Re: Crash robustness (Was: Re: Dynamic modules: MODULE_HANDLE_SIGNALS etc.)

[Daniel Colascione <dancol@dancol.org>]

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On 12/23/2015 09:55 AM, Eli Zaretskii wrote:
>> Cc: eggert@cs.ucla.edu, aurelien.aptel+emacs@gmail.com,
>>  p.stephani2@gmail.com, tzz@lifelogs.com, emacs-devel@gnu.org
>> From: Daniel Colascione <dancol@dancol.org>
>> Date: Wed, 23 Dec 2015 09:41:20 -0800
>>
>>> We could try calling shut_down_emacs from the signal handler, but I'm
>>> not sure if the small alternate stack will be enough for write-region.
>>> Something to investigate, I guess.
>>
>> We can make the alternate signal stack as large as we want.
> 
> Not as large as is safe to run arbitrary Lisp.

Then don't run arbitrary lisp after we've segfaulted.

> 
>>>> The next time Emacs starts, we can restore the buffers we've saved
>>>> this way and ask users to save them --- just like autosave, but done
>>>> on-demand, at crash time, in C code, on the alternate signal stack.
>>>
>>> Why "like autosave"?  What will be different from actually
>>> auto-saving?  shut_down_emacs does that automatically.
>>>
>>
>> Er, yes, I noticed that after I wrote the email that we already do what
>> I propose, more or less. In this case, we don't lose very much by just
>> deleting the stack overflow code and relying on autosave.
> 
> Auto-save will only save buffers that visit files.
> 

A minimal, C-only autosave run in the signal-handling path could save
all buffer content.


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