From: Florian Weimer <fweimer@redhat.com>
To: Jeff Law <law@redhat.com>, 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: Mon, 01 Jan 2018 00:00:00 -0000 [thread overview]
Message-ID: <373e6dbe-47f9-9f49-56e9-4bdc5474f7aa@redhat.com> (raw)
In-Reply-To: <6c555c05-e6d7-f37a-577f-4e0559c36f76@redhat.com>
On 06/28/2018 04:18 PM, Jeff Law wrote:
> On 06/28/2018 06:30 AM, Florian Weimer wrote:
>> On 06/28/2018 04:16 AM, Jeff Law wrote:
>>>> Previous discussions:
>>>>
>>>> https://gcc.gnu.org/ml/gcc/2013-05/msg00253.html
>>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71744
>>>> https://sourceware.org/ml/libc-alpha/2016-07/msg00613.html
>>>> Â Â (patch with a spread lock, still not async-signal-safe)
>>
>>> You might also want to look at RH BZ 1293594 which I think has pointers
>>> back to an issue from 2008 :(
>>
>> Interesting. That does suspiciously look like a concurrent dlclose.
>> It's just that the crash handler crashes, after the application crash. I
>> think this one is really NOTABUG, both technically and from user impact:
>> we do not cause the crash, we just react poorly to the application
>> triggering undefined behavior.
>>
>> In the bug, you mentioned this code fragment for x86-64:
>>
>> 42Â Â Â Â Â Â Â unsigned char *pc = context->ra;
>> 43Â Â Â Â Â Â Â struct sigcontext *sc;
>> 44Â Â Â Â Â Â Â long new_cfa;
>> 45
>> 46       /* movq __NR_rt_sigreturn, %rax ; syscall */
>> 47Â Â Â Â Â Â Â if (*(unsigned char *)(pc+0) == 0x48
>> 48Â Â Â Â Â Â Â Â Â Â Â && *(unsigned long *)(pc+1) == 0x050f0000000fc0c7)
>>
>> I'm not sure I agree that it is âdumbâ, but I think it proves
>> conclusively that you cannot feed random addresses to the unwinder. 8-)
> I believe "dumb" is referring to the fact that we're already in a bit of
> a weird state as evidenced by the NULL FDE. Blindly trying to read the
> contents of the PC that we couldn't map to an FDE is, IMHO, dumb.
I think the code derives from i386, where historically it was necessary
to unwind with the frame pointer only. I suspect we still need this
code there at least, to support legacy binaries.
For x86-64, we should probably not to attempt without tables at all, but
I have no idea whether that's feasible.
Thanks,
Florian
next prev parent reply other threads:[~2018-06-28 14:49 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-01 0:00 Florian Weimer
2018-01-01 0:00 ` Jeff Law
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Jeff Law
2018-01-01 0:00 ` Florian Weimer [this message]
2018-01-01 0:00 ` Michael Matz
2018-01-01 0:00 ` Jakub Jelinek
2018-01-01 0:00 ` Michael Matz
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Nathan Sidwell
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Jakub Jelinek
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Nathan Sidwell
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Nathan Sidwell
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Nathan Sidwell
2018-01-01 0:00 ` Jakub Jelinek
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