Portability Question

[Evan Klitzke]

I am (hopefully) a new Emacs contributor and I started working on some 
changes to Emacs that I would like to contribute as patches, and I have 
some questions about writing platform specific code in Emacs. I'm adding 
new code in sysdep.c and want to know the best practices.

The first question I have is which standard POSIX headers it's safe to 
assume are available. The reason I ask this is that sysdep.c already 
includes <unistd.h> without a HAVE_UNISTD_H check, which implies to me 
that there's already a requirement on having POSIX headers available 
(i.e. I assume on Windows Cygwin is required to build?). But, somewhat 
confusingly, when sysdep.c includes <pwd.h> it uses a HAVE_PWD_H guard, 
even though this is a standard POSIX header.

Another question I have is: in practice, which build configurations for 
Emacs are likely to link against glibc vs another libc (e.g. I see there 
are a number of checks to see if __UCLIBC__ is defined, so at a minimum 
that's a possibility). For example, do the various macos builds (e.g. 
emacsformacosx.com and homebrew) typically use glibc or the macos system 
libc? And same question for Windows. The reason I'm asking is if I 
opportunistically want to use a glibc extension and fallback to 
something that works but is hacky if glibc isn't available, I'm 
wondering in practice which build configurations will have to use the 
hacky fallback path.

Thanks much.

P.S. I need to sign an FSF copyright assignment agreement (as an 
individual contributor). Can someone send me the necessary documents?

--
Evan Klitzke                      pgp: 0x157EFCACBC648422
e: address@hidden              w: https://eklitzke.org