Commit f0b2f695 authored by Amy Kwan's avatar Amy Kwan
Browse files

[AIX][TLS] Generate .extern and .ref references to __tls_get_addr for local-exec accesses. 

Compiling with TLS variables requires -pthread, but if the user omits this
option, the compiler will not show any obvious indication during compilation
that -pthread is needed for programs using TLS variables. Instead, the user will
experience a segmentation fault when running programs with TLS variables in them
and without specifying -pthread.

This patch aims to generate .extern/.ref references to __tls_get_addr[DS] for
local-exec accesses, in order to trigger an error from the linker to indicate
that there is an undefined symbol to __tls_get_addr. Doing so will remind the
user to compile/link with -pthread.

Differential Revision: https://reviews.llvm.org/D151335
parent be0e42c1

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

+34 −5
Original line number Diff line number Diff line
@@ -171,6 +171,11 @@ public: 
    TOCType_EHBlock

  };



  // Controls whether or not to emit a .ref reference to __tls_get_addr.

  // This is currently used for TLS models that do not generate calls to

  // TLS functions, such as for the local-exec model on AIX 64-bit.

  bool HasRefGetTLSAddr = false;



  MCSymbol *lookUpOrCreateTOCEntry(const MCSymbol *Sym, TOCEntryType Type,

                                   MCSymbolRefExpr::VariantKind Kind =

                                       MCSymbolRefExpr::VariantKind::VK_None);
@@ -615,12 +620,17 @@ void PPCAsmPrinter::LowerPATCHPOINT(StackMaps &SM, const MachineInstr &MI) { 
/// This helper function creates the TlsGetAddr MCSymbol for AIX. We will

/// create the csect and use the qual-name symbol instead of creating just the

/// external symbol.

static MCSymbol *createMCSymbolForTlsGetAddr(MCContext &Ctx, unsigned MIOpc) {

  StringRef SymName =

      MIOpc == PPC::GETtlsTpointer32AIX ? ".__get_tpointer" : ".__tls_get_addr";

static MCSymbol *

createMCSymbolForTlsGetAddr(MCContext &Ctx, unsigned MIOpc,

                            XCOFF::StorageMappingClass SMC = XCOFF::XMC_PR) {

  StringRef SymName;

  if (MIOpc == PPC::GETtlsTpointer32AIX)

    SymName = ".__get_tpointer";

  else

    SymName = (SMC == XCOFF::XMC_DS) ? "__tls_get_addr" : ".__tls_get_addr";

  return Ctx

      .getXCOFFSection(SymName, SectionKind::getText(),

                       XCOFF::CsectProperties(XCOFF::XMC_PR, XCOFF::XTY_ER))

                       XCOFF::CsectProperties(SMC, XCOFF::XTY_ER))

      ->getQualNameSymbol();

}
@@ -832,8 +842,11 @@ void PPCAsmPrinter::emitInstruction(const MachineInstr *MI) { 
    if (MO.getTargetFlags() & PPCII::MO_TPREL_FLAG) {

      assert(MO.isGlobal() && "Only expecting a global MachineOperand here!\n");

      TLSModel::Model Model = TM.getTLSModel(MO.getGlobal());

      if (Model == TLSModel::LocalExec)

      if (Model == TLSModel::LocalExec) {

        if (IsPPC64)

          HasRefGetTLSAddr = true;

        return MCSymbolRefExpr::VariantKind::VK_PPC_AIX_TLSLE;

      }

      if (Model == TLSModel::InitialExec)

        return MCSymbolRefExpr::VariantKind::VK_PPC_AIX_TLSIE;

      llvm_unreachable("Only expecting local-exec or initial-exec accesses!");
@@ -2862,6 +2875,22 @@ bool PPCAIXAsmPrinter::doFinalization(Module &M) { 
    OutStreamer->doFinalizationAtSectionEnd(

        OutStreamer->getContext().getObjectFileInfo()->getTextSection());



  // Add a single .ref reference to __tls_get_addr[DS] for the local-exec TLS

  // model on AIX 64-bit. For TLS models that do not generate calls to TLS

  // functions, this reference to __tls_get_addr helps generate a linker error

  // to an undefined symbol to __tls_get_addr, which indicates to the user that

  // compiling with -pthread is required for programs that use TLS variables.

  if (HasRefGetTLSAddr) {

    // Specifically for 64-bit AIX, a load from the TOC is generated to load

    // the variable offset needed for local-exec accesses.

    MCSymbol *TlsGetAddrDescriptor =

        createMCSymbolForTlsGetAddr(OutContext, PPC::GETtlsADDR64AIX,

                                    XCOFF::XMC_DS);



    ExtSymSDNodeSymbols.insert(TlsGetAddrDescriptor);

    OutStreamer->emitXCOFFRefDirective(TlsGetAddrDescriptor);

  }



  for (MCSymbol *Sym : ExtSymSDNodeSymbols)

    OutStreamer->emitSymbolAttribute(Sym, MCSA_Extern);

  return PPCAsmPrinter::doFinalization(M);

llvm/test/CodeGen/PowerPC/aix-tls-le-ldst-double.ll

+7 −0
Original line number Diff line number Diff line
@@ -635,6 +635,13 @@ entry: 
  ret double %add

}



; (64-bit only) External symbol reference checks for __tls_get_addr[DS]



; SMALL64: .ref __tls_get_addr[DS]

; SMALL64: .extern __tls_get_addr[DS]

; LARGE64: .ref __tls_get_addr[DS]

; LARGE64: .extern __tls_get_addr[DS]



; TOC Entry Checks.



; SMALL64-LABEL: .toc

llvm/test/CodeGen/PowerPC/aix-tls-le-ldst-float.ll

+7 −0
Original line number Diff line number Diff line
@@ -635,6 +635,13 @@ entry: 
  ret float %add

}



; (64-bit only) External symbol reference checks for __tls_get_addr[DS]



; SMALL64: .ref __tls_get_addr[DS]

; SMALL64: .extern __tls_get_addr[DS]

; LARGE64: .ref __tls_get_addr[DS]

; LARGE64: .extern __tls_get_addr[DS]



; TOC Entry Checks.



; SMALL64-LABEL: .toc

llvm/test/CodeGen/PowerPC/aix-tls-le-ldst-int.ll

+7 −0
Original line number Diff line number Diff line
@@ -651,6 +651,13 @@ entry: 
  ret i32 %add

}



; (64-bit only) External symbol reference checks for __tls_get_addr[DS]



; SMALL64: .ref __tls_get_addr[DS]

; SMALL64: .extern __tls_get_addr[DS]

; LARGE64: .ref __tls_get_addr[DS]

; LARGE64: .extern __tls_get_addr[DS]



; TOC Entry Checks.



; SMALL64-LABEL: .toc

llvm/test/CodeGen/PowerPC/aix-tls-le-ldst-longlong.ll

+7 −0
Original line number Diff line number Diff line
@@ -707,6 +707,13 @@ entry: 
  ret i64 %add

}



; (64-bit only) External symbol reference checks for __tls_get_addr[DS]



; SMALL64: .ref __tls_get_addr[DS]

; SMALL64: .extern __tls_get_addr[DS]

; LARGE64: .ref __tls_get_addr[DS]

; LARGE64: .extern __tls_get_addr[DS]



; TOC Entry Checks.



; SMALL64-LABEL: .toc