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This directory contains examples of source code that can be loaded
during fudgit running time.
So far, dynamic loading option is supported by IRIX, ULTRIX (on vax)
and SUNOS.
This contains short examples of dynamic loading. Note that install
does not check for the source to be compiled. The user is responsible
for compiling the object.
In C:
On IRIX, you must compile mymodule.c using -G 0 absolutely.
(Edit the Makefile to take care of this.)
cc -G 0 -O -c mymodule.c
Read the script mymodule.ft and the program mymodule.c for more detail.
In FORTRAN:
On IRIX, you must compile mysubs.f using -G 0 absolutely.
(Edit the Makefile to take care of this.)
f77 -G 0 -O -c mysubs.f
Read the script mysubs.ft and the program mysubs.f for more detail.
File mysubs.libs is an example of how to proceed to link/load external
libraries.
-------------------------------------------------------------------
The following NOTES are adapted sections of the man pages of 'dl'
package. Read carefully the part on linking with extra libraries (G0).
This applies to IRIX O N L Y!
----
If there is a file with the same name as the object file,
but with extension .libs this file is assumed to contain
command-line options to ld(1). This feature can be used if
the object needs to be linked with special libraries, for
instance.
Because linking the object is a fairly time-consuming pro-
cess the resulting binary is cached with extension .ld . The
version stamp of the cached binary is set on a number com-
puted from the time stamps of both the object file and the
running executable. Before linking 'install' checks
whether a cached binary exists and whether the load address
and version stamp match the required values. If so, it skips
the link phase.
If there is no cached binary or if the version stamp and
load address do not match 'install' attempts to create the
cached binary. If it cannot do this, due to lack of permis-
sion, for instance, it will create a temporary binary in
/usr/tmp .
NOTES
The object file (and all libraries used) should be compiled
with the -G 0 flag. The linker could probably check this but
does not, unfortunately. Not compiling your subroutine with
-G 0 or using a library that is not compiled with -G 0 will
result in wondrous and deeply puzzling results from your
program. SGI provides versions of all libraries compiled
with -G 0, these have a _G0 suffix, as in -lc_G0. Shared
libraries are also safe.
Using a set of routines that uses global data (like stdio)
will work, whether the routines are used in the main execut-
able or not. What will not work, however, is using some-
thing like stdio in more than one dynamically loaded module
when it is not used in the main executable (because each
dynamic module will have its own copy of the global data).
There may be other subtleties involved with shared
libraries, global data structures or other features like
sproc(2) that I am not aware of.
Although the package has support for incremental loading
this does not work currently, due to ld(1) refusing to take
the output of an incremental link as the input to another
incremental link.
BUGS
The algorithm used to locate unused virtual memory may fail
if the program does mmap(2) or shmat(2) calls.
Temporary binaries created in /usr/tmp are only removed if
FUDGIT exits normally.
Incremental loading is a bit of a hack: the loaded modules
are patched to remove definitions of _end, _etext and
_edata. This might affect some programs adversely since the
value of those symbols will be different in different
modules.
Error messages issued by the ldfcn(3) library or by the
linker always end up on stderr.
FILES
object.o
object.dl
object.libs
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