[llvm-branch-commits] [llvm] [AArch64][PAC] Support BLRA* instructions in SLS Hardening pass (PR #97605)
Anatoly Trosinenko via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Thu Jul 4 07:43:00 PDT 2024
https://github.com/atrosinenko updated https://github.com/llvm/llvm-project/pull/97605
>From f49c32c8465e9e68d7345fa82ae1294cc2faf0e7 Mon Sep 17 00:00:00 2001
From: Anatoly Trosinenko <atrosinenko at accesssoftek.com>
Date: Mon, 1 Jul 2024 20:13:54 +0300
Subject: [PATCH] [AArch64][PAC] Support BLRA* instructions in SLS Hardening
pass
Make SLS Hardening pass handle BLRA* instructions the same way it
handles BLR. The thunk names have the form
__llvm_slsblr_thunk_xN for BLR thunks
__llvm_slsblr_thunk_(aaz|abz)_xN for BLRAAZ and BLRABZ thunks
__llvm_slsblr_thunk_(aa|ab)_xN_xM for BLRAA and BLRAB thunks
Now there are about 1800 possible thunk names, so do not rely on linear
thunk function's name lookup and parse the name instead.
---
.../Target/AArch64/AArch64SLSHardening.cpp | 326 ++++++++++++------
.../speculation-hardening-sls-blra.mir | 210 +++++++++++
2 files changed, 432 insertions(+), 104 deletions(-)
create mode 100644 llvm/test/CodeGen/AArch64/speculation-hardening-sls-blra.mir
diff --git a/llvm/lib/Target/AArch64/AArch64SLSHardening.cpp b/llvm/lib/Target/AArch64/AArch64SLSHardening.cpp
index 24f023a3d70e7..4ae2e48af337f 100644
--- a/llvm/lib/Target/AArch64/AArch64SLSHardening.cpp
+++ b/llvm/lib/Target/AArch64/AArch64SLSHardening.cpp
@@ -13,6 +13,7 @@
#include "AArch64InstrInfo.h"
#include "AArch64Subtarget.h"
+#include "llvm/ADT/StringSwitch.h"
#include "llvm/CodeGen/IndirectThunks.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
@@ -23,6 +24,7 @@
#include "llvm/IR/DebugLoc.h"
#include "llvm/Pass.h"
#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FormatVariadic.h"
#include "llvm/Target/TargetMachine.h"
#include <cassert>
@@ -32,17 +34,103 @@ using namespace llvm;
#define AARCH64_SLS_HARDENING_NAME "AArch64 sls hardening pass"
-static const char SLSBLRNamePrefix[] = "__llvm_slsblr_thunk_";
+// Common name prefix of all thunks generated by this pass.
+//
+// The generic form is
+// __llvm_slsblr_thunk_xN for BLR thunks
+// __llvm_slsblr_thunk_(aaz|abz)_xN for BLRAAZ and BLRABZ thunks
+// __llvm_slsblr_thunk_(aa|ab)_xN_xM for BLRAA and BLRAB thunks
+static constexpr StringRef CommonNamePrefix = "__llvm_slsblr_thunk_";
namespace {
-// Set of inserted thunks: bitmask with bits corresponding to
-// indexes in SLSBLRThunks array.
-typedef uint32_t ThunksSet;
+struct ThunkKind {
+ enum ThunkKindId {
+ ThunkBR,
+ ThunkBRAA,
+ ThunkBRAB,
+ ThunkBRAAZ,
+ ThunkBRABZ,
+ };
+
+ ThunkKindId Id;
+ StringRef NameInfix;
+ bool HasXmOperand;
+ bool NeedsPAuth;
+
+ // Opcode to perform indirect jump from inside the thunk.
+ unsigned BROpcode;
+
+ static const ThunkKind BR;
+ static const ThunkKind BRAA;
+ static const ThunkKind BRAB;
+ static const ThunkKind BRAAZ;
+ static const ThunkKind BRABZ;
+};
+
+// Set of inserted thunks.
+class ThunksSet {
+public:
+ static constexpr unsigned NumXRegisters = 32;
+
+ // Given Xn register, returns n.
+ static unsigned indexOfXReg(Register Xn);
+ // Given n, returns Xn register.
