From 156f6cafc28777dc06515114b4c81fef01ac7d43 Mon Sep 17 00:00:00 2001 From: Dean Michael Berris Date: Tue, 18 Oct 2016 05:54:15 +0000 Subject: [PATCH] [XRay] Support for for tail calls for ARM no-Thumb This patch adds simplified support for tail calls on ARM with XRay instrumentation. Known issue: compiled with generic flags: `-O3 -g -fxray-instrument -Wall -std=c++14 -ffunction-sections -fdata-sections` (this list doesn't include my specific flags like --target=armv7-linux-gnueabihf etc.), the following program #include #include #include [[clang::xray_always_instrument]] void __attribute__ ((noinline)) fC() { std::printf("In fC()\n"); } [[clang::xray_always_instrument]] void __attribute__ ((noinline)) fB() { std::printf("In fB()\n"); fC(); } [[clang::xray_always_instrument]] void __attribute__ ((noinline)) fA() { std::printf("In fA()\n"); fB(); } // Avoid infinite recursion in case the logging function is instrumented (so calls logging // function again). [[clang::xray_never_instrument]] void simplyPrint(int32_t functionId, XRayEntryType xret) { printf("XRay: functionId=%d type=%d.\n", int(functionId), int(xret)); } int main(int argc, char* argv[]) { __xray_set_handler(simplyPrint); printf("Patching...\n"); __xray_patch(); fA(); printf("Unpatching...\n"); __xray_unpatch(); fA(); return 0; } gives the following output: Patching... XRay: functionId=3 type=0. In fA() XRay: functionId=3 type=1. XRay: functionId=2 type=0. In fB() XRay: functionId=2 type=1. XRay: functionId=1 type=0. XRay: functionId=1 type=1. In fC() Unpatching... In fA() In fB() In fC() So for function fC() the exit sled seems to be called too much before function exit: before printing In fC(). Debugging shows that the above happens because printf from fC is also called as a tail call. So first the exit sled of fC is executed, and only then printf is jumped into. So it seems we can't do anything about this with the current approach (i.e. within the simplification described in https://reviews.llvm.org/D23988 ). Differential Revision: https://reviews.llvm.org/D25030 llvm-svn: 284456 --- llvm/lib/CodeGen/XRayInstrumentation.cpp | 13 +++-- llvm/lib/Target/ARM/ARMAsmPrinter.cpp | 3 ++ llvm/lib/Target/ARM/ARMAsmPrinter.h | 1 + llvm/lib/Target/ARM/ARMMCInstLower.cpp | 5 ++ llvm/test/CodeGen/ARM/xray-tail-call-sled.ll | 53 ++++++++++++++++++++ 5 files changed, 72 insertions(+), 3 deletions(-) create mode 100644 llvm/test/CodeGen/ARM/xray-tail-call-sled.ll diff --git a/llvm/lib/CodeGen/XRayInstrumentation.cpp b/llvm/lib/CodeGen/XRayInstrumentation.cpp index 7a3ca9799bb9..e76bf6948cff 100644 --- a/llvm/lib/CodeGen/XRayInstrumentation.cpp +++ b/llvm/lib/CodeGen/XRayInstrumentation.cpp @@ -95,10 +95,17 @@ void XRayInstrumentation::prependRetWithPatchableExit(MachineFunction &MF, { for (auto &MBB : MF) { for (auto &T : MBB.terminators()) { + unsigned Opc = 0; if (T.isReturn()) { - // Prepend the return instruction with PATCHABLE_FUNCTION_EXIT - BuildMI(MBB, T, T.getDebugLoc(), - TII->get(TargetOpcode::PATCHABLE_FUNCTION_EXIT)); + Opc = TargetOpcode::PATCHABLE_FUNCTION_EXIT; + } + if (TII->isTailCall(T)) { + Opc = TargetOpcode::PATCHABLE_TAIL_CALL; + } + if (Opc != 0) { + // Prepend the return instruction with PATCHABLE_FUNCTION_EXIT or + // PATCHABLE_TAIL_CALL . + BuildMI(MBB, T, T.getDebugLoc(),TII->get(Opc)); } } } diff --git a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp index bd95c33fc495..ad8a6ed0b6d1 100644 --- a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp +++ b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp @@ -2050,6 +2050,9 @@ void ARMAsmPrinter::EmitInstruction(const MachineInstr *MI) { case ARM::PATCHABLE_FUNCTION_EXIT: LowerPATCHABLE_FUNCTION_EXIT(*MI); return; + case ARM::PATCHABLE_TAIL_CALL: + LowerPATCHABLE_TAIL_CALL(*MI); + return; } MCInst TmpInst; diff --git a/llvm/lib/Target/ARM/ARMAsmPrinter.h b/llvm/lib/Target/ARM/ARMAsmPrinter.h index 277f725fc774..79269df2ae36 100644 --- a/llvm/lib/Target/ARM/ARMAsmPrinter.h +++ b/llvm/lib/Target/ARM/ARMAsmPrinter.h @@ -112,6 +112,7 @@ public: // XRay-specific lowering for ARM. void LowerPATCHABLE_FUNCTION_ENTER(const MachineInstr &MI); void LowerPATCHABLE_FUNCTION_EXIT(const MachineInstr &MI); + void LowerPATCHABLE_TAIL_CALL(const MachineInstr &MI); // Helper function that emits the XRay sleds we've collected for a particular // function. void EmitXRayTable(); diff --git a/llvm/lib/Target/ARM/ARMMCInstLower.cpp b/llvm/lib/Target/ARM/ARMMCInstLower.cpp index 19c91510c259..79f61652d61c 100644 --- a/llvm/lib/Target/ARM/ARMMCInstLower.cpp +++ b/llvm/lib/Target/ARM/ARMMCInstLower.cpp @@ -219,6 +219,11 @@ void ARMAsmPrinter::LowerPATCHABLE_FUNCTION_EXIT(const MachineInstr &MI) EmitSled(MI, SledKind::FUNCTION_EXIT); } +void ARMAsmPrinter::LowerPATCHABLE_TAIL_CALL(const MachineInstr &MI) +{ + EmitSled(MI, SledKind::TAIL_CALL); +} + void ARMAsmPrinter::EmitXRayTable() { if (Sleds.empty()) diff --git a/llvm/test/CodeGen/ARM/xray-tail-call-sled.ll b/llvm/test/CodeGen/ARM/xray-tail-call-sled.ll new file mode 100644 index 000000000000..d62a3b78662a --- /dev/null +++ b/llvm/test/CodeGen/ARM/xray-tail-call-sled.ll @@ -0,0 +1,53 @@ +; RUN: llc -filetype=asm -o - -mtriple=armv7-unknown-linux-gnu < %s | FileCheck %s + +define i32 @callee() nounwind noinline uwtable "function-instrument"="xray-always" { +; CHECK: .p2align 2 +; CHECK-LABEL: Lxray_sled_0: +; CHECK-NEXT: b #20 +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-LABEL: Ltmp0: + ret i32 0 +; CHECK-NEXT: mov r0, #0 +; CHECK-NEXT: .p2align 2 +; CHECK-LABEL: Lxray_sled_1: +; CHECK-NEXT: b #20 +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-LABEL: Ltmp1: +; CHECK-NEXT: bx lr +} + +define i32 @caller() nounwind noinline uwtable "function-instrument"="xray-always" { +; CHECK: .p2align 2 +; CHECK-LABEL: Lxray_sled_2: +; CHECK-NEXT: b #20 +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-LABEL: Ltmp2: +; CHECK: .p2align 2 +; CHECK-LABEL: Lxray_sled_3: +; CHECK-NEXT: b #20 +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-NEXT: nop +; CHECK-LABEL: Ltmp3: + %retval = tail call i32 @callee() +; CHECK: b callee + ret i32 %retval +} -- 2.34.1