[llvm] [BOLT][AArch64] Add support for long absolute LLD thunks/veneers (PR #113408)
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llvm-commits at lists.llvm.org
Tue Oct 22 20:05:31 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-bolt
Author: Maksim Panchenko (maksfb)
<details>
<summary>Changes</summary>
Absolute thunks generated by LLD reference function addresses recorded as data in code. Since they are generated by the linker, they don't have relocations associated with them and thus the addresses are left undetected. Use pattern matching to detect such thunks and handle them in VeneerElimination pass.
---
Full diff: https://github.com/llvm/llvm-project/pull/113408.diff
4 Files Affected:
- (modified) bolt/include/bolt/Core/MCPlusBuilder.h (+5)
- (modified) bolt/lib/Passes/VeneerElimination.cpp (+31-12)
- (modified) bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp (+64)
- (added) bolt/test/AArch64/veneer-lld-abs.s (+51)
``````````diff
diff --git a/bolt/include/bolt/Core/MCPlusBuilder.h b/bolt/include/bolt/Core/MCPlusBuilder.h
index 32eda0b283b883..b9a13968535a5c 100644
--- a/bolt/include/bolt/Core/MCPlusBuilder.h
+++ b/bolt/include/bolt/Core/MCPlusBuilder.h
@@ -1536,6 +1536,11 @@ class MCPlusBuilder {
llvm_unreachable("not implemented");
}
+ virtual bool matchAbsLongVeneer(const BinaryFunction &BF,
+ uint64_t &TargetAddress) const {
+ llvm_unreachable("not implemented");
+ }
+
virtual bool matchAdrpAddPair(const MCInst &Adrp, const MCInst &Add) const {
llvm_unreachable("not implemented");
return false;
diff --git a/bolt/lib/Passes/VeneerElimination.cpp b/bolt/lib/Passes/VeneerElimination.cpp
index 8bf0359477c658..2736448df50cc3 100644
--- a/bolt/lib/Passes/VeneerElimination.cpp
+++ b/bolt/lib/Passes/VeneerElimination.cpp
@@ -29,30 +29,49 @@ static llvm::cl::opt<bool>
namespace llvm {
namespace bolt {
+static bool isPossibleVeneer(const BinaryFunction &BF) {
+ return BF.isAArch64Veneer() || BF.getOneName().starts_with("__AArch64");
+}
+
Error VeneerElimination::runOnFunctions(BinaryContext &BC) {
if (!opts::EliminateVeneers || !BC.isAArch64())
return Error::success();
std::map<uint64_t, BinaryFunction> &BFs = BC.getBinaryFunctions();
std::unordered_map<const MCSymbol *, const MCSymbol *> VeneerDestinations;
- uint64_t VeneersCount = 0;
- for (auto &It : BFs) {
- BinaryFunction &VeneerFunction = It.second;
- if (!VeneerFunction.isAArch64Veneer())
+ uint64_t NumEliminatedVeneers = 0;
+ for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
+ if (!isPossibleVeneer(BF))
+ continue;
+
+ if (BF.isIgnored())
continue;
- VeneersCount++;
- VeneerFunction.setPseudo(true);
- MCInst &FirstInstruction = *(VeneerFunction.begin()->begin());
- const MCSymbol *VeneerTargetSymbol =
- BC.MIB->getTargetSymbol(FirstInstruction, 1);
- assert(VeneerTargetSymbol && "Expecting target symbol for instruction");
- for (const MCSymbol *Symbol : VeneerFunction.getSymbols())
+ MCInst &FirstInstruction = *(BF.begin()->begin());
+ const MCSymbol *VeneerTargetSymbol = 0;
+ uint64_t TargetAddress;
+ if (BC.MIB->matchAbsLongVeneer(BF, TargetAddress)) {
+ if (BinaryFunction *TargetBF =
+ BC.getBinaryFunctionAtAddress(TargetAddress))
+ VeneerTargetSymbol = TargetBF->getSymbol();
+ } else {
+ if (!BC.MIB->hasAnnotation(FirstInstruction, "AArch64Veneer"))
+ continue;
+ VeneerTargetSymbol = BC.MIB->getTargetSymbol(FirstInstruction, 1);
+ }
+
+ if (!VeneerTargetSymbol)
+ continue;
+
+ for (const MCSymbol *Symbol : BF.getSymbols())
VeneerDestinations[Symbol] = VeneerTargetSymbol;
+
+ NumEliminatedVeneers++;
+ BF.setPseudo(true);
}
BC.outs() << "BOLT-INFO: number of removed linker-inserted veneers: "
- << VeneersCount << "\n";
+ << NumEliminatedVeneers << '\n';
// Handle veneers to veneers in case they occur
for (auto &Entry : VeneerDestinations) {
diff --git a/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp b/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
index f58f7857e28aeb..1012ff77d6f66a 100644
--- a/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
+++ b/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
@@ -15,6 +15,8 @@
#include "MCTargetDesc/AArch64MCExpr.h"
#include "MCTargetDesc/AArch64MCTargetDesc.h"
#include "Utils/AArch64BaseInfo.h"
+#include "bolt/Core/BinaryBasicBlock.h"
+#include "bolt/Core/BinaryFunction.h"
#include "bolt/Core/MCPlusBuilder.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/MC/MCContext.h"
@@ -22,6 +24,7 @@
#include "llvm/MC/MCInstBuilder.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/Support/DataExtractor.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
@@ -1320,6 +1323,67 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
return 3;
}
+ /// Match the following pattern:
+ ///
+ /// ADR x16, .L1
+ /// BR x16
+ /// L1:
+ /// .quad Target
+ ///
+ /// Populate \p TargetAddress with the Target value on successful match.
