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Re: Critical bytecode bug with hash tables while dumping emacs.

From: Vibhav Pant
Subject: Re: Critical bytecode bug with hash tables while dumping emacs.
Date: Fri, 27 Jan 2017 13:45:57 +0000

Also, this one line patch crashes temacs with a SIGSEGV - the hash table contents
are possibly getting corrupted because of a bad memory write.

On Fri, Jan 27, 2017 at 12:27 AM Vibhav Pant <address@hidden> wrote:
On Thu, Jan 26, 2017 at 11:03 PM, Paul Eggert <address@hidden> wrote:
> In that case the bug is not critical, right? One way to address the problem
> is to say that code should not print hash tables before dumping.

It's critical in the sense that any code loaded from loadup.el is effectively
prohibited from using printed hash tables in any way. I've recently been
working on adding a new 'switch` bytecode op (@ branch feature/byte-switch),
which uses hash tables generated during compile time (so the constant vector
stores printed hash tables) as jump tables. This bug breaks switch entirely.

> we're planning to redo dumping anyway and can address this problem (if it still
> occurs) then.

I suspect this bug is related to purecopy, which I suppose isn't a part of the
redo (or is it? I don't know much about the new dumping code). If anyone has any
ideas about this issue, I'd appreciate some pointers on where to start.

Vibhav Pant

Attachment: wrong-hash-table.patch
Description: Text Data

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