Shared Lib Question (ISC)

[John F Haugh II]

In article <1991May10.192648.3147 at Think.COM> barmar at think.com writes:
>In article <19255 at rpp386.cactus.org> jfh at rpp386.cactus.org (John F Haugh II) writes:
>>  Name a single library function
>>which cannot be implemented well without global variables.
>
>Malloc() needs a global variable that points to the arena.
>
>Stdio uses the global variables stdin, stdout, and stderr.
>
>Errno is a global variable, and some library routines set it.

The key word was "well", not "at all".  malloc() can be
implemented as a function which is bound static and has
a single pointer to all the private data that it requires.
It then calls the real routine which takes a pointer to
the arena glarp and size of the desired object.

Likewise for the stdio library.  Functions which have
implied (FILE *) objects can be re-implemented as wrappers
for the versions which require the explicit argument.  The
FILE _iob[] 

Given that the functions were =designed= with the notion
of shared global data, I don't see any reason not to cheat
and leave certain parts =out= of the shared library.

I'll leave errno as an exercise for the reader.

[ Hint: How does the system get errno out of the kernel and
  into the user space, if it is a user space global variable? ]
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