+ bool matchAbsLongVeneer(const BinaryFunction &BF,
+ uint64_t &TargetAddress) const override {
+ if (BF.size() != 1 || BF.getMaxSize() < 16)
+ return false;
+
+ if (!BF.hasConstantIsland())
+ return false;
+
+ const BinaryBasicBlock &BB = BF.front();
+ if (BB.size() != 2)
+ return false;
+
+ const MCInst &LDRInst = BB.getInstructionAtIndex(0);
+ if (LDRInst.getOpcode() != AArch64::LDRXl)
+ return false;
+
+ if (!LDRInst.getOperand(0).isReg() ||
+ LDRInst.getOperand(0).getReg() != AArch64::X16)
+ return false;
+
+ const MCSymbol *TargetSym = getTargetSymbol(LDRInst, 1);
+ if (!TargetSym)
+ return false;
+
+ const MCInst &BRInst = BB.getInstructionAtIndex(1);
+ if (BRInst.getOpcode() != AArch64::BR)
+ return false;
+ if (!BRInst.getOperand(0).isReg() ||
+ BRInst.getOperand(0).getReg() != AArch64::X16)
+ return false;
+
+ const BinaryFunction::IslandInfo &IInfo = BF.getIslandInfo();
+ if (IInfo.HasDynamicRelocations)
+ return false;
+
+ auto Iter = IInfo.Offsets.find(8);
+ if (Iter == IInfo.Offsets.end() || Iter->second != TargetSym)
+ return false;
+
+ // Extract the absolute value stored inside the island.
+ StringRef SectionContents = BF.getOriginSection()->getContents();
+ StringRef FunctionContents = SectionContents.substr(
+ BF.getAddress() - BF.getOriginSection()->getAddress(), BF.getMaxSize());
+
+ const BinaryContext &BC = BF.getBinaryContext();
+ DataExtractor DE(FunctionContents, BC.AsmInfo->isLittleEndian(),
+ BC.AsmInfo->getCodePointerSize());
+ uint64_t Offset = 8;
+ TargetAddress = DE.getAddress(&Offset);
+
+ return true;
+ }
+
bool matchAdrpAddPair(const MCInst &Adrp, const MCInst &Add) const override {
if (!isADRP(Adrp) || !isAddXri(Add))
return false;
diff --git a/bolt/test/AArch64/veneer-lld-abs.s b/bolt/test/AArch64/veneer-lld-abs.s
new file mode 100644
index 00000000000000..d10ff46e2cb016
--- /dev/null
+++ b/bolt/test/AArch64/veneer-lld-abs.s
@@ -0,0 +1,51 @@
+## Check that llvm-bolt correctly recognizes long absolute thunks generated
+## by LLD.
+
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %s -o %t.o
+# RUN: %clang %cflags -fno-PIC -no-pie %t.o -o %t.exe -nostdlib \
+# RUN: -fuse-ld=lld -Wl,-q
+# RUN: llvm-objdump -d %t.exe | FileCheck --check-prefix=CHECK-INPUT %s
+# RUN: llvm-objcopy --remove-section .rela.mytext %t.exe
+# RUN: llvm-bolt %t.exe -o %t.bolt --elim-link-veneers=true --lite=0
+# RUN: llvm-objdump -d -j .text %t.bolt | \
+# RUN: FileCheck --check-prefix=CHECK-OUTPUT %s
+
+.text
+.balign 4
+.global foo
+.type foo, %function
+foo:
+ adrp x1, foo
+ ret
+.size foo, .-foo
+
+.section ".mytext", "ax"
+.balign 4
+
+.global __AArch64AbsLongThunk_foo
+.type __AArch64AbsLongThunk_foo, %function
+__AArch64AbsLongThunk_foo:
+ ldr x16, .L1
+ br x16
+# CHECK-INPUT-LABEL: <__AArch64AbsLongThunk_foo>:
+# CHECK-INPUT-NEXT: ldr
+# CHECK-INPUT-NEXT: br
+.L1:
+ .quad foo
+.size __AArch64AbsLongThunk_foo, .-__AArch64AbsLongThunk_foo
+
+## Check that the thunk was removed from .text and _start() calls foo()
+## directly.
+
+# CHECK-OUTPUT-NOT: __AArch64AbsLongThunk_foo
+
+.global _start
+.type _start, %function
+_start:
+# CHECK-INPUT-LABEL: <_start>:
+# CHECK-OUTPUT-LABEL: <_start>:
+ bl __AArch64AbsLongThunk_foo
+# CHECK-INPUT-NEXT: bl {{.*}} <__AArch64AbsLongThunk_foo>
+# CHECK-OUTPUT-NEXT: bl {{.*}} <foo>
+ ret
+.size _start, .-_start
``````````
</details>
https://github.com/llvm/llvm-project/pull/113408
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