Re: [Libunwind-devel] [PATCH] Add an option to have start_ip_offset be relative to start_ip

[Keno Fischer]

I suspect it is a problem for you guys as well (unless you do your own memory allocation and force things to be close together). In particular, I wouldn't be surprised if you ran into problems if you put a safe trunc on this line (that's a cursory guess, I haven't actually tested that):

https://github.com/dropbox/pyston/blob/60bab2eabd25f745c15eb967a7fd7d778581b9bc/src/codegen/unwinding.cpp#L92

Do you guys use no-fp-elim in LLVM? libunwind is pretty good about figuring stuff out in those cases, so you may just not have noticed.

I will update the patch to address the review comments.

On Tue, Oct 6, 2015 at 6:27 PM, Kevin Modzelewski <address@hidden> wrote:

On Tue, Oct 6, 2015 at 10:20 AM, Arun Sharma <address@hidden> wrote:

On Sun, Oct 4, 2015 at 10:30 PM, Keno Fischer
<address@hidden> wrote:
> Bump, does this patch look reasonable?

Yes - looks reasonable to me. Wonder why it wasn't a problem for other
LLVM JIT users (eg: pyston?).

Now I'm curious too :)  Though I don't think our eh_frame and text sections are that far apart.  tbh I don't have a great understanding of the interaction between MCJIT and libunwind; for instance it also seems odd that the format that works is REMOTE_TABLE and not (non-remote) TABLE.

 

> unw_dyn_remote_table_t, but

I think you meant to say "Like REMOTE_TABLE, but ..".

Perhaps call it IP_OFFSET instead of TABLE2?

+  if (di->format == UNW_INFO_FORMAT_REMOTE_TABLE ||
+      di->format == UNW_INFO_FORMAT_REMOTE_TABLE2)

Could you wrap this in is_remote_table()?

> +    ip_base = segbase;

Rename it something neutral that works for both the segbase and ip_base cases?

 -Arun

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