From 07ee8d2fc1de1cd2fb66413fd14d328329334e88 Mon Sep 17 00:00:00 2001 From: Peter Collingbourne Date: Mon, 30 Mar 2015 20:41:21 +0000 Subject: [PATCH] MC: For variable symbols, maintain MCSymbol::Section as a cache. This fixes the visibility of symbols in certain edge cases involving aliases with multiple levels of indirection. Fixes PR19582. Differential Revision: http://reviews.llvm.org/D8586 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233595 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/llvm/MC/MCMachObjectWriter.h | 2 -- include/llvm/MC/MCSymbol.h | 26 +++++++++++++++++--------- lib/MC/MCExpr.cpp | 3 +++ lib/MC/MCSymbol.cpp | 8 +------- lib/MC/MachObjectWriter.cpp | 21 --------------------- lib/Target/X86/X86AsmPrinter.cpp | 1 - test/MC/ELF/alias-resolve.s | 8 ++++++++ test/MC/ELF/alias.s | 9 +++++++++ test/MC/MachO/ARM/aliased-symbols.s | 10 +++++----- 9 files changed, 43 insertions(+), 45 deletions(-) create mode 100644 test/MC/ELF/alias-resolve.s diff --git a/include/llvm/MC/MCMachObjectWriter.h b/include/llvm/MC/MCMachObjectWriter.h index 514700bce35..3d270ce7e0d 100644 --- a/include/llvm/MC/MCMachObjectWriter.h +++ b/include/llvm/MC/MCMachObjectWriter.h @@ -257,8 +257,6 @@ public: void computeSectionAddresses(const MCAssembler &Asm, const MCAsmLayout &Layout); - void markAbsoluteVariableSymbols(MCAssembler &Asm, - const MCAsmLayout &Layout); void ExecutePostLayoutBinding(MCAssembler &Asm, const MCAsmLayout &Layout) override; diff --git a/include/llvm/MC/MCSymbol.h b/include/llvm/MC/MCSymbol.h index 53443b01d96..e4bdfda55d6 100644 --- a/include/llvm/MC/MCSymbol.h +++ b/include/llvm/MC/MCSymbol.h @@ -15,6 +15,7 @@ #define LLVM_MC_MCSYMBOL_H #include "llvm/ADT/StringRef.h" +#include "llvm/MC/MCExpr.h" #include "llvm/Support/Compiler.h" namespace llvm { @@ -42,8 +43,9 @@ namespace llvm { /// Section - The section the symbol is defined in. This is null for /// undefined symbols, and the special AbsolutePseudoSection value for - /// absolute symbols. - const MCSection *Section; + /// absolute symbols. If this is a variable symbol, this caches the + /// variable value's section. + mutable const MCSection *Section; /// Value - If non-null, the value for a variable symbol. const MCExpr *Value; @@ -68,6 +70,12 @@ namespace llvm { MCSymbol(const MCSymbol&) = delete; void operator=(const MCSymbol&) = delete; + const MCSection *getSectionPtr() const { + if (Section || !Value) + return Section; + return Section = Value->FindAssociatedSection(); + } + public: /// getName - Get the symbol name. StringRef getName() const { return Name; } @@ -103,7 +111,7 @@ namespace llvm { /// /// Defined symbols are either absolute or in some section. bool isDefined() const { - return Section != nullptr; + return getSectionPtr() != nullptr; } /// isInSection - Check if this symbol is defined in some section (i.e., it @@ -119,27 +127,27 @@ namespace llvm { /// isAbsolute - Check if this is an absolute symbol. bool isAbsolute() const { - return Section == AbsolutePseudoSection; + return getSectionPtr() == AbsolutePseudoSection; } /// getSection - Get the section associated with a defined, non-absolute /// symbol. const MCSection &getSection() const { assert(isInSection() && "Invalid accessor!"); - return *Section; + return *getSectionPtr(); } /// setSection - Mark the symbol as defined in the section \p S. - void setSection(const MCSection &S) { Section = &S; } + void setSection(const MCSection &S) { + assert(!isVariable() && "Cannot set section of variable"); + Section = &S; + } /// setUndefined - Mark the symbol as undefined. void setUndefined() { Section = nullptr; } - /// setAbsolute - Mark the symbol as absolute. - void setAbsolute() { Section = AbsolutePseudoSection; } - /// @} /// @name Variable Symbols /// @{ diff --git a/lib/MC/MCExpr.cpp b/lib/MC/MCExpr.cpp index 8a64403362c..995f4c96ee6 100644 --- a/lib/MC/MCExpr.cpp +++ b/lib/MC/MCExpr.cpp @@ -775,6 +775,9 @@ const MCSection *MCExpr::FindAssociatedSection() const { if (RHS_S == MCSymbol::AbsolutePseudoSection) return LHS_S; + if (BE->getOpcode() == MCBinaryExpr::Sub) + return MCSymbol::AbsolutePseudoSection; + // Otherwise, return the first non-null section. return LHS_S ? LHS_S : RHS_S; } diff --git a/lib/MC/MCSymbol.cpp b/lib/MC/MCSymbol.cpp index 24165254e56..6582574ae94 100644 --- a/lib/MC/MCSymbol.cpp +++ b/lib/MC/MCSymbol.cpp @@ -55,13 +55,7 @@ void