+ static Register xRegByIndex(unsigned N);
+
+ ThunksSet &operator|=(const ThunksSet &Other) {
+ BLRThunks |= Other.BLRThunks;
+ BLRAAZThunks |= Other.BLRAAZThunks;
+ BLRABZThunks |= Other.BLRABZThunks;
+ for (unsigned I = 0; I < NumXRegisters; ++I)
+ BLRAAThunks[I] |= Other.BLRAAThunks[I];
+ for (unsigned I = 0; I < NumXRegisters; ++I)
+ BLRABThunks[I] |= Other.BLRABThunks[I];
+
+ return *this;
+ }
+
+ bool get(ThunkKind::ThunkKindId Kind, Register Xn, Register Xm) {
+ uint32_t XnBit = 1u << indexOfXReg(Xn);
+ return getBitmask(Kind, Xm) & XnBit;
+ }
+
+ void set(ThunkKind::ThunkKindId Kind, Register Xn, Register Xm) {
+ uint32_t XnBit = 1u << indexOfXReg(Xn);
+ getBitmask(Kind, Xm) |= XnBit;
+ }
+
+private:
+ // Bitmasks representing operands used, with n-th bit corresponding to Xn
+ // register operand. If the instruction has a second operand (Xm), an array
+ // of bitmasks is used, indexed by m.
+ // Indexes corresponding to the forbidden x16, x17 and x30 registers are
+ // always unset, for simplicity there are no holes.
+ uint32_t BLRThunks = 0;
+ uint32_t BLRAAZThunks = 0;
+ uint32_t BLRABZThunks = 0;
+ uint32_t BLRAAThunks[NumXRegisters] = {};
+ uint32_t BLRABThunks[NumXRegisters] = {};
+
+ uint32_t &getBitmask(ThunkKind::ThunkKindId Kind, Register Xm) {
+ switch (Kind) {
+ case ThunkKind::ThunkBR:
+ return BLRThunks;
+ case ThunkKind::ThunkBRAAZ:
+ return BLRAAZThunks;
+ case ThunkKind::ThunkBRABZ:
+ return BLRABZThunks;
+ case ThunkKind::ThunkBRAA:
+ return BLRAAThunks[indexOfXReg(Xm)];
+ case ThunkKind::ThunkBRAB:
+ return BLRABThunks[indexOfXReg(Xm)];
+ }
+ }
+};
struct SLSHardeningInserter : ThunkInserter<SLSHardeningInserter, ThunksSet> {
public:
- const char *getThunkPrefix() { return SLSBLRNamePrefix; }
+ const char *getThunkPrefix() { return CommonNamePrefix.data(); }
bool mayUseThunk(const MachineFunction &MF) {
ComdatThunks &= !MF.getSubtarget<AArch64Subtarget>().hardenSlsNoComdat();
// We are inserting barriers aside from thunk calls, so
@@ -68,6 +156,57 @@ struct SLSHardeningInserter : ThunkInserter<SLSHardeningInserter, ThunksSet> {
} // end anonymous namespace
+const ThunkKind ThunkKind::BR = {ThunkBR, "", false, false, AArch64::BR};
+const ThunkKind ThunkKind::BRAA = {ThunkBRAA, "aa_", true, true, AArch64::BRAA};
+const ThunkKind ThunkKind::BRAB = {ThunkBRAB, "ab_", true, true, AArch64::BRAB};
+const ThunkKind ThunkKind::BRAAZ = {ThunkBRAAZ, "aaz_", false, true,
+ AArch64::BRAAZ};
+const ThunkKind ThunkKind::BRABZ = {ThunkBRABZ, "abz_", false, true,
+ AArch64::BRABZ};
+
+static const ThunkKind *getThunkKind(unsigned OriginalOpcode) {
+ switch (OriginalOpcode) {
+ case AArch64::BLR:
+ case AArch64::BLRNoIP:
+ return &ThunkKind::BR;
+ case AArch64::BLRAA:
+ return &ThunkKind::BRAA;
+ case AArch64::BLRAB:
+ return &ThunkKind::BRAB;
+ case AArch64::BLRAAZ:
+ return &ThunkKind::BRAAZ;
+ case AArch64::BLRABZ:
+ return &ThunkKind::BRABZ;
+ }
+ return nullptr;
+}
+
+static bool isBLR(const MachineInstr &MI) {
+ return getThunkKind(MI.getOpcode()) != nullptr;
+}
+
+unsigned ThunksSet::indexOfXReg(Register Reg) {
+ assert(AArch64::GPR64RegClass.contains(Reg));
+ assert(Reg != AArch64::X16 && Reg != AArch64::X17 && Reg != AArch64::LR);
+
+ // Most Xn registers have consequent ids, except for FP and XZR.
