xref: /openbsd-src/lib/libc/include/README (revision 8e2ed19fa86ecd0e9ca643bf599ec72da376ab49)

So you want to add an interface to libc...

CASE I: internal symbols

  A) used in a single file
     Duh: use whatever name you want and make it static

  B) used in multiple files
     Give it a name in the implementation namespace (leading underbar)
     and declare it in a __{BEGIN,END}_HIDDEN_DECLS block in a .h
     file inside libc.  If it's used in just a single subdir of
     libc *and* that subdir has an appropriate .h file in it, then
     declare it there.
     Example: stdio/local.h.
     Otherwise, declare it in one of the hidden/* files.
     Example: _mktemp() in hidden/stdio.h

CASE II: external symbols

  First of all, add your symbol to Symbols.list.  MD symbols go in
  arch/*/Symbols.list (shock, I know)

  Declare your function in the appropriate header.  It almost certainly
  should be in a public header installed under /usr/include/.  Exceptions
  are symbols that are just shared between libc and libpthread/csu/ld.so
  which are only declared in libc/include/* or just in each .c file.

  A) objects (variables)
     That's it, you're done.


  B) plain C functions (not syscalls)
     1) functions that are *not* called from inside libc

	If this function is specified in the ISO C standard or its
	name begins with an underbar, then in the hidden/* version
	of the header where you declared the function, add this line:
		PROTO_STD_DEPRECATED(your_function_name);

	Otherwise, this is *not* a function specified in the ISO C
	standard and its name begins with a letter.  In the hidden/*
	version of the header where you declared the function, add
	this line:
		PROTO_DEPRECATED(your_function_name);

	Note: the "DEPRECATED" suffix is about a detail of
	how the macros work and has nothing to do with whether the
	function itself is a Good Thing vs deprecated.

     2) functions that are called from inside libc

	In the hidden/* version of the header where you declared
	the function, add this line:
		PROTO_NORMAL(your_function_name);

	Then, in the .c file(s) where the function is defined:
	 - if the function is specified in the ISO C standard or
	   its name begins with an underbar, add
		DEF_STRONG(your_function_name);

	 - otherwise, add:
		DEF_WEAK(your_function_name);


  C) syscalls that don't require any wrapping

     In the hidden/* version of the header where you declared the
     function, add this line:
	PROTO_NORMAL(your_function_name);

     Generate the stub by adding it to the ASM variable in
     libc/sys/Makefile.inc


  D) syscalls that require cancellation or similar wrappers that don't
     change the function signature

     Generate the stub by adding it to the HIDDEN (*not* ASM!)
     variable in libc/sys/Makefile.inc

     In the hidden/* version of the header where you declared the
     function, add this line:
	PROTO_WRAP(your_function_name);

     The wrapper function should be defined in
	libc/sys/w_your_function_name.c
     which should define WRAP(your_function_name) and follow it
     with DEF_WRAP(your_function_name).  Look at libc/sys/w_sigaction.c
     for an example.

     By default, libc code that calls your_function_name() will get
     the real syscall and *not* the wrapper.  libc calls that need
     to go through the wrapper should invoke WRAP(your_function_name)


  E) syscalls that require libc wrappers for other reasons
     First of all, make sure this really is the Right Thing.  Talk
     with kettenis, deraadt, millert, and guenther.

     If the actual syscall doesn't have the same calling convention
     as the C interface, then maybe it shouldn't be exported at all
     and you should just have an ASM stub, like SYS___tfork -->
     __tfork_thread() or SYS_break --> brk() and sbrk().  If it
     _could_ be called from C, then give the syscall a name different
     from the C API.  Syscalls that fail this for historical reasons
     (e.g., exit == _exit(2)) are generated with PSEUDO/PSEUDO_NOERR
     in libc/sys/Makefile.inc, so the ASM stub has a leading underbar.
     Go read gen/getlogin.c rev 1.13 for an example of how to do
     this, but don't pick this option, really.