libc : non-c specific functions!

[Polytropon]

On Wed, 16 Jan 2019 05:05:08 GMT, iam at sdf.org wrote:
> is there any way to find out which functions in libc are non-c
> specific, so for example if i had to implement a syslib in
> assembly language, i could just avoid the "c" parts as they
> would be irrelevant.

Everything that's in the standard C library is stuff required
by the C standard. It doesn't actually matter _how_ it is
implemented, even though it's commonly implemented in C.
So "nothing and everything is C-specific". ;-)

Your question is a bit strange (or I'm just too stupid to
understand it correctly).

Allow me to explain:

The libc isn't there for its own good. It's a library used
by other programs which call functions from that library
using those function names, after linking to that library,
simplified speaking. If you would implement your alternative
system library, let's say libsys, and let's say you do this
in assembly, then no other program could use it _except_ you
implement the calling interface (i. e.,  its API) in the
exact same way. This is the only way other programs could
use it instead of libc.

Example: You want a non-libc equivalent of dmesg. You start
by examining /usr/src/sbin/dmesg/dmesg.c, which header files
does it include? Which libc calls does it make? Your libsys
would heed to implement them - _how_ it does that is of no
interest to the compiler / linker. So after you've done that,
you could recompile "cc -lsys <more stuff> -o dmesg dmesg.c"
and it would no longer need libc.

On the other hand, if you're going to develop your own (!)
userland tools, based upon your own libsys written in assembly,
you can create your own new universe, as long as compatibility
is not required.

FreeBSD's implementation of libc is in /usr/src/lib/libc and
its subdirectories. Even though the standard C library is a
very common thing, it's implemented differently on the many
existing operating systems, and even its name can be different,
for example glibc (GNU libc) on Linux. The content can also
be different, as the C standard requires certain things, but
the library maintainer could decide to add other things, for
example POSIX extensions (which are not required by the C
standard).




-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...