+ unsigned Result = (unsigned)Reg - (unsigned)AArch64::X0;
+ if (Reg == AArch64::FP)
+ Result = 29;
+ else if (Reg == AArch64::XZR)
+ Result = 31;
+
+ assert(Result < NumXRegisters && "Internal register numbering changed");
+ assert(AArch64::GPR64RegClass.getRegister(Result).id() == Reg &&
+ "Internal register numbering changed");
+
+ return Result;
+}
+
+Register ThunksSet::xRegByIndex(unsigned N) {
+ return AArch64::GPR64RegClass.getRegister(N);
+}
+
static void insertSpeculationBarrier(const AArch64Subtarget *ST,
MachineBasicBlock &MBB,
MachineBasicBlock::iterator MBBI,
@@ -104,22 +243,6 @@ ThunksSet SLSHardeningInserter::insertThunks(MachineModuleInfo &MMI,
return ExistingThunks;
}
-static bool isBLR(const MachineInstr &MI) {
- switch (MI.getOpcode()) {
- case AArch64::BLR:
- case AArch64::BLRNoIP:
- return true;
- case AArch64::BLRAA:
- case AArch64::BLRAB:
- case AArch64::BLRAAZ:
- case AArch64::BLRABZ:
- llvm_unreachable("Currently, LLVM's code generator does not support "
- "producing BLRA* instructions. Therefore, there's no "
- "support in this pass for those instructions.");
- }
- return false;
-}
-
bool SLSHardeningInserter::hardenReturnsAndBRs(MachineModuleInfo &MMI,
MachineBasicBlock &MBB) {
const AArch64Subtarget *ST =
@@ -139,52 +262,49 @@ bool SLSHardeningInserter::hardenReturnsAndBRs(MachineModuleInfo &MMI,
return Modified;
}
-static const unsigned NumPermittedRegs = 29;
-static const struct ThunkNameAndReg {
- const char* Name;
- Register Reg;
-} SLSBLRThunks[NumPermittedRegs] = {
- { "__llvm_slsblr_thunk_x0", AArch64::X0},
- { "__llvm_slsblr_thunk_x1", AArch64::X1},
- { "__llvm_slsblr_thunk_x2", AArch64::X2},
- { "__llvm_slsblr_thunk_x3", AArch64::X3},
- { "__llvm_slsblr_thunk_x4", AArch64::X4},
- { "__llvm_slsblr_thunk_x5", AArch64::X5},
- { "__llvm_slsblr_thunk_x6", AArch64::X6},
- { "__llvm_slsblr_thunk_x7", AArch64::X7},
- { "__llvm_slsblr_thunk_x8", AArch64::X8},
- { "__llvm_slsblr_thunk_x9", AArch64::X9},
- { "__llvm_slsblr_thunk_x10", AArch64::X10},
- { "__llvm_slsblr_thunk_x11", AArch64::X11},
- { "__llvm_slsblr_thunk_x12", AArch64::X12},
- { "__llvm_slsblr_thunk_x13", AArch64::X13},
- { "__llvm_slsblr_thunk_x14", AArch64::X14},
- { "__llvm_slsblr_thunk_x15", AArch64::X15},
- // X16 and X17 are deliberately missing, as the mitigation requires those
- // register to not be used in BLR. See comment in ConvertBLRToBL for more
- // details.
