From 0be69b14dca34f72429c96615197cd512ad867ff Mon Sep 17 00:00:00 2001 From: Reid Kleckner Date: Thu, 29 Dec 2016 00:12:39 +0000 Subject: [PATCH] [COFF] Use 32-bit jump table entries in .rdata for Win64 Summary: We were already using 32-bit jump table entries, but this was a consequence of the default PIC model on Win64, and not an intentional design decision. This patch ensures that we always use 32-bit label difference jump table entries on Win64 regardless of the PIC model. This is a good idea because it saves executable size and object file size. Moving the jump tables to .rdata cleans up the disassembled object code and reduces the available ROP targets, but it requires adding one more RIP-relative lea to the code. COFF doesn't have relocations to express the difference between two arbitrary symbols, so we can't use the jump table label in the label difference like we do elsewhere. Fixes PR31488 Reviewers: majnemer, compnerd Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D28141 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290694 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../CodeGen/TargetLoweringObjectFileImpl.h | 3 +++ lib/CodeGen/TargetLoweringObjectFileImpl.cpp | 7 +++++ lib/Target/X86/X86ISelLowering.cpp | 25 ++++++++++++++++++ lib/Target/X86/X86ISelLowering.h | 1 + test/CodeGen/X86/win64-jumptable.ll | 26 ++++++++++++------- 5 files changed, 53 insertions(+), 9 deletions(-) diff --git a/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h b/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h index cc71fa3918a..1839b6275c5 100644 --- a/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h +++ b/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h @@ -156,6 +156,9 @@ public: MCSection *getSectionForJumpTable(const Function &F, const TargetMachine &TM) const override; + bool shouldPutJumpTableInFunctionSection(bool UsesLabelDifference, + const Function &F) const override; + /// Emit Obj-C garbage collection and linker options. Only linker option /// emission is implemented for COFF. void emitModuleFlags(MCStreamer &Streamer, diff --git a/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/lib/CodeGen/TargetLoweringObjectFileImpl.cpp index eb2a28f574a..d19ca47ec1a 100644 --- a/lib/CodeGen/TargetLoweringObjectFileImpl.cpp +++ b/lib/CodeGen/TargetLoweringObjectFileImpl.cpp @@ -1055,6 +1055,13 @@ MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable( COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE, UniqueID); } +bool TargetLoweringObjectFileCOFF::shouldPutJumpTableInFunctionSection( + bool UsesLabelDifference, const Function &F) const { + // We can always create relative relocations, so use another section + // that can be marked non-executable. + return false; +} + void TargetLoweringObjectFileCOFF::emitModuleFlags( MCStreamer &Streamer, ArrayRef ModuleFlags, const TargetMachine &TM) const { diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp index b293dfa98f8..d0c77030acd 100644 --- a/lib/Target/X86/X86ISelLowering.cpp +++ b/lib/Target/X86/X86ISelLowering.cpp @@ -1926,10 +1926,20 @@ unsigned X86TargetLowering::getJumpTableEncoding() const { if (isPositionIndependent() && Subtarget.isPICStyleGOT()) return MachineJumpTableInfo::EK_Custom32; + // On Win64, we want to use both label differences and a separate section. + if (Subtarget.isTargetWin64()) + return MachineJumpTableInfo::EK_LabelDifference32; + // Otherwise, use the normal jump table encoding heuristics. return TargetLowering::getJumpTableEncoding(); } +bool X86TargetLowering::isJumpTableRelative() const { + if (Subtarget.isTargetWin64()) + return true; + return TargetLowering::isJumpTableRelative(); +} + bool X86TargetLowering::useSoftFloat() const { return Subtarget.useSoftFloat(); } @@ -1948,11 +1958,19 @@ X86TargetLowering::LowerCustomJumpTableEntry(const MachineJumpTableInfo *MJTI, /// Returns relocation base for the given PIC jumptable. SDValue X86TargetLowering::getPICJumpTableRelocBase(SDValue Table, SelectionDAG &DAG) const { + // COFF doesn't have relocations to take the difference between two arbitrary + // symbols. The assembler, however, can resolve a fixup between the function + // entry and a basic block label, so use the function entry as the base. + if (Subtarget.isTargetWin64()) + return DAG.getGlobalAddress(DAG.getMachineFunction().getFunction(), SDLoc(), + getPointerTy(DAG.getDataLayout())); + if (!Subtarget.is64Bit()) // This doesn't have SDLoc associated with it, but is not really the // same as a Register. return DAG.getNode(X86ISD::GlobalBaseReg, SDLoc(), getPointerTy(DAG.getDataLayout())); + return Table; } @@ -1961,6 +1979,13 @@ SDValue X86TargetLowering::getPICJumpTableRelocBase(SDValue Table, const MCExpr *X86TargetLowering:: getPICJumpTableRelocBaseExpr(const MachineFunction *MF, unsigned JTI, MCContext &Ctx) const { + // COFF doesn't have relocations to take the difference between two arbitrary + // symbols. The assembler, however, can resolve a fixup between the function + // entry and a basic block label, so use the function entry as the base. + if (Subtarget.isTargetWin64()) + return MCSymbolRefExpr::create( + getTargetMachine().getSymbol(MF->getFunction()), Ctx); + // X86-64 uses RIP relative addressing based on the jump table label. if (Subtarget.isPICStyleRIPRel()) return TargetLowering::getPICJumpTableRelocBaseExpr(MF, JTI, Ctx); diff --git a/lib/Target/X86/X86ISelLowering.h b/lib/Target/X86/X86ISelLowering.h index 37f9353042b..643727d7aed 100644 --- a/lib/Target/X86/X86ISelLowering.h +++ b/lib/Target/X86/X86ISelLowering.h @@ -684,6 +684,7 @@ namespace llvm { const X86Subtarget &STI); unsigned getJumpTableEncoding() const override; + bool isJumpTableRelative() const override; bool useSoftFloat() const override; MVT getScalarShiftAmountTy(const DataLayout &, EVT) const override { diff --git a/test/CodeGen/X86/win64-jumptable.ll b/test/CodeGen/X86/win64-jumptable.ll index 6bb9d64c05c..4fd24918864 100644 --- a/test/CodeGen/X86/win64-jumptable.ll +++ b/test/CodeGen/X86/win64-jumptable.ll @@ -1,7 +1,5 @@ -; RUN: llc < %s -relocation-model static | FileCheck %s - -; FIXME: Remove '-relocation-model static' when it is no longer necessary to -; trigger the separate .rdata section. +; RUN: llc < %s -relocation-model static | FileCheck %s --check-prefix=CHECK --check-prefix=STATIC +; RUN: llc < %s -relocation-model pic | FileCheck %s --check-prefix=CHECK --check-prefix=PIC target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128" target triple = "x86_64-pc-windows-msvc19.0.24215" @@ -41,7 +39,17 @@ declare void @g(i32) ; CHECK: .text ; CHECK: f: ; CHECK: .seh_proc f -; CHECK: jmpq *.LJTI0_0 + +; STATIC: movslq .LJTI0_0(,%{{.*}},4), %[[target:[^ ]*]] +; STATIC: leaq f(%[[target]]), %[[target]] +; STATIC: jmpq *%[[target]] + +; PIC: leaq .LJTI0_0(%rip), %[[jt:[^ ]*]] +; PIC: movslq (%[[jt]],%{{.*}},4), %[[offset:[^ ]*]] +; PIC: leaq f(%rip), %[[base:[^ ]*]] +; PIC: addq %[[offset]], %[[base]] +; PIC: jmpq *%[[base]] + ; CHECK: .LBB0_{{.*}}: # %sw.bb ; CHECK: .LBB0_{{.*}}: # %sw.bb1 ; CHECK: .LBB0_{{.*}}: # %sw.bb2 @@ -49,10 +57,10 @@ declare void @g(i32) ; CHECK: callq g ; CHECK: jmp g # TAILCALL ; CHECK: .section .rdata,"dr" -; CHECK: .quad .LBB0_ -; CHECK: .quad .LBB0_ -; CHECK: .quad .LBB0_ -; CHECK: .quad .LBB0_ +; CHECK: .long .LBB0_{{.*}}-f +; CHECK: .long .LBB0_{{.*}}-f +; CHECK: .long .LBB0_{{.*}}-f +; CHECK: .long .LBB0_{{.*}}-f ; CHECK: .seh_handlerdata ; It's important that we switch back to .text here, not .rdata.