[llvm] r192118 - Formally added an explicit enum for DWARF TLS support. No functionality change.

[Adrian Prantl]

Hi Richard,

[Apologies for replying to age-old commits]
I’m wondering why we are using the custom DW_OP_GNU_push_tls_address when there is a DW_OP_form_tls_address since DWARF 3. Are there historical or technical reasons why we do this? Could we change it to use the DWARF version?

-- adrian

On Oct 7, 2013, at 11:39, Richard Mitton <richard at codersnotes.com> wrote:

> Author: rmitton
> Date: Mon Oct  7 13:39:18 2013
> New Revision: 192118
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=192118&view=rev
> Log:
> Formally added an explicit enum for DWARF TLS support. No functionality change.
> 
> Modified:
>    llvm/trunk/include/llvm/Support/Dwarf.h
>    llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
>    llvm/trunk/lib/Support/Dwarf.cpp
> 
> Modified: llvm/trunk/include/llvm/Support/Dwarf.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/Dwarf.h?rev=192118&r1=192117&r2=192118&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/Support/Dwarf.h (original)
> +++ llvm/trunk/include/llvm/Support/Dwarf.h Mon Oct  7 13:39:18 2013
> @@ -486,6 +486,9 @@ enum Constants {
>   DW_OP_lo_user = 0xe0,
>   DW_OP_hi_user = 0xff,
> 
> +  // Extensions for GNU-style thread-local storage.
> +  DW_OP_GNU_push_tls_address = 0xe0,
> +
>   // Extensions for Fission proposal.
>   DW_OP_GNU_addr_index = 0xfb,
>   DW_OP_GNU_const_index = 0xfc,
> 
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp?rev=192118&r1=192117&r2=192118&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp Mon Oct  7 13:39:18 2013
> @@ -1505,14 +1505,15 @@ void CompileUnit::createGlobalVariableDI
>         // 1) Start with a constNu of the appropriate pointer size
>         addUInt(Block, 0, dwarf::DW_FORM_data1,
>                 PointerSize == 4 ? dwarf::DW_OP_const4u : dwarf::DW_OP_const8u);
> -        // 2) containing the (relocated) address of the TLS variable
> +        // 2) containing the (relocated) offset of the TLS variable
> +        //    within the module's TLS block.
>         addExpr(Block, 0, dwarf::DW_FORM_udata, Expr);
>       } else {
>         addUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_GNU_const_index);
>         addUInt(Block, 0, dwarf::DW_FORM_udata, DU->getAddrPoolIndex(Expr));
>       }
> -      // 3) followed by a custom OP to tell the debugger about TLS (presumably)
> -      addUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_lo_user);
> +      // 3) followed by a custom OP to make the debugger do a TLS lookup.
> +      addUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_GNU_push_tls_address);
>     } else
>       addOpAddress(Block, Sym);
>     // Do not create specification DIE if context is either compile unit
> 
> Modified: llvm/trunk/lib/Support/Dwarf.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Dwarf.cpp?rev=192118&r1=192117&r2=192118&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Support/Dwarf.cpp (original)
> +++ llvm/trunk/lib/Support/Dwarf.cpp Mon Oct  7 13:39:18 2013
> @@ -456,10 +456,11 @@ const char *llvm::dwarf::OperationEncodi
>   case DW_OP_bit_piece:                  return "DW_OP_bit_piece";
>   case DW_OP_implicit_value:             return "DW_OP_implicit_value";
>   case DW_OP_stack_value:                return "DW_OP_stack_value";
> -  case DW_OP_lo_user:                    return "DW_OP_lo_user";
> -  case DW_OP_hi_user:                    return "DW_OP_hi_user";
> 
> -    // DWARF5 Fission Proposal Op Extensions
> +  // GNU thread-local storage
> +  case DW_OP_GNU_push_tls_address:       return "DW_OP_GNU_push_tls_address";
> +
> +  // DWARF5 Fission Proposal Op Extensions
>   case DW_OP_GNU_addr_index:             return "DW_OP_GNU_addr_index";
>   case DW_OP_GNU_const_index:            return "DW_OP_GNU_const_index";
>   }
> 
> 
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