arm-elf-ld: problems with long calls in thumb mode

arm-elf-ld: problems with long calls in thumb mode

[Lars Olsson]

Hi,

I'm working on a platform with an arm7tdmi chip with a large (but slow)
flashrom and a small, fast sram. Code is in thumb mode. The flashrom is used to 
store collected data as well as providing non-volatile storage for the program 
code. On bootstrap, all code is copied from flash to ram because speed is of 
essence. This works as intended.

However, I'm getting to the point where I'm running out of ram and I would like 
to skip copying non-critical functions to ram in order to save some space and 
here I experience problems with the linker:

thumb/send.o(.text+0x10): In function `InitRS232':
send.c:39: relocation truncated to fit: R_ARM_THM_PC22 _call_via_r3
thumb/send.o(.text+0x20):send.c:40: relocation truncated to fit: R_ARM_THM_PC22 
_call_via_r3
thumb/send.o(.text+0x58): In function `SendData':
send.c:71: relocation truncated to fit: R_ARM_THM_PC22 _call_via_r4
thumb/send.o(.text+0x60):send.c:72: relocation truncated to fit: R_ARM_THM_PC22 
_call_via_r4
thumb/send.o(.text+0x6a):send.c:76: relocation truncated to fit: R_ARM_THM_PC22 
_call_via_r3
thumb/send.o(.text+0x7a):send.c:79: relocation truncated to fit: R_ARM_THM_PC22 
_call_via_r4
thumb/send.o(.text+0x8c):send.c:82: relocation truncated to fit: R_ARM_THM_PC22 
_call_via_r3
thumb/send.o(.text+0xa0):send.c:83: relocation truncated to fit: R_ARM_THM_PC22 
_call_via_r4
thumb/send.o(.text+0xa6):send.c:85: relocation truncated to fit: R_ARM_THM_PC22 
_call_via_r3
thumb/send.o(.text+0xda):send.c:103: relocation truncated to fit: 
R_ARM_THM_PC22 _call_via_r3
thumb/send.o(.text+0xea):send.c:106: additional relocation overflows omitted 
from the output

I have looked for information regarding this behaviour and I've seen
that other people have also run into similar situations, but I haven't
found a solution. The problem seems to be that the 'bl' instruction can't 
bridge the gap between flash and ram so the linker tries to use the 
_call_via_rX routines as intermediates. However, these routines are in libgcc 
which are linked only to the ram address which means they too are unreachable 
from flash! Is there anyway to get the linker to smarten up and place these 
routines in flash as well as in ram so that functions can be called from either 
place?


Thanks,
/Lars

Re: arm-elf-ld: problems with long calls in thumb mode

[Richard Earnshaw]

On Thu, 2005-02-24 at 10:08, Lars Olsson wrote:
> Hi,
> 
> I'm working on a platform with an arm7tdmi chip with a large (but slow)
> flashrom and a small, fast sram. Code is in thumb mode. The flashrom is used to 
> store collected data as well as providing non-volatile storage for the program 
> code. On bootstrap, all code is copied from flash to ram because speed is of 
> essence. This works as intended.
> 
> However, I'm getting to the point where I'm running out of ram and I would like 
> to skip copying non-critical functions to ram in order to save some space and 
> here I experience problems with the linker:
> 
> thumb/send.o(.text+0x10): In function `InitRS232':
> send.c:39: relocation truncated to fit: R_ARM_THM_PC22 _call_via_r3
> thumb/send.o(.text+0x20):send.c:40: relocation truncated to fit: R_ARM_THM_PC22 
> _call_via_r3
> thumb/send.o(.text+0x58): In function `SendData':
> send.c:71: relocation truncated to fit: R_ARM_THM_PC22 _call_via_r4
> thumb/send.o(.text+0x60):send.c:72: relocation truncated to fit: R_ARM_THM_PC22 
> _call_via_r4
> thumb/send.o(.text+0x6a):send.c:76: relocation truncated to fit: R_ARM_THM_PC22 
> _call_via_r3
> thumb/send.o(.text+0x7a):send.c:79: relocation truncated to fit: R_ARM_THM_PC22 
> _call_via_r4
> thumb/send.o(.text+0x8c):send.c:82: relocation truncated to fit: R_ARM_THM_PC22 
> _call_via_r3
> thumb/send.o(.text+0xa0):send.c:83: relocation truncated to fit: R_ARM_THM_PC22 
> _call_via_r4
> thumb/send.o(.text+0xa6):send.c:85: relocation truncated to fit: R_ARM_THM_PC22 
> _call_via_r3
> thumb/send.o(.text+0xda):send.c:103: relocation truncated to fit: 
> R_ARM_THM_PC22 _call_via_r3
> thumb/send.o(.text+0xea):send.c:106: additional relocation overflows omitted 
> from the output
> 
> I have looked for information regarding this behaviour and I've seen
> that other people have also run into similar situations, but I haven't
> found a solution. The problem seems to be that the 'bl' instruction can't 
> bridge the gap between flash and ram so the linker tries to use the 
> _call_via_rX routines as intermediates. However, these routines are in libgcc 
> which are linked only to the ram address which means they too are unreachable 
> from flash! Is there anyway to get the linker to smarten up and place these 
> routines in flash as well as in ram so that functions can be called from either 
> place?
> 
> 
> Thanks,
> /Lars

This is gcc PR target/7525.  It's been fixed for gcc-4 for other
reasons, but it's not going to get back-ported onto any older compilers
since it doesn't fix a regression.  You can try using the trunk
compiler, or you could try and back-port the change yourself if you
wished, but it might require some adjustment to work with the older
code.

R.

Re: arm-elf-ld: problems with long calls in thumb mode

[Vincent Rubiolo]

Hello,

I encountered the problem before and Nick was kind enough to direct me 
to an experimental patch (which worked for me at the time). This 
involves patching and rebuilding gcc. YMMV as this is quite old but this 
may work.

Here is the corresponding binutils discussion (some time has passed 
obviously, Richard was still working for ARM :)
http://sources.redhat.com/ml/binutils/2003-06/msg00412.html

HTH,

Vincent

Richard Earnshaw wrote:
[...]
> This is gcc PR target/7525.  It's been fixed for gcc-4 for other
> reasons, but it's not going to get back-ported onto any older compilers
> since it doesn't fix a regression.  You can try using the trunk
> compiler, or you could try and back-port the change yourself if you
> wished, but it might require some adjustment to work with the older
> code.
> 
> R.

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