[PATCH] D50564: Add support for SEH unwinding on Windows.

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo added a comment.

In https://reviews.llvm.org/D50564#1206370, @cdavis5x wrote:

> In https://reviews.llvm.org/D50564#1206302, @kristina wrote:
>
> > I'm all for this change except the core issue is that you're using libunwind as a shim around the actual unwinding API provided by Windows. It would be nice to have something that did not have to do that and was capable of performing unwinding of SEH-style exceptions without needing additional runtime support.
>
>
> It would be nice, but that would require extra work. We'd have to implement reading and interpreting unwind codes, and calling any handlers present at each frame (which all have a different calling convention from Itanium handlers), and handling chained unwind info... Or we could use the implementation that MS provided to us for free--and which gets loaded into every process anyway by virtue of being in NTDLL, and which is extremely well tested. Given all that, I'm wondering what implementing all that ourselves would gain us. I suppose we could eventually do all that, but for now, I think this is outside the scope of my change.


+1. I guess such a library would be very nice to have, but from the point of view of implementing exception handling, using the underlying APIs probably is the way to go. The other question, as posted before, is whether we want to wrap the whole CONTEXT structs in the UnwindCursor class and expose it via the unw_* set of APIs. It gives quite a significant amount of extra code here compared to libgcc's unwind-seh.c which is <500 loc altogether, providing only the _Unwind_* API, implementing it directly with the Windows Rtl* APIs from ntdll. That would give only a partial libunwind, with only the higher level API available, but that's the only part used for exception handling at least.


Repository:
  rUNW libunwind

https://reviews.llvm.org/D50564