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8135e49e9b
Currently, BPF has XADD (locked add) insn support and the asm looks like: lock *(u32 *)(r1 + 0) += r2 lock *(u64 *)(r1 + 0) += r2 The instruction itself does not have a return value. At the source code level, users often use __sync_fetch_and_add() which eventually translates to XADD. The return value of __sync_fetch_and_add() is supposed to be the old value in the xadd memory location. Since BPF::XADD insn does not support such a return value, this patch added a PreEmit phase to check such a usage. If such an illegal usage pattern is detected, a fatal error will be reported like line 4: Invalid usage of the XADD return value if compiled with -g, or Invalid usage of the XADD return value if compiled without -g. Signed-off-by: Yonghong Song <yhs@fb.com> Acked-by: Alexei Starovoitov <ast@kernel.org> git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342692 91177308-0d34-0410-b5e6-96231b3b80d8
97 lines
2.7 KiB
C++
97 lines
2.7 KiB
C++
//===-------------- BPFMIChecking.cpp - MI Checking Legality -------------===//
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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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//
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// This pass performs checking to signal errors for certain illegal usages at
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// MachineInstruction layer. Specially, the result of XADD{32,64} insn should
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// not be used. The pass is done at the PreEmit pass right before the
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// machine code is emitted at which point the register liveness information
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// is still available.
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//
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//===----------------------------------------------------------------------===//
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#include "BPF.h"
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#include "BPFInstrInfo.h"
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#include "BPFTargetMachine.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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using namespace llvm;
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#define DEBUG_TYPE "bpf-mi-checking"
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namespace {
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struct BPFMIPreEmitChecking : public MachineFunctionPass {
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static char ID;
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MachineFunction *MF;
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const TargetRegisterInfo *TRI;
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BPFMIPreEmitChecking() : MachineFunctionPass(ID) {
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initializeBPFMIPreEmitCheckingPass(*PassRegistry::getPassRegistry());
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}
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private:
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// Initialize class variables.
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void initialize(MachineFunction &MFParm);
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void checkingIllegalXADD(void);
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public:
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// Main entry point for this pass.
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bool runOnMachineFunction(MachineFunction &MF) override {
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if (!skipFunction(MF.getFunction())) {
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initialize(MF);
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checkingIllegalXADD();
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}
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return false;
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}
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};
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// Initialize class variables.
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void BPFMIPreEmitChecking::initialize(MachineFunction &MFParm) {
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MF = &MFParm;
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TRI = MF->getSubtarget<BPFSubtarget>().getRegisterInfo();
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LLVM_DEBUG(dbgs() << "*** BPF PreEmit checking pass ***\n\n");
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}
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void BPFMIPreEmitChecking::checkingIllegalXADD(void) {
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for (MachineBasicBlock &MBB : *MF) {
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for (MachineInstr &MI : MBB) {
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if (MI.getOpcode() != BPF::XADD32 && MI.getOpcode() != BPF::XADD64)
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continue;
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LLVM_DEBUG(MI.dump());
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if (!MI.allDefsAreDead()) {
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DebugLoc Empty;
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const DebugLoc &DL = MI.getDebugLoc();
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if (DL != Empty)
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report_fatal_error("line " + std::to_string(DL.getLine()) +
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": Invalid usage of the XADD return value", false);
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else
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report_fatal_error("Invalid usage of the XADD return value", false);
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}
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}
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}
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return;
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}
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} // end default namespace
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INITIALIZE_PASS(BPFMIPreEmitChecking, "bpf-mi-pemit-checking",
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"BPF PreEmit Checking", false, false)
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char BPFMIPreEmitChecking::ID = 0;
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FunctionPass* llvm::createBPFMIPreEmitCheckingPass()
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{
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return new BPFMIPreEmitChecking();
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}
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