From: Florian Weimer <fweimer@redhat.com>
To: Nathan Sidwell <nathan@acm.org>, GCC <gcc@gcc.gnu.org>,
GNU C Library <libc-alpha@sourceware.org>,
Binutils <binutils@sourceware.org>,
gnu-gabi@sourceware.org
Subject: Re: Invalid program counters and unwinding
Date: Tue, 26 Jun 2018 11:21:00 -0000 [thread overview]
Message-ID: <8a147f05-509f-16a0-f108-9e76bcae4ea9@redhat.com> (raw)
In-Reply-To: <0b0e49f0-7ed0-aa4e-a4df-d4286206dab5@acm.org>
On 06/26/2018 01:15 PM, Nathan Sidwell wrote:
> On 06/26/2018 07:01 AM, Florian Weimer wrote:
>> On 06/26/2018 12:56 PM, Nathan Sidwell wrote:
>>> On 06/26/2018 05:26 AM, Florian Weimer wrote:
>>>
>>>> So it looks to me that the caller of _Unwind_Find_FDE needs to
>>>> ensure that the PC is a valid element of the call stack. Is this a
>>>> correct assumption?
>>>
>>> I thought this was an (implicit?) requirement. You're unwinding a
>>> stack to deliver an exception up it. Are there use cases where that
>>> is not the case?
>>
>> We have something approaching this scenario.
>>
>> pthread_cancel in glibc unwinds the stack using DWARF information
>> until encounters a frame without unwind information, when it switches
>> to longjmp to get past that obstacle.
>
> This is a long jump to the originating pthread function at the end of
> the stack, right? We not only get past the obstacle, but any and all
> DWARF frames on top of it. (just for my understanding)
Essentially yes. It can also be an intermediate jump buffer, used to to
support compilation in -fno-exceptions mode. In that case, unwinding
tries to proceed from there, again with a valid PC.
> That sounds right. It's a PC that you could return to if you weren't trying to unwind the stack.
GCC doesn't do this AFAIK, but it's theoretically possible not to
preserve the return address for a noreturn function. But that would be
very bad for exception handling, so let's hope compilers don't do this.
Florian
next prev parent reply other threads:[~2018-06-26 11:21 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-26 9:26 Florian Weimer
2018-06-26 10:56 ` Nathan Sidwell
2018-06-26 11:01 ` Florian Weimer
2018-06-26 11:15 ` Nathan Sidwell
2018-06-26 11:21 ` Florian Weimer [this message]
2018-06-26 11:35 ` Nathan Sidwell
2018-06-26 11:39 ` Florian Weimer
2018-06-26 11:46 ` Jakub Jelinek
2018-06-26 11:46 ` Nathan Sidwell
2018-06-26 11:25 ` Jakub Jelinek
2018-06-26 11:31 ` Florian Weimer
2018-06-28 2:16 ` Jeff Law
2018-06-28 12:31 ` Florian Weimer
2018-06-28 14:18 ` Jeff Law
2018-06-28 14:49 ` Florian Weimer
2018-07-02 15:48 ` Michael Matz
2018-07-02 15:54 ` Jakub Jelinek
2018-07-02 16:14 ` Michael Matz
2018-07-05 19:31 ` Florian Weimer
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