bug#24892: {s, }brk removed from FreeBSD 11.x and later, arm64 architecture

[Paul Eggert <eggert@cs.ucla.edu>]

Ashish SHUKLA wrote:

> One of the FreeBSD developer has
> pointed me to this ongoing discussion[1] on freebsd-hackers@ list.
>
> References:
> [1]  https://lists.freebsd.org/pipermail/freebsd-hackers/2016-November/050144.html

OK, thanks, I'll CC: freebsd-hackers. FreeBSD hackers: this is following up on 
this serious Emacs bug report, which says that Emacs no longer works on FreeBSD 
11.x arm64:

https://bugs.gnu.org/24892

The referenced FreeBSD discussion appears to be under the misapprehension that 
sbrk is useful only to estimate how much memory is in use, and since this use 
has long been wrong sbrk should be unceremoniously removed. Unfortunately, this 
assumption is incorrect for Emacs, as (bleeding-edge) Emacs uses its own 
allocator during its build process, and reverts to malloc only during user 
operation. (The build-time Emacs makes a copy of itself in a new executable, and 
relies on sbrk during the build.) Obviously this is dicey and we are planning to 
change Emacs to make it more portable; however, this will require nontrivial 
reengineering on our part.

In the meantime we respectfully request that sbrk functionality be kept in 
FreeBSD 11.x arm64 for a while. It is fine to mark it as deprecated or obsolete, 
or even rename it, but please do not remove the functionality entirely.