MCSymbol::setVariableValue(const MCExpr *Value) { assert(!IsUsed && "Cannot set a variable that has already been used."); assert(Value && "Invalid variable value!"); this->Value = Value; - - // Variables should always be marked as in the same "section" as the value. - const MCSection *Section = Value->FindAssociatedSection(); - if (Section) - setSection(*Section); - else - setUndefined(); + this->Section = nullptr; } void MCSymbol::print(raw_ostream &OS) const { diff --git a/lib/MC/MachObjectWriter.cpp b/lib/MC/MachObjectWriter.cpp index 5e9e86f18a0..56cccab1d39 100644 --- a/lib/MC/MachObjectWriter.cpp +++ b/lib/MC/MachObjectWriter.cpp @@ -649,33 +649,12 @@ void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm, } } -void MachObjectWriter::markAbsoluteVariableSymbols(MCAssembler &Asm, - const MCAsmLayout &Layout) { - for (MCSymbolData &SD : Asm.symbols()) { - if (!SD.getSymbol().isVariable()) - continue; - - // Is the variable is a symbol difference (SA - SB + C) expression, - // and neither symbol is external, mark the variable as absolute. - const MCExpr *Expr = SD.getSymbol().getVariableValue(); - MCValue Value; - if (Expr->EvaluateAsRelocatable(Value, &Layout, nullptr)) { - if (Value.getSymA() && Value.getSymB()) - const_cast(&SD.getSymbol())->setAbsolute(); - } - } -} - void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, const MCAsmLayout &Layout) { computeSectionAddresses(Asm, Layout); // Create symbol data for any indirect symbols. BindIndirectSymbols(Asm); - - // Mark symbol difference expressions in variables (from .set or = directives) - // as absolute. - markAbsoluteVariableSymbols(Asm, Layout); } bool MachObjectWriter:: diff --git a/lib/Target/X86/X86AsmPrinter.cpp b/lib/Target/X86/X86AsmPrinter.cpp index f6033a7e157..a84f0585aea 100644 --- a/lib/Target/X86/X86AsmPrinter.cpp +++ b/lib/Target/X86/X86AsmPrinter.cpp @@ -523,7 +523,6 @@ void X86AsmPrinter::EmitStartOfAsmFile(Module &M) { // must be registered in .sxdata. Use of any unregistered handlers will // cause the process to terminate immediately. LLVM does not know how to // register any SEH handlers, so its object files should be safe. - S->setAbsolute(); OutStreamer.EmitSymbolAttribute(S, MCSA_Global); OutStreamer.EmitAssignment( S, MCConstantExpr::Create(int64_t(1), MMI->getContext())); diff --git a/test/MC/ELF/alias-resolve.s b/test/MC/ELF/alias-resolve.s new file mode 100644 index 00000000000..304cacb2972 --- /dev/null +++ b/test/MC/ELF/alias-resolve.s @@ -0,0 +1,8 @@ +// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -r | FileCheck %s + +a: + .section foo + c = b +b: + // CHECK: 0x0 R_X86_64_PC32 .text 0x0 + .long a - c diff --git a/test/MC/ELF/alias.s b/test/MC/ELF/alias.s index 78df7371d25..0ab6dd4b5b8 100644 --- a/test/MC/ELF/alias.s +++ b/test/MC/ELF/alias.s @@ -24,6 +24,15 @@ bar5 = bar4 bar6 = bar5 bar6: +// Test that indirect local aliases do not appear as symbols. +.data +.Llocal: + +.text +leaq .Llocal1(%rip), %rdi +.Llocal1 = .Llocal2 +.Llocal2 = .Llocal + // CHECK: Symbols [ // CHECK-NEXT: Symbol { // CHECK-NEXT: Name: (0) diff --git a/test/MC/MachO/ARM/aliased-symbols.s b/test/MC/MachO/ARM/aliased-symbols.s index e87b81c6a15..cc2e200ce8a 100644 --- a/test/MC/MachO/ARM/aliased-symbols.s +++ b/test/MC/MachO/ARM/aliased-symbols.s @@ -45,9 +45,9 @@ Ltmp0: // CHECK-NEXT: Value: 0x[[DEFINED_EARLY]] // CHECK-NEXT: } - // defined_late was defined. Just after defined_early. + // alias_to_late was an alias to defined_late. But we can resolve it. // CHECK: Symbol { -// CHECK-NEXT: Name: defined_late +// CHECK-NEXT: Name: alias_to_late // CHECK-NEXT: Type: Section (0xE) // CHECK-NEXT: Section: __data (0x2) // CHECK-NEXT: RefType: UndefinedNonLazy (0x0) @@ -56,9 +56,9 @@ Ltmp0: // CHECK-NEXT: Value: 0x[[DEFINED_LATE:[0-9A-F]+]] // CHECK-NEXT: } - // alias_to_late was an alias to defined_late. But we can resolve it. + // defined_late was defined. Just after defined_early. // CHECK: Symbol { -// CHECK-NEXT: Name: alias_to_late +// CHECK-NEXT: Name: defined_late // CHECK-NEXT: Type: Section (0xE) // CHECK-NEXT: Section: __data (0x2) // CHECK-NEXT: RefType: UndefinedNonLazy (0x0) @@ -72,7 +72,7 @@ Ltmp0: // CHECK: Symbol { // CHECK-NEXT: Name: alias_to_local (42) // CHECK-NEXT: Type: Section (0xE) -// CHECK-NEXT: Section: (0x0) +// CHECK-NEXT: Section: __data (0x2) // CHECK-NEXT: RefType: UndefinedNonLazy (0x0) // CHECK-NEXT: Flags [ (0x0) // CHECK-NEXT: ]