Re: kern/51654: wrong ps_strings breaks emacs20

[David Holland <dholland-bugs%netbsd.org@localhost>]

The following reply was made to PR kern/51654; it has been noted by GNATS.

From: David Holland <dholland-bugs%netbsd.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/51654: wrong ps_strings breaks emacs20
Date: Sat, 26 Nov 2016 06:14:39 +0000

 On Sat, Nov 26, 2016 at 05:50:01AM +0000, Joerg Sonnenberger wrote:
  >  On Sat, Nov 26, 2016 at 04:00:00AM +0000, dholland%NetBSD.org@localhost wrote:
  >  > After updating emacs dumps core. After spending a long time barking up
  >  > the wrong PaX tree, it seems that the problem is that an invalid
  >  > pointer is being provided in __ps_strings and this causes _libc_init
  >  > to segv.
  >  
  >  The address space layout changed. ps_strings is placed at the very top,
  >  without PAX it is at a fixed address.
 
 Turning off aslr with paxctl has no effect.
 
  >  > I haven't the slightest idea why this happens only with emacs but I
  >  > imagine it's a consequence of the emacs dump/undump mechanism somehow.
  >  
  >  Combine this with the changed MAXUSER address and now certain cached
  >  locations no longer match.
 
 Cached in what? The value for __ps_strings is provided by the kernel
 to crt0 and propagates to _libc_init (and causes it to croak) before
 anything in emacs gets control.
 
 -- 
 David A. Holland
 dholland%netbsd.org@localhost