ld relocation problem on ARM (PIC related)

[jeroen dobbelaere]

Daniel Jacobowitz wrote:
> On Wed, Nov 06, 2002 at 05:24:38PM +0100, jeroen dobbelaere wrote:
> 
[...]
>>At 0x83e4, 'sl' becomes : 0x815c + (0x83e4+8) = 0x10548
>>Which is the global offset table.
>>
>>r1, becomes 0x1c
>>r3, becomes 0x20
>>
>>
>>Afterwards, [sl, r1] is loaded :
>>  sl+r1 = 0x10564, which contains a (valid) pointer to the string '%p\n"
>>
>>Than, [sl, r3] is loaded, sl+r3 = 0x10568, which contains a NULL pointer.
>>(Thus, &var == NULL !!)
> 
> 
> Does it contain a NULL pointer at run time?

root:/usr/src/cvs-others/tmp3# ./a.out
(nil)


> 
> You didn't show the dynamic relocations in this binary.  The content of
> the GOT in the binary can be NULL if there is an appropriate relocation
> against var to fill it in.
> 
>

-
nm -D a.out
00008450 R _IO_stdin_used
          w __gmon_start__
          U __libc_start_main
          U abort
          U printf
00008454 R var

-
objdump -R a.out

a.out:     file format elf32-littlearm

DYNAMIC RELOCATION RECORDS
OFFSET   TYPE              VALUE
00010554 R_ARM_JUMP_SLOT   abort
00010558 R_ARM_JUMP_SLOT   __libc_start_main
0001055c R_ARM_JUMP_SLOT   printf
-
objdump -r a.out

a.out:     file format elf32-littlearm

-
So, the 'var' symbol will not be relocated, nor will it have the correct value at run time...
I guess there are two solutions (from my original mail) :

> So, I have the impression that there are two possibilities :
> - the location of the symbol is known already, but we let the dynamic linker resolve it
>   at run time.
>   -> in this case there should be a symbol added (somehow) to indicate this to the dynamic linker

This symbol has not been added...

> - the location of the symbol is known already and we should fill it in here...
>   -> in this case, we should find out the address of the symbol (in stead of 0).

What would be the prefered solution for this case ? (and how can it be done ;) ? )

Greetings,
-- 
Jeroen Dobbelaere
Embedded Software Engineer

ACUNIA Embedded Solutions
http://www.acunia.com/aes