[llvm-dev] Status of stack walking in LLVM on Win64?

[Hayden Livingston via llvm-dev]

For JITs it would appear that there is a patch needed for some kind of
relocations.

https://llvm.org/bugs/show_bug.cgi?id=24233

Is the patch really needed? What does it do? I'm not an expert here so asking.

On Sun, Jul 3, 2016 at 2:48 AM, David Majnemer via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
>
> On Sat, Jul 2, 2016 at 5:22 PM, Michael Lewis via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>>
>> Hi all,
>>
>> I'm developing a novel language that has historically used LLVM for code
>> generation, behind a custom self-hosted front-end. The runtime for this
>> language offers a garbage collector.
>>
>> In the past I've been on 32-bit Windows where precise garbage collection
>> is relatively straightforward (as long as FPO is disabled). Walking the
>> stack is a simple bit of pointer chasing and some fixups. I've had a working
>> GC on Win32 for years and actually posted here in the past about my
>> experience with .gcroot and other related miscellany involved in building a
>> real GC with LLVM.
>>
>>
>> Recently I've decided to begin moving the language to 64-bit native, and
>> this has posed a few interesting challenges. The most pressing issue for me
>> now is that stack walking is very different on Win64. It is not immediately
>> clear to me if LLVM (3.8 or ToT) is in a position to enable reliable stack
>> walks.
>>
>> Please note I'm using purely AoT compilation here with a custom
>> linker/binary image emitter. I can sort of hack things up in JITted code
>> using a manual process to populate data for RtlAddFunctionTable but I'm
>> ultimately not interested in JIT code generation.
>>
>>
>> I've managed to intercept data destined for the .pdata and .xdata COFF
>> sections, but it seems to be garbage. All functions claim to begin at offset
>> 0x0 and the UNWIND_INFO offsets are all 0-based instead of pointing into any
>> relevant part of the image.
>>
>>
>> Given a day or so I could provide a small example that generates this
>> useless data, but before I go to that extent - am I just doing something
>> dumb/forgetting a step/etc. when it comes to generating stack walk metadata
>> on Win64? Does LLVM even emit correct data yet when doing AoT compilation?
>
>
> I can confirm that LLVM emits correct data when used in an AoT configuration
> for x64, exception handling would be totally broken without it.
>
>>
>>
>>
>>
>> Thanks,
>>
>>
>>
>>  - Mike
>>
>>
>>
>>
>>
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>>
>
>
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