- { "__llvm_slsblr_thunk_x18", AArch64::X18},
- { "__llvm_slsblr_thunk_x19", AArch64::X19},
- { "__llvm_slsblr_thunk_x20", AArch64::X20},
- { "__llvm_slsblr_thunk_x21", AArch64::X21},
- { "__llvm_slsblr_thunk_x22", AArch64::X22},
- { "__llvm_slsblr_thunk_x23", AArch64::X23},
- { "__llvm_slsblr_thunk_x24", AArch64::X24},
- { "__llvm_slsblr_thunk_x25", AArch64::X25},
- { "__llvm_slsblr_thunk_x26", AArch64::X26},
- { "__llvm_slsblr_thunk_x27", AArch64::X27},
- { "__llvm_slsblr_thunk_x28", AArch64::X28},
- { "__llvm_slsblr_thunk_x29", AArch64::FP},
- // X30 is deliberately missing, for similar reasons as X16 and X17 are
- // missing.
- { "__llvm_slsblr_thunk_x31", AArch64::XZR},
-};
+static SmallString<32> createThunkName(const ThunkKind &Kind, Register Xn,
+ Register Xm) {
+ unsigned N = ThunksSet::indexOfXReg(Xn);
+ if (!Kind.HasXmOperand)
+ return formatv("{0}{1}x{2}", CommonNamePrefix, Kind.NameInfix, N);
+
+ unsigned M = ThunksSet::indexOfXReg(Xm);
+ return formatv("{0}{1}x{2}_x{3}", CommonNamePrefix, Kind.NameInfix, N, M);
+}
-unsigned getThunkIndex(Register Reg) {
- for (unsigned I = 0; I < NumPermittedRegs; ++I)
- if (SLSBLRThunks[I].Reg == Reg)
- return I;
- llvm_unreachable("Unexpected register");
+static const ThunkKind &parseThunkName(StringRef ThunkName, Register &Xn,
+ Register &Xm) {
+ assert(ThunkName.starts_with(CommonNamePrefix) &&
+ "Should be filtered out by ThunkInserter");
+ // Thunk name suffix, such as "x1" or "aa_x2_x3".
+ StringRef NameSuffix = ThunkName.drop_front(CommonNamePrefix.size());
+
+ // Parse thunk kind based on thunk name infix.
+ const ThunkKind &Kind = *StringSwitch<const ThunkKind *>(NameSuffix)
+ .StartsWith("aa_", &ThunkKind::BRAA)
+ .StartsWith("ab_", &ThunkKind::BRAB)
+ .StartsWith("aaz_", &ThunkKind::BRAAZ)
+ .StartsWith("abz_", &ThunkKind::BRABZ)
+ .Default(&ThunkKind::BR);
+
+ auto ParseRegName = [](StringRef Name) {
+ assert(Name.starts_with("x") && "xN register name expected");
+ unsigned N;
+ bool Fail = Name.drop_front(1).getAsInteger(/*Radix=*/10, N);
+ assert(!Fail && N < 32 && "Unexpected register");
+ return ThunksSet::xRegByIndex(N);
+ };
+
+ // For example, "x1" or "x2_x3".
+ StringRef RegsStr = NameSuffix.drop_front(Kind.NameInfix.size());
+ StringRef XnStr, XmStr;
+ std::tie(XnStr, XmStr) = RegsStr.split('_');
+
+ // Parse register operands.
+ Xn = ParseRegName(XnStr);
+ Xm = Kind.HasXmOperand ? ParseRegName(XmStr) : AArch64::NoRegister;
+
+ return Kind;
}
void SLSHardeningInserter::populateThunk(MachineFunction &MF) {
@@ -192,11 +312,8 @@ void SLSHardeningInserter::populateThunk(MachineFunction &MF) {
"ComdatThunks value changed since MF creation");
// FIXME: How to better communicate Register number, rather than through
// name and lookup table?
