Move the trampolines for dlopen and related functions from crt0.o

into libc.  This reduces the size of every dynamically linked
executable by 248 bytes, and it reduces the size of static executables
by a lesser amount.  It also eliminates some global namespace
pollution.

With this change in place, the source for dlfcn.h should probably
be moved to "/usr/src/include".  I'll save that for another day.

Compatibility note:  Programs which use dlopen, if compiled on
systems with this change, will not run on systems with a libc from
prior to this change.  Very few programs use dlopen, so I think
that is OK.

1 files changed, 236 insertions, 0 deletions

diff --git a/lib/libc/gen/dlopen.3 b/lib/libc/gen/dlopen.3
new file mode 100644
index 0000000..b9a987c
--- /dev/null
+++ b/lib/libc/gen/dlopen.3
@@ -0,0 +1,236 @@
+.\" This source code is a product of Sun Microsystems, Inc. and is provided
+.\" for unrestricted use provided that this legend is included on all tape
+.\" media and as a part of the software program in whole or part.  Users
+.\" may copy or modify this source code without charge, but are not authorized
+.\" to license or distribute it to anyone else except as part of a product or
+.\" program developed by the user.
+.\"
+.\" THIS PROGRAM CONTAINS SOURCE CODE COPYRIGHTED BY SUN MICROSYSTEMS, INC.
+.\" SUN MICROSYSTEMS, INC., MAKES NO REPRESENTATIONS ABOUT THE SUITABLITY
+.\" OF SUCH SOURCE CODE FOR ANY PURPOSE.  IT IS PROVIDED "AS IS" WITHOUT
+.\" EXPRESS OR IMPLIED WARRANTY OF ANY KIND.  SUN MICROSYSTEMS, INC. DISCLAIMS
+.\" ALL WARRANTIES WITH REGARD TO SUCH SOURCE CODE, INCLUDING ALL IMPLIED
+.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN
+.\" NO EVENT SHALL SUN MICROSYSTEMS, INC. BE LIABLE FOR ANY SPECIAL, INDIRECT,
+.\" INCIDENTAL, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
+.\" FROM USE OF SUCH SOURCE CODE, REGARDLESS OF THE THEORY OF LIABILITY.
+.\" 
+.\" This source code is provided with no support and without any obligation on
+.\" the part of Sun Microsystems, Inc. to assist in its use, correction, 
+.\" modification or enhancement.
+.\"
+.\" SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE
+.\" INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS
+.\" SOURCE CODE OR ANY PART THEREOF.
+.\"
+.\" Sun Microsystems, Inc.
+.\" 2550 Garcia Avenue
+.\" Mountain View, California 94043
+.\"
+.\" Copyright (c) 1991 Sun Microsystems, Inc.
+.\"
+.\" @(#) dlopen.3 1.6 90/01/31 SMI
+.Dd September 24, 1989
+.Os FreeBSD
+.Dt DLOPEN 3
+.Sh NAME
+.Nm dlopen, dlsym, dlerror, dlclose
+.Nd programmatic interface to the dynamic linker
+.Sh SYNOPSIS
+.Fd #include <dlfcn.h>
+.Ft void *
+.Fn dlopen "const char *path" "int mode"
+.Ft void *
+.Fn dlsym "void *handle" "const char *symbol"
+.Ft const char *
+.Fn dlerror "void"
+.Ft int
+.Fn dlclose "void *handle"
+.Sh DESCRIPTION
+These functions provide a simple programmatic interface to the services of the
+dynamic linker.
+Operations are provided to add new shared objects to a
+program's address space, to obtain the address bindings of symbols
+defined by such
+objects, and to remove such objects when their use is no longer required.
+.Pp
+.Fn dlopen
+provides access to the shared object in 
+.Fa path ,
+returning a descriptor that can be used for later
+references to the object in calls to 
+.Fn dlsym
+and
+.Fn dlclose .
+If
+.Fa path
+was not in the address space prior to the call to
+.Fn dlopen ,
+it is placed in the address space.
+When an object is first loaded into the address space in this way, its
+function
+.Fn _init ,
+if any, is called by the dynamic linker.
+(Note that
+.Ql _init
+is the name as expressed in the C language.
+From assembly language, the name would appear as
+.Ql __init
+instead.)
+If
+.Fa path
+has already been placed in the address space in a previous call to
+.Fn dlopen , 
+it is not added a second time, although a reference count of 
+.Fn dlopen
+operations on
+.Fa path
+is maintained.
+A null pointer supplied for 
+.Fa path
+is interpreted as a reference to the main
