Programmatic use of load module


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Programmatic use of load module

Postby Jeanseb » Sat, 10 Sep 2005 22:09:37 GMT


I have read the windriver tech tip 4179, which explains how to
programmaticaly load modules from RAM/ROM.

I am interested in doing this, since I want to split my code in
multiple modules on my standalone application: updating my code would
only require updating a couple of modules (the link to my standalone
application has a very limited bandwidth). Also at startup, I would be
able to load different modules, and chose which version of my code to

However, I have encoutered 2 major problems:

1) I intend to load code modules from flash from UsrAppInit. There is a
problem though: from UsrAppInit, I cannot invoke any function from the
modules I intend to load, since these functions are not defined in the
scope of the bootable image. I have tried a forward declaration of
these functions (using extern, which works for downloadable
applications) but the code just does not compile ("undefined

2) When modules have a cyclic relationship - Module A invokes Module B,
and Module B invokes Module A - the sequential VxWorks loader does not
work. Since loading Module A first will generate errors due to
undefined symbols from Module B, and vice versa. I have tried to
declare a "fake" module B in module A (create an empty library, used to
register Module B symbols in the symbol table). Then I load module B to
overwrite the fake symbols defined by module A. The idea is to
pre-register module B's symbols when module A is loaded.
possible: "The system symbol table allows name clashes to occur. For
example, suppose a function func exists in the system. A second symbol
named func is added to the system symbol table as part of a load. From
this point, all links to func are to the most recently loaded
symbol...". I have tried multiple options for the loader, but it just
does not work: the symbols defined by module B, even if they use the
same name do not overwrite the fake symbols defined by module A.

Could someone help me please?

Thank you in advance!


Re: Programmatic use of load module

Postby Michael Lawnick » Sat, 10 Sep 2005 22:50:12 GMT

Jeanseb said the following:
You'll have to use function pointer, which you initialize after module load.
Look into symLib to find out how to get the addresses.
No cyclic relation allowed! All symbols must be resolved while download
and won't ever be changed.
If you update a module, unload the old one, load the new one and refresh
the function pointers of the unmodified modules.

!!! Take special care that the processor does not try to call a function
in one of the changed modules while you try to update !!!


Re: Programmatic use of load module

Postby ssubbarayan » Tue, 13 Sep 2005 14:02:35 GMT

eanseb wrote:

There are some info I have gathered from this group which may be
relevant to your query.I am pasting it below for your reference.I
believe it will be of help to you,Though I am not exactly sure how far
this will be solving your query.

Collected info:

I have two VxWorks images in flash. I boot from one of the images. I
I boot from to transfer the second image into RAM and run it. I can
transfer the second image into RAM but I am not sure how to run it.

Can anybody offer any ideas?

Dan J

Michael R. Kesti ( XXXX@XXXXX.COM )
After the second image is loaded into memory (presumably using
or loadModuleAt() ), use symFindByName() to locate that image's entry
and then call the entry point.

Is loadModuleAt() not used for loading .out files? I have a bootable
VxWorks image?
Dan J

Bill Pringlemeir ( XXXX@XXXXX.COM )
This is true. You will have to make a modification to the vxWorks RAM
image. Specifically, you have to look at if it is going to setup
memory mappings. For instance, the RAM image may assume that it is
loaded at a particular memory address. Is the RAM image compressed,
etc. You also didn't mention if the RAM image was pre-built, you are
creating it with the project, or via a makefile.

In any case, there are several possibilities. You jump to the first of
the image. This is usually romInit.s, etc. If the image is not
compressed and just assumes that it is loaded at the right place, then
a jump to "usrInit()" might work. Some images have this address
placed at a fixed offset in the image.

btw, there was no way for Michael to know that you are loading a
binary image versus a elf/coff file. Can you see the need to give
more info?

Bill Pringlemeir.

shafi ( XXXX@XXXXX.COM )
Jump to the starting entry routine location on the second image you
loaded on the RAM. check bootConfig.c sample file. That's what it does
there using a function 'go' to jump and execute the image loaded.
----------------------------- ends here----------------

Query 2:


I am trying to keep my VxWorks image and my application image separate.

Maybe that is really not necessary, but in our product we will quite
be upgrading the application. So I thought it would be a good idea to
the VxWorks image (boot-image), separate from the application.

The problem is: How do I link the VxWorks-image to my application image

my application image is changing all the time?

My plan is to place the application image on the target hard disk. This

provides for easy means for our customers to upgrade to new versions of

application. The VxWorks image will then, in usrAppInit(), perform a
loadModule() to load our application module from disk to memory.

The plan is then to call "MyApplicationStart()". However, I can not
link the
VxWorks image directly to my application, as the application will
over and over again, and thus the address of MyApplicationStart().
I get problems when builing the VxWorks image.

So, what is the best way to achieve this? Could I search for
MyApplicationStart() in the SymTable after performing the loadModule?
Or is
there any other way of linking the VxWorks-image to something that will

dynamically loaded?

Thanks for any help!

Best regards,

Jostein Tro

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