- assert(MF.getName().starts_with(getThunkPrefix()));
- auto ThunkIt = llvm::find_if(
- SLSBLRThunks, [&MF](auto T) { return T.Name == MF.getName(); });
- assert(ThunkIt != std::end(SLSBLRThunks));
- Register ThunkReg = ThunkIt->Reg;
+ Register Xn, Xm;
+ const ThunkKind &Kind = parseThunkName(MF.getName(), Xn, Xm);
const TargetInstrInfo *TII =
MF.getSubtarget<AArch64Subtarget>().getInstrInfo();
@@ -221,13 +338,19 @@ void SLSHardeningInserter::populateThunk(MachineFunction &MF) {
// __llvm_slsblr_thunk_xN:
// BR xN
// barrierInsts
- Entry->addLiveIn(ThunkReg);
- // MOV X16, ThunkReg == ORR X16, XZR, ThunkReg, LSL #0
+ Entry->addLiveIn(Xn);
+ // MOV X16, Reg == ORR X16, XZR, Reg, LSL #0
BuildMI(Entry, DebugLoc(), TII->get(AArch64::ORRXrs), AArch64::X16)
.addReg(AArch64::XZR)
- .addReg(ThunkReg)
+ .addReg(Xn)
.addImm(0);
- BuildMI(Entry, DebugLoc(), TII->get(AArch64::BR)).addReg(AArch64::X16);
+ auto &Builder =
+ BuildMI(Entry, DebugLoc(), TII->get(Kind.BROpcode)).addReg(AArch64::X16);
+ if (Xm != AArch64::NoRegister) {
+ Entry->addLiveIn(Xm);
+ Builder.addReg(Xm);
+ }
+
// Make sure the thunks do not make use of the SB extension in case there is
// a function somewhere that will call to it that for some reason disabled
// the SB extension locally on that function, even though it's enabled for
@@ -274,40 +397,31 @@ void SLSHardeningInserter::convertBLRToBL(
MachineInstr &BLR = *MBBI;
assert(isBLR(BLR));
- unsigned BLOpcode;
- Register Reg;
- bool RegIsKilled;
- switch (BLR.getOpcode()) {
- case AArch64::BLR:
- case AArch64::BLRNoIP:
- BLOpcode = AArch64::BL;
- Reg = BLR.getOperand(0).getReg();
- assert(Reg != AArch64::X16 && Reg != AArch64::X17 && Reg != AArch64::LR);
- RegIsKilled = BLR.getOperand(0).isKill();
- break;
- case AArch64::BLRAA:
- case AArch64::BLRAB:
- case AArch64::BLRAAZ:
- case AArch64::BLRABZ:
- llvm_unreachable("BLRA instructions cannot yet be produced by LLVM, "
- "therefore there is no need to support them for now.");
- default:
- llvm_unreachable("unhandled BLR");
- }
+ const ThunkKind &Kind = *getThunkKind(BLR.getOpcode());
+
+ unsigned NumRegOperands = Kind.HasXmOperand ? 2 : 1;
+ assert(BLR.getNumExplicitOperands() == NumRegOperands &&
+ "Expected one or two register inputs");
+ Register Xn = BLR.getOperand(0).getReg();
+ Register Xm =
+ Kind.HasXmOperand ? BLR.getOperand(1).getReg() : AArch64::NoRegister;
+
DebugLoc DL = BLR.getDebugLoc();
MachineFunction &MF = *MBBI->getMF();
MCContext &Context = MBB.getParent()->getContext();
const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
- unsigned ThunkIndex = getThunkIndex(Reg);
- StringRef ThunkName = SLSBLRThunks[ThunkIndex].Name;
+
+ auto ThunkName = createThunkName(Kind, Xn, Xm);
MCSymbol *Sym = Context.getOrCreateSymbol(ThunkName);
- if (!(Thunks & (1u << ThunkIndex))) {
- Thunks |= 1u << ThunkIndex;
- createThunkFunction(MMI, ThunkName, ComdatThunks);
+
+ if (!Thunks.get(Kind.Id, Xn, Xm)) {
+ StringRef TargetAttrs = Kind.NeedsPAuth ? "+pauth" : "";
+ Thunks.set(Kind.Id, Xn, Xm);
+ createThunkFunction(MMI, ThunkName, ComdatThunks, TargetAttrs);
}
- MachineInstr *BL = BuildMI(MBB, MBBI, DL, TII->get(BLOpcode)).addSym(Sym);
+ MachineInstr *BL = BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL)).addSym(Sym);
// Now copy the implicit operands from BLR to BL and copy other necessary
// info.
@@ -338,9 +452,13 @@ void SLSHardeningInserter::convertBLRToBL(
// Now copy over the implicit operands from the original BLR
BL->copyImplicitOps(MF, BLR);
MF.moveCallSiteInfo(&BLR, BL);
- // Also add the register called in the BLR as being used in the called thunk.
