1 //===- XRayInstrumentation.cpp - Adds XRay instrumentation to functions. --===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // This file implements a MachineFunctionPass that inserts the appropriate
10 // XRay instrumentation instructions. We look for XRay-specific attributes
11 // on the function to determine whether we should insert the replacement
14 //===---------------------------------------------------------------------===//
63   // Replace the original RET instruction with the exit sled code ("patchable
64   //   ret" pseudo-instruction), so that at runtime XRay can replace the sled
65   //   with a code jumping to XRay trampoline, which calls the tracing handler
66   //   and, in the end, issues the RET instruction.
67   // This is the approach to go on CPUs which have a single RET instruction,
73   // Prepend the original return instruction with the exit sled code ("patchable
74   //   function exit" pseudo-instruction), preserving the original return
75   //   instruction just after the exit sled code.
76   // This is the approach to go on CPUs which have multiple options for the
77   //   return instruction, like ARM. For such CPUs we can't just jump into the
79   //   have to call the trampoline and return from it to the original return
80   //   instruction of the function being instrumented.
98           (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {  in replaceRetWithPatchableRet()
103       if (TII->isTailCall(T) && op.HandleTailcall) {  in replaceRetWithPatchableRet()
104         // Treat the tail call as a return instruction, which has a  in replaceRetWithPatchableRet()
105         // different-looking sled than the normal return case.  in replaceRetWithPatchableRet()
109         auto MIB = BuildMI(MBB, T, T.getDebugLoc(), TII->get(Opc))  in replaceRetWithPatchableRet()
121     I->eraseFromParent();  in replaceRetWithPatchableRet()
131           (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {  in prependRetWithPatchableExit()
134       if (TII->isTailCall(T) && op.HandleTailcall) {  in prependRetWithPatchableExit()
138         // Prepend the return instruction with PATCHABLE_FUNCTION_EXIT or  in prependRetWithPatchableExit()
140         BuildMI(MBB, T, T.getDebugLoc(), TII->get(Opc));  in prependRetWithPatchableExit()
147   auto InstrAttr = F.getFnAttribute("function-instrument");  in runOnMachineFunction()
149                           InstrAttr.getValueAsString() == "xray-always";  in runOnMachineFunction()
151                          InstrAttr.getValueAsString() == "xray-never";  in runOnMachineFunction()
154   auto IgnoreLoopsAttr = F.getFnAttribute("xray-ignore-loops");  in runOnMachineFunction()
160         "xray-instruction-threshold", std::numeric_limits<uint64_t>::max());  in runOnMachineFunction()
164     // Count the number of MachineInstr`s in MachineFunction  in runOnMachineFunction()
172       // Get MachineDominatorTree or compute it on the fly if it's unavailable  in runOnMachineFunction()
175       auto *MDT = MDTWrapper ? &MDTWrapper->getDomTree() : nullptr;  in runOnMachineFunction()
182       // Get MachineLoopInfo or compute it on the fly if it's unavailable  in runOnMachineFunction()
184       auto *MLI = MLIWrapper ? &MLIWrapper->getLI() : nullptr;  in runOnMachineFunction()
187         ComputedMLI.analyze(MDT->getBase());  in runOnMachineFunction()
192       // FIXME: Maybe make this smarter, and see whether the loops are dependent  in runOnMachineFunction()
193       // on inputs or side-effects?  in runOnMachineFunction()
194       if (MLI->empty() && TooFewInstrs)  in runOnMachineFunction()
202   // We look for the first non-empty MachineBasicBlock, so that we can insert  in runOnMachineFunction()
203   // the function instrumentation in the appropriate place.  in runOnMachineFunction()
207     return false; // The function is empty.  in runOnMachineFunction()
219   if (!F.hasFnAttribute("xray-skip-entry")) {  in runOnMachineFunction()
220     // First, insert an PATCHABLE_FUNCTION_ENTER as the first instruction of the  in runOnMachineFunction()
223             TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));  in runOnMachineFunction()
226   if (!F.hasFnAttribute("xray-skip-exit")) {  in runOnMachineFunction()
237       // For the architectures which don't have a single return instruction  in runOnMachineFunction()
253       // For the architectures that have a single return instruction (such as  in runOnMachineFunction()
254       //   RETQ on x86_64).  in runOnMachineFunction()
268 INITIALIZE_PASS_BEGIN(XRayInstrumentation, "xray-instrumentation",
271 INITIALIZE_PASS_END(XRayInstrumentation, "xray-instrumentation",