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kern/51654: wrong ps_strings breaks emacs20
>Synopsis: wrong ps_strings breaks emacs20
>Arrival-Date: Sat Nov 26 04:00:00 +0000 2016
>Originator: David A. Holland
>Release: NetBSD 7.99.42 (20161125)
System: NetBSD valkyrie 7.99.42 NetBSD 7.99.42 (VALKYRIE) #20: Fri Nov 25 18:33:19 EST 2016 dholland@valkyrie:/usr/src/sys/arch/amd64/compile/VALKYRIE amd64
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
I stuck some debugging code into a copy of _libc_init and inserted it
with LD_PRELOAD, and found that __ps_strings is 0x7f7fffffffe0 while
the highest valid range in the address space in /proc/pid maps is
00007f7fffff0000-00007f7ffffff000 rw-p 0000000000000000 00:00 0
..................... 0x7f7fffffffe0 is off the end.
It looks to me like this is because the kernel is providing the wrong
ps_strings address, not because ld.elf_so is mucking about and
garbaging the value, but it's hard to tell because even at its most
verbose ktrace doesn't record this information. (That is itself a bug
and should get fixed.)
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.
You can build a new emacs binary that exhibits the same behavior as my
old one by building editors/emacs20-20.7nb21 (which I just committed,
with fixes for some other problems) on current amd64. Or at least, I
can. YMMV, but hopefully it's not just me.
Not being able to run my editor is making it rather difficult to do
stuff, so I'd appreciate help...
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