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Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?
From: |
Doug Moore |
Subject: |
Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it? |
Date: |
Wed, 29 Mar 2017 15:48:53 -0500 |
For linux, it’s not using the ip directly to determine is_signal_frame, but
it’s using information from processing dwarf data, which it can only find if it
has the right ip in the first place.
It seems like the init_cursor caller should be passing an argument to declare
whether this is a signal handler frame or not. I’d expect her to know that.
It’s a lot more reliable that having libunwind try to figure it out.
Doug
> On Mar 29, 2017, at 3:33 PM, Doug Moore <address@hidden> wrote:
>
>> But I think we need to know the IP to detect signal frames?
>
>
> We need to know an IP, yes. It’s not clear that we need the decremented-by-1
> IP, though. Especially since we’re deciding whether to decrement it based on
> whether it’s in a signal frame or not.
>
> I looked at the x86_64 implementations of unw_is_signal_frame for freebsd and
> linux.
>
> For freebsd, unw_is_signal_frame uses the (unmodified) ip in the cursor
> argument to determine whether this is a signal frame. So, for freebsd, we
> could call unw_is_signal_frame early, passing the cursor we had already, and
> use that to determine whether or not to use ip or ip-1 for searching
> dwarf/eh_frame structures.
>
> For linux, unw_is_signal_frame does not look at the ip; it returns a value
> under the assumption that another function, either tdep_fetch_frame or
> tdep_cache_frame, has already set that value. And tdep_fetch_frame does not
> look at the ip field of the cursor passed to it either. Really, I’m not sure
> yet where the ip gets examined in the linux version of unw_is_signal_frame.
>
> Doug
>
>
>> On Mar 29, 2017, at 10:12 AM, Dave Watson <address@hidden> wrote:
>>
>> On 03/27/17 05:36 PM, Doug Moore wrote:
>>> It looks like the call to tdep_fetch_frame in fetch_proc_info would
>>> determine whether or not this was a signal frame, and thus whether or not
>>> we needed to use the previous instruction for the lookup.
>>>
>>> Of course, we call tdep_fetch_frame only after we’ve already tried that
>>> lookup. But perhaps some of the work done to identify signal frames could
>>> be moved up a bit, so that a better decision could be made about whether or
>>> not to use the previous instruction.
>>>
>>> Does that make any sense?
>>
>> But I think we need to know the IP to detect signal frames?
>>
>> My thought was that if IP-1 lookup failed, we could try IP lookup, and
>> if it was a signal frame, use that instead (probably with verify=1)
>>
>> !DSPAM:10223,58dbcee539347198113515!
>>
>>
>
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, (continued)
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Lassi Tuura, 2017/03/24
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Doug Moore, 2017/03/24
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Doug Moore, 2017/03/24
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Lassi Tuura, 2017/03/26
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Doug Moore, 2017/03/26
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Dave Watson, 2017/03/27
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Dave Watson, 2017/03/27
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Doug Moore, 2017/03/27
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Dave Watson, 2017/03/29
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Doug Moore, 2017/03/29
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?,
Doug Moore <=
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Doug Moore, 2017/03/29
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Dave Watson, 2017/03/30
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Doug Moore, 2017/03/30
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Doug Moore, 2017/03/30
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Dave Watson, 2017/03/30
- Re: [Libunwind-devel] use_prev_instr breaking unwind - how to stop it?, Doug Moore, 2017/03/30