarget(T),
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IsLittleEndian(isLittle) {}
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unsigned getNumFixupKinds() const override {
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return PPC::NumTargetFixupKinds;
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}
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const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override {
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const static MCFixupKindInfo InfosBE[PPC::NumTargetFixupKinds] = {
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// name offset bits flags
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{ "fixup_ppc_br24", 6, 24, MCFixupKindInfo::FKF_IsPCRel },
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{ "fixup_ppc_brcond14", 16, 14, MCFixupKindInfo::FKF_IsPCRel },
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{ "fixup_ppc_br24abs", 6, 24, 0 },
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{ "fixup_ppc_brcond14abs", 16, 14, 0 },
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{ "fixup_ppc_half16", 0, 16, 0 },
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{ "fixup_ppc_half16ds", 0, 14, 0 },
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{ "fixup_ppc_nofixup", 0, 0, 0 }
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};
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const static MCFixupKindInfo InfosLE[PPC::NumTargetFixupKinds] = {
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// name offset bits flags
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{ "fixup_ppc_br24", 2, 24, MCFixupKindInfo::FKF_IsPCRel },
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{ "fixup_ppc_brcond14", 2, 14, MCFixupKindInfo::FKF_IsPCRel },
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{ "fixup_ppc_br24abs", 2, 24, 0 },
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{ "fixup_ppc_brcond14abs", 2, 14, 0 },
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{ "fixup_ppc_half16", 0, 16, 0 },
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{ "fixup_ppc_half16ds", 2, 14, 0 },
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{ "fixup_ppc_nofixup", 0, 0, 0 }
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};
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if (Kind < FirstTargetFixupKind)
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return MCAsmBackend::getFixupKindInfo(Kind);
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assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
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"Invalid kind!");
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return (IsLittleEndian? InfosLE : InfosBE)[Kind - FirstTargetFixupKind];
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}
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void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
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uint64_t Value, bool IsPCRel) const override {
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Value = adjustFixupValue(Fixup.getKind(), Value);
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if (!Value) return; // Doesn't change encoding.
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unsigned Offset = Fixup.getOffset();
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unsigned NumBytes = getFixupKindNumBytes(Fixup.getKind());
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// For each byte of the fragment that the fixup touches, mask in the bits
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// from the fixup value. The Value has been "split up" into the appropriate
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// bitfields above.
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for (unsigned i = 0; i != NumBytes; ++i) {
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unsigned Idx = IsLittleEndian ? i : (NumBytes - 1 - i);
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Data[Offset + i] |= uint8_t((Value >> (Idx * 8)) & 0xff);
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}
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}
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void processFixupValue(const MCAssembler &Asm, const MCAsmLayout &Layout,
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const MCFixup &Fixup, const MCFragment *DF,
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const MCValue &Target, uint64_t &Value,
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bool &IsResolved) override {
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switch ((PPC::Fixups)Fixup.getKind()) {
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default: break;
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case PPC::fixup_ppc_br24:
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case PPC::fixup_ppc_br24abs:
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// If the target symbol has a local entry point we must not attempt
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// to resolve the fixup directly. Emit a relocation and leave
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// resolution of the final target address to the linker.
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if (const MCSymbolRefExpr *A = Target.getSymA()) {
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const MCSymbolData &Data = Asm.getSymbolData(A->getSymbol());
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// The "other" values are stored in the last 6 bits of the second byte.
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// The traditional defines for STO values assume the full byte and thus
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// the shift to pack it.
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unsigned Other = MCELF::getOther(Data) << 2;
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if ((Other & ELF::STO_PPC64_LOCAL_MASK) != 0)
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IsResolved = false;
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}
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break;
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}
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}
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bool mayNeedRelaxation(const MCInst &Inst) const override {
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// FIXME.
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return false;
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}
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bool fixupNeedsRelaxation(const MCFixup &Fixup,
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uint64_t Value,
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const MCRelaxableFragment *DF,
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const MCAsmLayout &Layout) const override {
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// FIXME.
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llvm_unreachable("relaxInstruction() unimplemented");
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}
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void relaxInstruction(const MCInst &Inst, MCInst &Res) const override {
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// FIXME.
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llvm_unreachable("relaxInstruction() unimplemented");
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}
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bool writeNopData(uint64_t Count, MCObjectWriter *OW) const override {
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uint64_t NumNops = Count / 4;
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for (uint64_t i = 0; i != NumNops; ++i)
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OW->Write32(0x60000000);
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switch (Count % 4) {
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default: break; // No leftover bytes to write
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case 1: OW->Write8(0); break;
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case 2: OW->Write16(0); break;
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case 3: OW->Write16(0); OW->Write8(0); break;
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}
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return true;
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}
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unsigned getPointerSize() const {
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StringRef Name = TheTarget.getName();
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if (Name == "ppc64" || Name == "ppc64le") return 8;
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assert(Name == "ppc32" && "Unknown target name!");
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return 4;
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}
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bool isLittleEndian() const {
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return IsLittleEndian;
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}
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};
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} // end anonymous namespace
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// FIXME: This should be in a separate file.
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namespace {
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class DarwinPPCAsmBackend : public PPCAsmBackend {
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public:
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DarwinPPCAsmBackend(const Target &T) : PPCAsmBackend(T, false) { }
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MCObjectWriter *createObjectWriter(raw_ostream &OS) const override {
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bool is64 = getPointerSize() == 8;
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return createPPCMachObjectWriter(
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OS,
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/*Is64Bit=*/is64,
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(is64 ? MachO::CPU_TYPE_POWERPC64 : MachO::CPU_TYPE_POWERPC),
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MachO::CPU_SUBTYPE_POWERPC_ALL);
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}
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};
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class ELFPPCAsmBackend : public PPCAsmBackend {
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uint8_t OSABI;
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public:
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ELFPPCAsmBackend(const Target &T, bool IsLittleEndian, uint8_t OSABI) :
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PPCAsmBackend(T, IsLittleEndian), OSABI(OSABI) { }
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MCObjectWriter *createObjectWriter(raw_ostream &OS) const override {
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bool is64 = getPointerSize() == 8;
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return createPPCELFObjectWriter(OS, is64, isLittleEndian(), OSABI);
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}
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};
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} // end anonymous namespace
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MCAsmBackend *llvm::createPPCAsmBackend(const Target &T,
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const MCRegisterInfo &MRI,
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StringRef TT, StringRef CPU) {
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if (Triple(TT).isOSDarwin())
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return new DarwinPPCAsmBackend(T);
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uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(Triple(TT).getOS());
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bool IsLittleEndian = Triple(TT).getArch() == Triple::ppc64le;
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return new ELFPPCAsmBackend(T, IsLittleEndian, OSABI);
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}
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