Re: [Linux-ia64] Re: loading a kernel module

[Keith Owens <kaos@ocs.com.au>]

On Wed, 16 Oct 2002 07:52:15 +0200, 
Christian Hildner <christian.hildner@hob.de> wrote:
>the source isn't that complex as you might have seen in the length of the objdump output.
>The object I have given you is only a small test program to find out the missing linkage for
>brl branches. My original program needs brl to branch across virtual pages with a big
>difference in the virtual addresses. So the test prog never makes any sence, but shows the
>missing R_IA64_PCREL60B nicely.
>
>Christian
>
>PS: Here is the source without any guarantee not to crash ...
>
>#define MODULE
>#include <linux/module.h>
>
>int dummy(void)
>{
>    return 0;
>}
>
>int init_module(void)
>{
>    printk("Init Module starting. About to crash...\n");
>    asm volatile ("brl dummy ");
>    return 0;
>}
>
>void cleanup_module(void)
>{
>    printk("Done\n");
>}

OK, so it is not a toolchain problem, this is user code.  Unfortunately
it is introducing a special case into modutils.

All existing PCREL relocations in modutils go via a PLT, saving and
switching GP as they do so.  I am assuming that branching via the PLT
is no good for you, you really do want a direct branch over the 64 bit
address space, without any change to GP.  That is, the source and
target addresses use the same global data area, or one of them does not
use any global data area at all.  Please confirm this before I make any
changes.

If you need different GP values in the source and target addresses then
a normal PCREL21 via PLT will do the job.