On 31.10.17 10:28, Konstantin Belousov wrote:
On Mon, Oct 30, 2017 at 10:54:05PM +0100, Andreas Tobler wrote:
On 30.10.17 15:32, Tijl Coosemans wrote:
On Sun, 29 Oct 2017 20:40:46 +0100 Andreas Tobler <andreast-l...@fgznet.ch> 
Attached what I have for libgcc. It can be applied to gcc5-8, should
give no issues. The mentioned tc from this thread and mine,
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82635 do pass.

What do you think?

Like I said before the return address can be anything.  It could for
instance point to some instruction in a random function and then the
stack unwinder will think thread_start was called from that function.
There's no check you can add to libgcc to distinguish that from a
normal valid return address.

Maybe not, and most probably I do not understand what is happening. But
with my modification I survive the test case.

If no objections from your or Konstantin's side come up I will commit it
to the gcc repo. It will not 'fix' the issue, but it will improve the
gcc behavior.

I posted something similar when the discussion thread started. From the
cursory look, your patch is better than mine. The only difference that
makes me wonder is that I used #ifdef KERN_PROC_SIGTRAMP around the
block because I believe gcc has more relaxed policy about supporting
obsoleted OS versions.

I am aware about KERN_PROC_SIGTRAMP and older OS releases, that's why I asked for feedback. Do we, FreeBSD'ers, want to have gcc unwind support on older than FreeBSD 9.3 releases? I think the gcc folks do not care, but we are the ones who might have an need for such a support?
@Gerald, do you have an opinion?

I can 'ifdef' the new code and in the 'else' case we fall back to the already existing path.

Thank you both for the feedback.

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