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Name

loadobj, findfn, mysymbols - dynamic object file loader

Synopsis


#include <stdinc.h>
#include <loadobj.h>
void loadobj(string pathname)
proc findfn(string fname)
void mysymbols(string progname)

DescriptionThese routines provide a uniform low-level I/O interface to loading
object modules.  Higher level I/O interfaces are present for a few standard
operations (see e.g. potential(3NEMO) and  bodytrans(3NEMO)). These routines
are intended for applications where a set of mathematical expressions is
specified at runtime as function strings, which are then evaluated for
a large number of variable values. This is done by compiling the set of
function strings into byte code sequences, which can be interpreted very
efficiently for the various variable values.  
The routine mysymbols is generally
called once and in the beginning of the program. It loads all symbols from
the program pointed to by the argument progname, which is normally the
current  program. These symbols are then stored in an internally defined
symbol tree symtree. In case progname is not the complete name, the PATH
environment variable is used (see pathopen(3NEMO)). 
The undefined symbols
in each object module that is loaded with  loadobj are resolved against
the already existing symbol tree,  and new symbols are added to the tree.
If a symbol is not found to be resolved, this is considered an error, and
error(3NEMO) is called, which aborts the program. In addition the code loaded
into memory is properly relocated using information in the object code.
The argument pathname must be the proper filename, no search path is provided
for. 
After all symbols have been defined, the programmer can obtain pointers
to functions which is specified by name using findfn. 
ExampleIn the following
section of code gives an example of use. 
    proc fn;                   /* see defs in <stdinc.h> */
    mysymbols(getparam("argv0"));   /* get local symbols */
    loadobj("test.o");               /* load object code */
    fn = (proc) findfn("_test");       /* find function  */
    if (fn==NULL) error("No test");       /* catch error */
    (*fn)();         /* execute routine test() in test.o */

See Also

a.out(4) , potential(3NEMO) , bodytrans(3NEMO) ), dlopen(3) , dyld(3)

Author

Eric Roberts (original SunOS version), Peter Teuben (sun4, coff, dl)

Files


~/src/kernel/loadobj         loadobj.c, loadobj*.c
Much like yapp(3NEMO) , different implementations exist for different operating systems.

Update History


23-jul-90       created         PJT
6-nov-91    slight doc improvements; loadobjNEXT.c       PJT
30-jun-03    documented mach's dyld        PJT

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