[cfe-dev] debug_frame section not generated for Windows 64bit

[Reid Kleckner via cfe-dev]

Got it. I think the CFA is always the address of the return address, so
such a DWARF consumer could be retrofitted to parse .xdata, find the
caller's return address, and evaluate expressions using the CFA from there.

I don't think it's possible to get LLVM to emit DWARF CFI and Win CFI at
the same time. The booleans in the prologue emission suggest that they are
mutually exlusive:
  bool IsWin64Prologue = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
  ...
  bool NeedsDwarfCFI =
      !IsWin64Prologue && (MMI.hasDebugInfo() ||
Fn.needsUnwindTableEntry());

NeedsDwarfCFI controls the emission of the DWARF .cfi_* directives, which
normally produce the .eh_frame or .debug_frame sections.

Shoaib, I think you have users of DWARF on Windows? How do they deal with
this problem?


On Fri, Mar 23, 2018 at 12:06 AM Jayvee Neumann via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi Reid,
>
> your suggestion is not a solution to the problem I have. I still want to
> use SEH on 64bit Windows because it is, as you also pointed out, required
> by the ABI. I need a .debug_frame or .eh_frame section in addition to the
> SEH .pdata section. I am aware that the exception handling data would be
> redundant. Information about e.g. the CFA, which is required by some
> DWARF-expressions/locations, would not be redundant though.
>
> Is there a way to request both, a .pdata section for SEH style exceptions
> and a .debug_frame sections, in the same or a similar way to MinGW-w64?
>
> Best Regards
> Jayvee
>
> 2018-03-23 0:22 GMT+01:00 Reid Kleckner <rnk at google.com>:
>
>> Clang defaults to emitting SEH unwind information on Win64, since it is
>> required by the ABI. DWARF EH tables would be redundant, but you can
>> request them with -fdwarf-exceptions.
>>
>>
>> On Thu, Mar 22, 2018 at 4:05 PM Jayvee Neumann via cfe-dev <
>> cfe-dev at lists.llvm.org> wrote:
>>
>>> Hi togehter,
>>>
>>> I am currently switching from MinGW-w64 to clang. I am running into a
>>> problem with the debug information generated by clang, though. When
>>> building with mingw, there will always be an .eh_frame or a .debug_frame
>>> section. This is also true for 64bit windows. When I build the same files
>>> with clang for the target triple "x86_64-pc-windows-gnu" neither a
>>> .debug_frame nor an .eh_frame section is generated.
>>>
>>> I there a way for me to explicitly specify via command line that such a
>>> section shall be generated?
>>> If not, is there a way to change the llvm/clang source code in a way
>>> such that these sections will be generated for the specified target?
>>>
>>> Best Regards,
>>> Jayvee
>>> _______________________________________________
>>> cfe-dev mailing list
>>> cfe-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>
>>
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