- BL->addOperand(MachineOperand::CreateReg(Reg, false /*isDef*/, true /*isImp*/,
- RegIsKilled /*isKill*/));
+ // Also add the register operands of the original BLR* instruction
+ // as being used in the called thunk.
+ for (unsigned OpIdx = 0; OpIdx < NumRegOperands; ++OpIdx) {
+ MachineOperand &Op = BLR.getOperand(OpIdx);
+ BL->addOperand(MachineOperand::CreateReg(Op.getReg(), /*isDef=*/false,
+ /*isImp=*/true, Op.isKill()));
+ }
// Remove BLR instruction
MBB.erase(MBBI);
}
diff --git a/llvm/test/CodeGen/AArch64/speculation-hardening-sls-blra.mir b/llvm/test/CodeGen/AArch64/speculation-hardening-sls-blra.mir
new file mode 100644
index 0000000000000..bdeba53e25071
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/speculation-hardening-sls-blra.mir
@@ -0,0 +1,210 @@
+# RUN: llc -verify-machineinstrs -mtriple=aarch64-none-linux-gnu \
+# RUN: -start-before aarch64-sls-hardening -o - %s \
+# RUN: -asm-verbose=0 \
+# RUN: | FileCheck %s \
+# RUN: --implicit-check-not=__llvm_slsblr_thunk_aa_x5_x8 \
+# RUN: --implicit-check-not=__llvm_slsblr_thunk_ab_x5_x8 \
+# RUN: --implicit-check-not=__llvm_slsblr_thunk_aaz_x5 \
+# RUN: --implicit-check-not=__llvm_slsblr_thunk_abz_x5
+
+# Pointer Authentication extension introduces more branch-with-link instructions
+# for the BLR SLS hardening to handle, namely BLRAA, BLRAB, BLRAAZ and BLRABZ.
+# Unlike the non-authenticating BLR instruction, BLRAA and BLRAB accept two
+# register operands (almost 900 combinations for each instruction).
+# For that reason, it is not practical to create all possible thunks.
+
+# Check that the BLR SLS hardening transforms BLRA* instructions into
+# unconditional BL calls to the correct thunk functions.
+# Check that only relevant thunk functions are generated.
+--- |
+ define void @test_instructions() #0 {
+ entry:
+ ret void
+ }
+
+ define void @test_no_redef() #0 {
+ entry:
+ ret void
+ }
+
+ define void @test_regs() #0 {
+ entry:
+ ret void
+ }
+
+ attributes #0 = { "target-features"="+pauth,+harden-sls-blr" }
+...
+
+# Test that all BLRA* instructions are handled.
+---
+name: test_instructions
+tracksRegLiveness: true
+body: |
+ bb.0.entry:
+ liveins: $lr, $x0, $x1, $x2, $x3
+
+ BLRAA $x0, $x1, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAB $x1, $x2, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAAZ $x2, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRABZ $x3, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ RET undef $lr
+...
+
+# Test that the same thunk function is not created twice.
+---
+name: test_no_redef
+tracksRegLiveness: true
+body: |
+ bb.0.entry:
+ liveins: $lr, $x0, $x1, $x2, $x3, $x4
+
+ ; thunk used by @test_instructions
+ BLRAB $x1, $x2, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+
+ ; thunk used by this function twice
+ BLRAB $x3, $x4, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAB $x3, $x4, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+
+ RET undef $lr
+...
+
+# Test that all xN registers (except x16, x17, x30 and xzr) are handled.
+---
+name: test_regs
+tracksRegLiveness: true
+body: |
+ bb.0.entry:
+ liveins: $lr, $x0, $x1, $x2, $x3, $x4, $x5, $x6, $x7, $x8, $x9, $x10, $x11, $x12, $x13, $x14, $x15, $x16, $x17, $x18, $x19, $x20, $x21, $x22, $x23, $x24, $x25, $x26, $x27, $x28, $fp
+
+ BLRAA $x0, $x1, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x2, $x3, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x4, $x5, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x6, $x7, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x8, $x9, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x10, $x11, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x12, $x13, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x14, $x15, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ ; skipping x16 and x17
+ BLRAA $x18, $x19, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x20, $x21, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x22, $x23, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x24, $x25, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x26, $x27, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ BLRAA $x28, $fp, implicit-def $lr, implicit $sp, implicit-def $sp, implicit-def $w0
+ RET undef $lr
+...
