Re: glibc 2.24 -- Release blockers

[Paul Eggert <eggert at cs dot ucla dot edu>]

On 07/15/2016 11:19 PM, Zack Weinberg wrote:
> Emacs' bundled malloc assumes that the data
> segment is contiguous with, or at least close to, the memory region
> controlled by brk().  This is not true with ASLR enabled, on certain
> architectures (e.g. ppc64).

Unfortunately Emacs with glibc 2.22 malloc seems to be making the 
opposite assumption, at least on Fedora 23 x86-64. That is, if I disable 
ASLR in an ordinary (dumped) Emacs with glibc 2.22, Emacs stops working 
(I don't know why). This leads me to be leery of disabling ASLR in an 
ordinary Emacs, except for platforms like ppc64 where it seems to be 
necessary. The patch I just sent in therefore has a special case for 
__PPC64__. Quite a hack, but without knowing the problem better I don't 
know what other hack to try.

> It looks like
> HYBRID_MALLOC mode would avoid the problem, but from upthread, that
> mode isn't ready for prime time yet...?


Yes, my sense is that HYBRID_MALLOC should work but it is not ready for 
emacs-25. It is already enabled in the master branch and we should be 
able to get it to work with ppc64 too, at least assuming the patch I 
just emailed here works on emacs-25.