[PATCH] D28265: disable sigaltstack on Apple platforms

[Davide Italiano via Phabricator via llvm-commits]

davide accepted this revision.
davide added a comment.
This revision is now accepted and ready to land.

In https://reviews.llvm.org/D28265#635541, @bob.wilson wrote:

> Yes, of course you are right that this is not ideal. It's not about avoiding crashes though -- the issue is that the backtraces we dump out after an assertion failure are useless since they stop at the signal handler.
>
> Your comment prompted me to look a little deeper, and I discovered that the _Unwind_Backtrace issue is not specific to sigaltstack. We first try to use the backtrace() function, and if you're not using sigaltstack, that succeeds and we never try using _Unwind_Backtrace. If I modify the code to skip trying backtrace(), I consistently get stack traces that stop at the signal handler after an assertion failure. I filed a bug report about that for libunwind (rdar://problem/29866587). As I mentioned earlier with r286851, I also filed a bug report about backtrace() not working with sigaltstack, but I didn't get the impression that was being treated as a high priority.
>
> Even if we get a fix for libunwind or backtrace (and I don't know if/when that might happen), it will take a while to get it released in macOS and we should wait a year or so beyond that so that the majority of LLVM developers will have updated to get the fix. In the meantime, we need this as a workaround. I should also revert my change in r286851 until _Unwind_Backtrace works reliably on Darwin.


Yes ... that's ... unfortunate. LGTM (with the hope that newer Mac OS/Darwin versions will ship with the fix)


https://reviews.llvm.org/D28265