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bed00d3292
The builtin function
u32 btf_type_id = __builtin_btf_type_id(param, 0)
can help preserve type info for the following use case:
extern void foo(..., void *data, int size);
int test(...) {
struct t { int a; int b; int c; } d;
d.a = ...; d.b = ...; d.c = ...;
foo(..., &d, sizeof(d));
}
The function "foo" in the above only see raw data and does not
know what type of the data is. In certain cases, e.g., logging,
the additional type information will help pretty print.
This patch handles the builtin in BPF backend. It includes
an IR pass to translate the IR intrinsic to a load of
a global variable which carries the metadata, and an MI
pass to remove the intermediate load of the global variable.
Finally, in AsmPrinter pass, proper instruction are generated.
In the above example, the second argument for __builtin_btf_type_id()
is 0, which means a relocation for local adjustment,
i.e., w.r.t. bpf program BTF change, will be generated.
The value 1 for the second argument means
a relocation for remote adjustment, e.g., against vmlinux.
Differential Revision: https://reviews.llvm.org/D74572
134 lines
4.4 KiB
C++
134 lines
4.4 KiB
C++
//===-- BPFTargetMachine.cpp - Define TargetMachine for BPF ---------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Implements the info about BPF target spec.
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//
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//===----------------------------------------------------------------------===//
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#include "BPFTargetMachine.h"
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#include "BPF.h"
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#include "MCTargetDesc/BPFMCAsmInfo.h"
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#include "TargetInfo/BPFTargetInfo.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
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#include "llvm/CodeGen/TargetPassConfig.h"
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#include "llvm/IR/LegacyPassManager.h"
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#include "llvm/Support/FormattedStream.h"
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#include "llvm/Support/TargetRegistry.h"
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#include "llvm/Target/TargetOptions.h"
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using namespace llvm;
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static cl::
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opt<bool> DisableMIPeephole("disable-bpf-peephole", cl::Hidden,
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cl::desc("Disable machine peepholes for BPF"));
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extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeBPFTarget() {
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// Register the target.
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RegisterTargetMachine<BPFTargetMachine> X(getTheBPFleTarget());
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RegisterTargetMachine<BPFTargetMachine> Y(getTheBPFbeTarget());
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RegisterTargetMachine<BPFTargetMachine> Z(getTheBPFTarget());
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PassRegistry &PR = *PassRegistry::getPassRegistry();
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initializeBPFAbstractMemberAccessPass(PR);
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initializeBPFPreserveDITypePass(PR);
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initializeBPFMIPeepholePass(PR);
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initializeBPFMIPeepholeTruncElimPass(PR);
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}
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// DataLayout: little or big endian
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static std::string computeDataLayout(const Triple &TT) {
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if (TT.getArch() == Triple::bpfeb)
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return "E-m:e-p:64:64-i64:64-i128:128-n32:64-S128";
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else
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return "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128";
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}
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static Reloc::Model getEffectiveRelocModel(Optional<Reloc::Model> RM) {
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if (!RM.hasValue())
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return Reloc::PIC_;
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return *RM;
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}
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BPFTargetMachine::BPFTargetMachine(const Target &T, const Triple &TT,
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StringRef CPU, StringRef FS,
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const TargetOptions &Options,
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Optional<Reloc::Model> RM,
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Optional<CodeModel::Model> CM,
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CodeGenOpt::Level OL, bool JIT)
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: LLVMTargetMachine(T, computeDataLayout(TT), TT, CPU, FS, Options,
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getEffectiveRelocModel(RM),
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getEffectiveCodeModel(CM, CodeModel::Small), OL),
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TLOF(std::make_unique<TargetLoweringObjectFileELF>()),
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Subtarget(TT, std::string(CPU), std::string(FS), *this) {
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initAsmInfo();
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BPFMCAsmInfo *MAI =
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static_cast<BPFMCAsmInfo *>(const_cast<MCAsmInfo *>(AsmInfo.get()));
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MAI->setDwarfUsesRelocationsAcrossSections(!Subtarget.getUseDwarfRIS());
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}
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namespace {
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// BPF Code Generator Pass Configuration Options.
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class BPFPassConfig : public TargetPassConfig {
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public:
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BPFPassConfig(BPFTargetMachine &TM, PassManagerBase &PM)
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: TargetPassConfig(TM, PM) {}
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BPFTargetMachine &getBPFTargetMachine() const {
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return getTM<BPFTargetMachine>();
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}
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void addIRPasses() override;
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bool addInstSelector() override;
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void addMachineSSAOptimization() override;
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void addPreEmitPass() override;
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};
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}
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TargetPassConfig *BPFTargetMachine::createPassConfig(PassManagerBase &PM) {
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return new BPFPassConfig(*this, PM);
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}
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void BPFPassConfig::addIRPasses() {
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addPass(createBPFAbstractMemberAccess(&getBPFTargetMachine()));
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addPass(createBPFPreserveDIType());
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TargetPassConfig::addIRPasses();
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}
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// Install an instruction selector pass using
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// the ISelDag to gen BPF code.
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bool BPFPassConfig::addInstSelector() {
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addPass(createBPFISelDag(getBPFTargetMachine()));
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return false;
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}
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void BPFPassConfig::addMachineSSAOptimization() {
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addPass(createBPFMISimplifyPatchablePass());
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// The default implementation must be called first as we want eBPF
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// Peephole ran at last.
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TargetPassConfig::addMachineSSAOptimization();
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const BPFSubtarget *Subtarget = getBPFTargetMachine().getSubtargetImpl();
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if (!DisableMIPeephole) {
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if (Subtarget->getHasAlu32())
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addPass(createBPFMIPeepholePass());
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addPass(createBPFMIPeepholeTruncElimPass());
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}
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}
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void BPFPassConfig::addPreEmitPass() {
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addPass(createBPFMIPreEmitCheckingPass());
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if (getOptLevel() != CodeGenOpt::None)
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if (!DisableMIPeephole)
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addPass(createBPFMIPreEmitPeepholePass());
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}
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