+
+# CHECK-LABEL: test_instructions:
+# CHECK-NEXT: .cfi_startproc
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x0_x1
+# CHECK-NEXT: bl __llvm_slsblr_thunk_ab_x1_x2
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aaz_x2
+# CHECK-NEXT: bl __llvm_slsblr_thunk_abz_x3
+# CHECK-NEXT: ret
+
+# CHECK-LABEL: test_no_redef:
+# CHECK-NEXT: .cfi_startproc
+# CHECK-NEXT: bl __llvm_slsblr_thunk_ab_x1_x2
+# CHECK-NEXT: bl __llvm_slsblr_thunk_ab_x3_x4
+# CHECK-NEXT: bl __llvm_slsblr_thunk_ab_x3_x4
+# CHECK-NEXT: ret
+
+# CHECK-LABEL: test_regs:
+# CHECK-NEXT: .cfi_startproc
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x0_x1
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x2_x3
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x4_x5
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x6_x7
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x8_x9
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x10_x11
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x12_x13
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x14_x15
+# skipping x16 and x17
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x18_x19
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x20_x21
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x22_x23
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x24_x25
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x26_x27
+# CHECK-NEXT: bl __llvm_slsblr_thunk_aa_x28_x29
+# CHECK-NEXT: ret
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x0_x1:
+# CHECK-NEXT: mov x16, x0
+# CHECK-NEXT: braa x16, x1
+# CHECK-NEXT: dsb sy
+# CHECK-NEXT: isb
+
+# CHECK-LABEL: __llvm_slsblr_thunk_ab_x1_x2:
+# CHECK-NEXT: mov x16, x1
+# CHECK-NEXT: brab x16, x2
+# CHECK-NEXT: dsb sy
+# CHECK-NEXT: isb
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aaz_x2:
+# CHECK-NEXT: mov x16, x2
+# CHECK-NEXT: braaz x16
+# CHECK-NEXT: dsb sy
+# CHECK-NEXT: isb
+
+# CHECK-LABEL: __llvm_slsblr_thunk_abz_x3:
+# CHECK-NEXT: mov x16, x3
+# CHECK-NEXT: brabz x16
+# CHECK-NEXT: dsb sy
+# CHECK-NEXT: isb
+
+# The instruction *operands* should correspond to the thunk function *name*
+# (check that the name is parsed correctly when populating the thunk).
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x2_x3:
+# CHECK-NEXT: mov x16, x2
+# CHECK: braa x16, x3
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x4_x5:
+# CHECK-NEXT: mov x16, x4
+# CHECK: braa x16, x5
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x6_x7:
+# CHECK-NEXT: mov x16, x6
+# CHECK: braa x16, x7
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x8_x9:
+# CHECK-NEXT: mov x16, x8
+# CHECK: braa x16, x9
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x10_x11:
+# CHECK-NEXT: mov x16, x10
+# CHECK: braa x16, x11
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x12_x13:
+# CHECK-NEXT: mov x16, x12
+# CHECK: braa x16, x13
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x14_x15:
+# CHECK-NEXT: mov x16, x14
+# CHECK: braa x16, x15
+
+# skipping x16 and x17
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x18_x19:
+# CHECK-NEXT: mov x16, x18
+# CHECK: braa x16, x19
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x20_x21:
+# CHECK-NEXT: mov x16, x20
+# CHECK: braa x16, x21
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x22_x23:
+# CHECK-NEXT: mov x16, x22
+# CHECK: braa x16, x23
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x24_x25:
+# CHECK-NEXT: mov x16, x24
+# CHECK: braa x16, x25
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x26_x27:
+# CHECK-NEXT: mov x16, x26
+# CHECK: braa x16, x27
+
+# CHECK-LABEL: __llvm_slsblr_thunk_aa_x28_x29:
+# CHECK-NEXT: mov x16, x28
+# CHECK: braa x16, x29
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