bootloader_util.c does not compile with GCC without -Os option

[Jacob Portukalian]

If I try to build my project using GCC and I change the optimization flag to something other than -Os then I get the following error:

D:/Nordic/nRF51_SDK_8.1.0_b6ed55f/components/libraries/bootloader_dfu/bootloader_util.c: In function 'bootloader_util_reset': D:/Nordic/nRF51_SDK_8.1.0_b6ed55f/components/libraries/bootloader_dfu/bootloader_util.c:106:1: error: r7 cannot be used in asm here } ^ Is there any way to fix this?

[Clem Taylor]

It may just be a matter of using '+l' instead of '+r' or 'r' for the start_addr flags. I'm not sure, my code won't fit without '-Os -flto' and aggressive dead stripping.

[RK]

Turn -fomit-frame-pointer on for that one file.

[Jacob Portukalian]

That worked. Thanks! The hard part was getting the makefile to use a different set of options for one file.

[RK]

yes I skipped over the how as makefiles are not my speciality. The reason by the way is that the ARM ABI uses r7 as the frame pointer in Thumb mode (r11 in ARM mode), which is why you almost always see

push {r7, lr}
sub sp, sp, <some number>
add r7, sp, #0

at the start of every function in debug mode. The debugger then knows where all the local copies of the variables are kept so it can show them. So gcc stops you using r7 in debug mode unless you tell it not to use the frame pointer. if you turn it off globally that works too, but your code becomes very hard to debug.