[llvm-dev] Supporting libunwind on Windows 10 (32bit; 64bit) for MSVC and Clang

[Ivan Serdyuk via llvm-dev]

On Sat, Aug 15, 2020 at 8:39 PM Martin Storsjö <martin at martin.st> wrote:

> Hi,
>
>
> On Sat, 15 Aug 2020, Ivan Serdyuk wrote:
>
> >       Just as Shoaib said, libunwind only is useful in environments
> >       that use
> >       the Itanium C++ ABI - there's really no use for it in an MSVC
> >       context
> >       (either using MSVC or clang-cl to compile it).
> >
> >       The particular linker error comes from the fact that there's
> >       functions
> >       implemented in assembly, that expect the function name to be
> >       mangled the
> >       itanium way, while the object files built by the compiler expect
> >       the
> >       symbols to use the MSVC C++ name mangling, so there's an
> >       undefined
> >       reference.
> >
> >
> > I see, thanks.
> >
> > Which options exist for MSVC, in sense an alternative to libunwind and
> > libbacktrace ?
>
> Well for libunwind, there's really no use for it in an MSVC setting. All
> the unwinding functionality is already built into the operating system,
> available via the Rtl*Unwind* functions.
>

Martin,
you mean these functions
https://docs.microsoft.com/en-us/windows/win32/api/winnt/nf-winnt-rtlunwind
https://docs.microsoft.com/en-us/windows/win32/api/winnt/nf-winnt-rtlunwind2
https://docs.microsoft.com/en-us/windows/win32/api/winnt/nf-winnt-rtlunwindex
https://docs.microsoft.com/en-us/windows/win32/api/winnt/nf-winnt-rtlvirtualunwind
?

>
> For libbacktrace, I guess the _Unwind_Backtrace function in libunwind
> might work and be useful, even if the rest of libunwind doesn't make sense
> in such a context.


Ian,
please share your vision/propose some plan.


> I haven't tested this function on windows though, and
> it'd require you to fix the linker error one way or another.
>

I see.

>
> Another alternative, requiring much less code, would be to just extract
> the SEH version of _Unwind_Backtrace function from libgcc [1]. I think
> that function is fairly independent from the rest of libgcc and from the
> rest of the surrounding file, and only calls Windows system APIs.
>

Well, adding committers to the discussion.
Richard, Tristan, Bernd, Jon - please verify/elaborate.

Thanks in advance.
Ivan

>
> // Martin
>
> [1] https://github.com/gcc-mirror/gcc/blob/master/libgcc/unwind-seh.c#L434
>
>
>
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