[llvm-dev] [MCJIT] messy call stack debug on x64 code in VisualStudio

[Jameson Nash via llvm-dev]

I've always just hacked support for this in to the various JITs (for
JuliaLang, in our debuginfo.cpp file), by setting the
no-frame-pointer-optim flag in the IR, then creating and populating a dummy
unwind description object in the .text section, and registering that
dynamically. Some day I hope to actually just register the .pdata/.xdata
sections with the unwinder.

PDBs are a bit different though, since the above steps work well for gdb,
but generally I find that WinDbg is less willing or able to be given
JIT-frame information from LLVM. (I assume somehow it can be done, for
dotNET. I just don't know how.)

On Sat, Feb 29, 2020 at 11:07 PM Reid Kleckner via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Yes, I think https://bugs.llvm.org/show_bug.cgi?id=24233 needs to be
> implemented to fix this.
>
> The Windows x64 unwinder doesn't generally look at frame pointers. We
> would need to register unwind info to make this work. What you see is
> fairly typical of attempting to unwind the stack when unwind info is
> missing.
>
> PDBs shouldn't generally enter into the picture.
>
> On Sat, Feb 29, 2020 at 8:14 AM Vivien Millet via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi,
>>
>> I'm using IR and MCJIT to compile a script language. I debug it with on
>> the fly generated .pdb files. During debugging, almost each time I step
>> into a function, I loose information about calling function inside the
>> visual studio callstack view or I have a bunch of pure addresses in the
>> callstack in between the current function and the calling function, for
>> example :
>>
>> MyJit.dll!MyCurrentFunction()
>> [0x1234567887654321]
>> [0x8765432112345678]
>> MyJit.dll!MyCallingFunction()
>> ...
>>
>> It looks like visual studio get lost while walking up stack.
>> Does anyone know where it could come from ?
>>
>> I have disabled all optimisations (among them is the omit-frame-pointer).
>>
>> I have seen this bug here : https://bugs.llvm.org/show_bug.cgi?id=24233 which
>> is quite similar but it is quite old now, and since the proposed patch has
>> been posted, the code in RuntimeDyldCOFFX86_64.h has changed and it is
>> difficult for me to know if it has really been fixed since or not.
>>
>> Could it be related to the way IR CreateAlloca are used to build local
>> variables ? Could it be related to missing informations inside the PDB ? (I
>> don't know if there is stack related information inside PDB files to ensure
>> good stack walking).
>>
>> Thanks.
>>
>> Vivien
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