+executable of the process.
+.Fa mode
+controls the way in which external function references from the
+loaded object are bound to their referents.
+It must contains one of the following values:
+.Bl -tag -width RTLD_LAZYX
+.It Dv RTLD_LAZY
+Each external function reference is resolved when the function is first
+called.
+.It Dv RTLD_NOW
+All external function references are bound immediately by
+.Fn dlopen .
+.El
+.Pp
+.Dv RTLD_LAZY
+is normally preferred, for reasons of efficiency.
+However,
+.Dv RTLD_NOW
+is useful to ensure that any undefined symbols are discovered during the
+call to
+.Fn dlopen .
+If 
+.Fn dlopen
+fails, it returns a null pointer, and sets an error condition which may
+be interrogated with
+.Fn dlerror .
+.Pp
+.Fn dlsym
+returns the address binding of the symbol described in the null-terminated
+character string
+.Fa symbol ,
+as it occurs in the shared object identified by
+.Fa handle .
+Note that
+.Fa symbol
+is the assembly language representation of the symbol name.
+The assembly language representation of a C language symbol contains an
+extra underscore at the beginning.
+For example, the symbol
+.Ql foo
+in C would appear as
+.Ql _foo
+in assembly language, and in the
+.Fa symbol
+argument to
+.Fn dlsym .
+The symbols exported by objects added to the address space by 
+.Fn dlopen
+can be accessed only through calls to
+.Fn dlsym .
+Such symbols do not supersede any definition of those symbols already present
+in the address space when the object is loaded, nor are they available to
+satisfy normal dynamic linking references.
+A null pointer supplied as the value of 
+.Fa handle
+is interpreted as a reference to the executable from which the call to 
+.Fn dlsym
+is being made.  Thus a shared object can reference its own symbols.
+.Fn dlsym
+returns a null pointer if the symbol cannot be found, and sets an error
+condition which may be queried with
+.Fn dlerror .
+.Pp
+If
+.Fn dlsym
+is called with the special
+.Fa handle
+.Dv RTLD_NEXT ,
+then the search for the symbol is limited to the shared objects
+which were loaded after the one issuing the call to
+.Fn dlsym .
+Thus, if the function is called from the main program, all
+the shared libraries are searched.
+If it is called from a shared library, all subsequent shared
+libraries are searched.
+.Dv RTLD_NEXT
+is useful for implementing wrappers around library functions.
+For example, a wrapper function
+.Fn getpid
+could access the
+.Dq real
+.Fn getpid
+with
+.Li dlsym(RTLD_NEXT, \&"_getpid\&") .
+.Pp
+.Fn dlerror
+returns a null-terminated character string describing the last error that
+occurred during a call to
+.Fn dlopen ,
+.Fn dlsym ,
+or
+.Fn dlclose .
+If no such error has occurred,
+.Fn dlerror
+returns a null pointer.
+At each call to
+.Fn dlerror ,
+the error indication is reset.  Thus in the case of two calls
+to
+.Fn dlerror ,
+where the second call follows the first immediately, the second call
+will always return a null pointer.
+.Pp
+.Fn dlclose
+deletes a reference to the shared object referenced by
+.Fa handle .
+If the reference count drops to 0, the object is removed from the
+address space, and
+.Fa handle
+is rendered invalid.
+Just before removing a shared object in this way, the dynamic linker
+calls the object's
+.Fn _fini
+function, if such a function is defined by the object.
+As with
+.Ql _init ,
+.Ql _fini
+is the C language name of the function.
+If 
+.Fn dlclose
+is successful, it returns a value of 0.
+Otherwise it returns -1, and sets an error condition that can be
+interrogated with
+.Fn dlerror .
+.Pp
+The object-intrinsic functions 
+.Fn _init
+and
+.Fn _fini
+are called with no arguments, and are not expected to return values.
+.Sh ERRORS
+.Fn dlopen
+and
+.Fn dlsym
+return the null pointer in the event of errors.
+.Fn dlclose
+returns 0 on success, or -1 if an error occurred.
+Whenever an error has been detected, a message detailing it can be
+retrieved via a call to
+.Fn dlerror .
+.Sh SEE ALSO
+.Xr ld 1 ,
+.Xr rtld 1 ,
+.Xr link 5
+