cortexm_common: use of r13 is deprecated

[miri64]

Since the merge of #3333 I get the following warning:

$ BOARD=iot-lab_M3 IOTLAB_NODES=2 make -C examples/gnrc_networking/ all
make: Entering directory `/home/martine/Repositories/RIOT-OS/RIOT/examples/gnrc_networking'
Building application "gnrc_networking" for "iot-lab_M3" with MCU "stm32f1".

"make" -C /home/martine/Repositories/RIOT-OS/RIOT/boards/iot-lab_M3
"make" -C /home/martine/Repositories/RIOT-OS/RIOT/core
"make" -C /home/martine/Repositories/RIOT-OS/RIOT/cpu/stm32f1
"make" -C /home/martine/Repositories/RIOT-OS/RIOT/cpu/cortexm_common
/tmp/ccwJhJJ3.s: Assembler messages:
/tmp/ccwJhJJ3.s:211: Warning: use of r13 is deprecated
"make" -C /home/martine/Repositories/RIOT-OS/RIOT/cpu/stm32f1/periph
[…]

[jnohlgard]

I will look into this.

[thomaseichinger]

The line causing this is vectors_cortexm.c:137.

cmp r0, sp doesn't seem to be suspicious on first sight.

[OlegHahm]

I think make scan-build was reporting this since it was introduced.

[thomaseichinger]

Oops, r13 is sp. Forgot about this. 😬

[daniel-k]

I found this after googling. But I couldn't find the ARM docs yet, that mention this.

[thomaseichinger]

Found this too, cmp sp, r0 would be allowed.

[jnohlgard]

yes, the solution is to mov r1, sp first, then cmp r0, r1

[thomaseichinger]

Some register juggling. 😄

[thomaseichinger]

As reference

Use of SP in ARM and Thumb instructions
You can use SP for Rn in ARM and Thumb instructions.
You can use SP for Rm in ARM instructions but this is deprecated in ARMv6T2 and above.
You can use SP for Rm in a 16-bit Thumb CMP Rn, Rm instruction but this is deprecated in ARMv6T2 and above. Other use of SP for Rm is not permitted in Thumb.

[miri64]

@PeterKietzmann please explain why you closed this issue.

[PeterKietzmann]

It was automatically closed after I merged #3666. Isn't it fixed for you?

[miri64]

Ah, sorry. Somehow I landed in #3356 and this wasn't merged yet.