DDE legacy kernel module as library

Andre Puschmann andre.puschmann at imms.de
Wed Feb 18 13:40:16 CET 2009

Hi Michael,

Michael Roitzsch schrieb:
> When creating the final binary, the linker has the habit of throwing 
> code out it considers unused. For library constructors, this can go 
> wrong, because the calls to them are generated only at runtime and are 
> thus not visible to the linker, which then wrongly concludes to drop them.
> The fix (actually it's more of a workaround) is to rename the static 
> library in the Makefile TARGET from libdriver.a to libdriver.o.a. This 
> causes the build system to combine the individual objects into one large 
> object instead of a regular static library archive. You can later link 
> to that lib with -ldriver.o as expected.
> The effect is that the linker cannot throw code out of such a lib, 
> because to it, this is essentially one large object file and the GNU 
> linker only drops code with object granularity. (So this uses one 
> peculiarity of the GNU linker to fix another one.)

Ack. Thanks for that hint. Your proposal works like a charm.
Here is another solution: I wrote a small "hello-world" Linux kernel 
module with just two functions: init_module() and exit_module().
I thought that would be enough for demonstration. My fault. The linker 
needs at least one _real_ reference. So adding a further print_hello() 
function to the module and a call to that function from within my L4 
server fixed the whole problem. Now, I see DDE calling my init function.

Thanks very much.


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